Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 18831-2010 Safety of machinery—Interlocking devices associated with guards—Principles for design and selection. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 18831-2010:
——26 terms such as "defeat", "holding force" and "actuator" are added, and 3 terms such as "positive mode actuation", "positive opening operation of contact elements" and "stop time" are deleted (see Clause 3 hereof, Clause 3 of Edition 2010);
——The sub-clause 5.7 is adjusted to Clause 7 (see Clause 7 hereof; 5.7 of Edition 2010);
——The control requirements are added (see Clause 8 hereof);
——The content in Clause 6 is adjusted into 8.7 (see 8.7 hereof; Clause 6 of Edition 2010);
——The requirements for information for use are added (see Clause 9 hereof);
——According to the newly defined interlocking device types, the contents of Annex A to Annex M are integrated and rearranged into Annex A to Annex E (see Annex A to Annex E hereof, Annex A to Annex M of Edition 2010);
——The informative annex F "Example of guard locking devices" is added (see Annex F hereof);
——The informative annex G "Application examples of interlocking devices used within a safety function" is added (see Annex G hereof);
——The informative annex H "Motivation to defeat interlocking device" is added (see Annex H hereof);
——The informative annex I "Examples for maximum static action forces" is added (see Annex I hereof).
This standard is, by means of translation, identical to ISO 14119: 2013 Safety of machinery—Interlocking devices associated with guards—Principles for design and selection (English edition).
The Chinese documents consistent and corresponding with the normative international documents in this standard are as follows:
——GB 5226.1-2008 Electrical safety of machinery—Electrical equipment of machines—Part 1: General requirements (IEC 60204-1: 2005, IDT)
——GB/T 14048.13-2006 Low-voltage switchgear and controlgear—Part 5-3: Control circuit devices and switching elements - Requirements for proximity devices with defined behaviour under fault conditions(PDF) (IEC 60947-5-3: 1999, IDT)
——GB 28526-2012 Electrical safety of machinery—Functional safety of safety-related electrical, electronic and programmable electronic control systems (IEC 62061: 2005, IDT)
This standard was proposed by and is under the jurisdiction of the National Technical Committee on Machinery Safety of Standardization Administration of China (SAC/TC 208).
The previous editions of this standard are as follows:
——GB/T 18831-2002, GB/T 18831-2010.
Introduction
The structure of safety standards in the field of machinery is as follows:
——Type-A standards (basic safety standards) giving basic concepts, principles for design, and general aspects that can be applied to all machinery;
——Type-B standards (generic safety standards) dealing with one safety aspect or one type of safeguard that can be used across a wide range of machinery;
Type-B1 standards on particular safety aspects (e.g. safety distances, surface temperature, noise);
Type-B2 standards on safeguards (e.g. two-hand controls, interlocking devices, pressure sensitive devices, guards);
——Type-C standards (machine safety standards) dealing with detailed safety requirements for a particular machine or group of machines.
This document is a Type-B2 standard as stated in IGB/T 15706.
The requirements of this document may be supplemented or modified by a Type-C standard.
For machines which are covered by the scope of a Type-C standard and which have been designed and built according to the requirements of that standard, the requirements of that Type-C standard take precedence.
This standard has been prepared to give guidance to machinery designers and writers of product safety standards on how to design and select interlocking devices associated with guards.
Relevant clauses of this standard, used alone or in conjunction with provisions from other standards, may be used as a basis for verification procedures for the suitability of a device for interlocking duties.
The informative Annexes A to F describe the technology and the typical characteristics of the defined 4 types of interlocking devices. Other solutions may be adopted, provided that they comply with the principles of this standard. The informative Annexes G to I give information on particular aspects like interlocking devices used within safety functions, risk assessment considering the motivation to defeat and static action forces. ISO/TR 24119 is under preparation and will give information on the masking of faults in series connection of interlocking devices.
Safety of machinery—Interlocking devices associated with guards—
Principles for design and selection
1 Scope
This standard specifies principles for the design and selection—independent of the nature of the energy source—of interlocking devices associated with guards.
This standard covers the parts of guards which actuate interlocking devices.
Note: ISO 14120 specifies general requirements for the design and construction of guards provided primarily to protect persons from mechanical hazards. The processing of the signal from the interlocking device to stop and immobilize the machine is dealt with in GB/T 16855.1 or IEC 62061.
This standard does not necessarily provide all the specific requirements for trapped key systems.
This standard provides measures to minimize defeat of interlocking devices in a reasonably foreseeable manner:
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 15706-2012 Safety of machinery—General principles for design—Risk assessment and risk reduction (ISO 12100: 2010, IDT)
GB/T 16855.1-2008 Safety of machinery—Safety-related parts of control systems—Part 1: General principles for design (ISO 13849-1: 2006, IDT)
GB/T 16855.2-2015 Safety of machinery—Safety-related parts of control systems—Part 2: Validation (ISO 13849-2: 2012, IDT)
IEC 60947-5-3 Low-voltage switchgear and controlgear—Part 5-3: Control circuit devices and switching elements—Requirements for proximity devices with defined behaviour under fault conditions (PDF)
IEC 60204-1: 2009 Safety of machinery—Electrical equipment of machines—Part 1: General requirements
IEC 62061: 2012 Safety of machinery—Functional safety of safety-related electrical, electronic and programmable electronic control systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 15706 and GB/T 16855.1 and the following apply.
3.1
interlocking device
interlock
mechanical, electrical or other type of device, the purpose of which is to prevent the operation of hazardous machine functions under specified conditions (generally as long as a guard is not closed)
Note: See Figure 1 and Table 1.
[GB/T 15706-2012, Definition 3.28.1]
Key:
1––—guard; 4——position switch;
2——interlocking device; 5——actuating system;
3——actuator; 6——output system.
a——direction of opening;
Figure 1 Example of an interlocking device
3.2
interlocking guard
guard associated with an interlocking device so that, together with the control system of the machine, the following functions are performed:
——the hazardous machine functions “covered” by the guard cannot operate until the guard is closed;
——if the guard is opened while hazardous machine functions are operating, a stop command is given;
——when the guard is closed, the hazardous machine functions “covered” by the guard may operate (the closure of the guard does not by itself start the hazardous machine functions). An interlocking guard can contain/be equipped of one or more interlocking devices.
Note: An interlocking guard can contain/be equipped of one or more interlocking devices. These interlocking devices can also be of different types.
[GB/T 15706-2012, Definition 3.27.4]
3.3
interlocking guard with a start function
control guard
special form of interlocking guard which, once it has reached its closed position, gives a command to initiate the hazardous machine function(s) without the use of a separate start control
Note: GB/T 15706-2012, 6.3.3.2.5 gives detailed provisions regarding the condition of use.
[GB/T 15706-2012, Definition 3.27.6]
3.4
guard locking device
device intended to lock a guard in the closed position and linked to the control system
3.5
interlocking guard with guard locking
guard associated with an interlocking device and a guard locking device so that, together with the control system of the machine, the following functions are performed:
——the hazardous machine functions "covered" by the guard cannot operate until the guard is cIosed and Iocked;
——the guard remains closed and Iocked until the risk due to the hazardous machine functions "covered” by the guard has disappeared;
——when the guard is closed and locked, the hazardous machine functions "covered" by the guard can operate. The closure and locking of the guard do not by themselves start the hazardous machine functions
[GB/T 15706-2012, Definition 3.27.5]
3.6
safety-related part of a control system
SRP/CS
part of a control system that responds to safety-related input signals and generates safety-related output signals
Note 1: The combined safety-related parts of a control system start at the point where the safety-related input signals are initiated (including e.g. the actuating cam and the roller of the position switch) and end at the output of the power control elements (including, for example, the main contacts of a contactor).
Note 2: If monitoring systems are used for diagnostics, they are also considered as SRP/CS.
Note 3: It is revised from GB/T 16855.1-2008, Definition 3.1.1.
3.7
defeat
action that makes interlocking devices inoperative or bypasses them with the result that a machine is used in a manner not intended by the designer or without the necessary safety measures
3.8
defeat in a reasonably foreseeable manner
defeat of an interlocking device either manually or by using readily available objects
Note 1: This definition includes the removal of switches or actuators using tools that are needed for the intended use of the machine or that are readily available (screw drivers, wrenches, hexagon keys, pliers).
Note 2: Readily available objects for substitute actuation include:
——screws, needles and sheet-metal pieces;
——objects in daily use such as keys, coins, adhesive tape, string and wire;
——spare keys for the trapped-key interlocking devices;
——spare actuators.
3.9
automatic monitoring
diagnostic function which initiates a fault reaction function if the ability of a component or an element to perform its function is diminished, or if the process conditions are changed in such a way that hazards are generated
3.10
direct mechanical action
positive mechanical action
movement of a mechanical component which arises inevitably from the movement of another mechanical component either by direct contact or via rigid elements
3.11
direct opening action
positive opening operation
achievement of contact separation as a direct result of a specified movement of the switch actuator through non-resilient members (for example not dependent upon springs)
Note: It is revised from IEC 60947-5-1: 2003, Definition K.2.2.
3.12
actuator
separate part of an interlocking device which transmits the state of the guard (closed or not closed) to the actuating system
Example: Guard-mounted cam, key, shaped tongue, reflector, magnet, RFID tag.
Note 1: See also Annexes A to E.
Note 2: Examples of actuators are shown in Figure 2.
3.13
coded actuator
actuator which is specially designed (e.g. by shape) to actuate a certain position switch
3.13.1
low level coded actuator
coded actuator for which 1 to 9 variations in code are available
3.13.2
medium level coded actuator
coded actuator for which 10 to 1,000 variations in code are available
3.13.3
high level coded actuator
coded actuator for which more than 1,000 variations are available
3.14
actuating system
part of the interlocking device which transmits the position of the actuator and changes the state of the output system
Example: Roller plunger, cam mechanism, optical, inductive or capacitive sensor.
Note: Examples of actuating systems are shown in Figure 2.
3.15
output system
part of the interlocking device that indicates the state of the guard to the control system
Example: Contact element (electromechanical), semiconductor output, valve.
3.16
type 1 interlocking device
interlocking device with mechanically actuated position switch with uncoded actuator
Example: Hinged interlocking devices.
Note: See Annex A for detailed examples.
3.17
type 2 interlocking device
interlocking device with mechanically actuated position switch with coded actuator
Example: Tongue-actuated position switches.
Note: See Annex B for detailed examples.
3.18
type 3 interlocking device
interlocking device with non-contact actuated position switch with uncoded actuator
Example: Proximity switches.
Note: See Annex C for detailed examples.
3.19
type 4 interlocking device
interlocking device with non-contact actuated position switch with coded actuator
Example: RFID tag actuated position switches.
Note: See Annex D for detailed examples.
3.20
stop command
signal generated by the interlocking device that causes the hazardous machine function to disappear
3.21
overall system stopping performance
time interval between the stop command given by opening the guard and the termination of the hazardous machine function
Note: It is revised from GB/T 19876-2012, Definition 3.1.2.
3.22
access time
time taken by a person to reach the hazard zone after initiation of the stop command by the interlocking device, as calculated on the basis of an approach speed of the body or part of the body
Note: For the selection of the approach speed and the calculation of the access time, see GB/T 19876.
3.23
holding force
force that a guard locking device can withstand without being damaged so that its further use will not be impaired and the guard will not leave the closed position
3.24
prevention of inadvertent locking position
feature of a guard locking device which ensures that the locking means (e.g. a locking bolt) cannot take the locked position when the guard is not closed
3.25
emergency release of guard locking
possibility to release manually without aids the guard locking from outside the safeguarded area in case of an emergency
Note: The guard locking with emergency release can be necessary for releasing trapped persons or fire-fighting, for example.
3.26
auxiliary release of guard locking
possibility to release manually by means of a tool or a key the guard locking from outside the safeguarded area in case of its failure
Note: The guard locking with auxiliary release is not suitable for emergency or escape release of guard locking.
3.27
escape release of guard locking
possibility to release manually without aids the guard locking from inside the safeguarded area to leave the area
3.28
guard locking for protection of a person
application of a guard locking device to protect a person against a hazard
3.29
guard locking for protection of the process
application of a guard locking device to protect the working process from being interrupted
3.30
tool
implement such as a key or wrench designed to operate a fastener
Note: An improvised implement such as a coin or a nail file cannot be considered as a tool.
[ISO 14120: 2002, Definition 3.9]
3.31
power interlocking
interlocking which directly interrupts the energy supply to the machine actuators or disconnects moving parts from the machine actuators
Note: Resumption of the energy supply is only possible with the guard in the closed and locked position. “Directly” means that, unlike control interlocking, the control system does not play any intermediate role in the interlocking function.
3.32
safety function
function of a machine whose failure can result in an immediate increase of the risk(s)
[GB/T 15706-2012, Definition 3.30]
4 Operating principles and typical forms of interlocking devices associated with guards
4.1 General
Interlocking techniques involve a broad spectrum of technological aspects. Interlocking devices may be classified using a great variety of criteria, e.g. the nature of the link between guard and output system, or the technological type (electromechanical, pneumatic, electronic, etc.) of the output system.
Interlocking devices have a guard position monitoring function that senses whether the guard is closed or not and produce a stop command when the guard is not in the closed position. An interlocking device may also be used in the control of other functions e.g. application of a brake to stop hazardous machine functions before access is possible. Some interlocking devices also have a guard locking function to keep the guard locked while hazardous machine function is present. A guard locking device status monitoring function monitors whether the guard locking device is locked or unlocked and produces an appropriate output signal [see 4.3.1a) and b)].
Note 1: The guard locking device (see 3.4) may be an integral part of an interlocking device, or a separate unit.
Note 2: See also GB/T 15706-2012, 6.3.3.1 for additional information on guards.
Note 3: The four types of interlocking device are not shown in Table 1 and presented in a hierarchical order. The correct application of each type of interlocking device will be dependent on the risk assessment that shall be made for the specific machine.
Table 1 shows the actuation principles and actuators for the defined interlocking device types.
Table 1 Overview of interlocking devices
Actuation principle examples Actuator examples Type Examples: see Annex a
Mechanical Physical contact/force Uncoded Rotating cam Type 1 A.1
Linear cam A.2, A.4
Hinge A.3
Coded Tongue (-shaped actuator) Type 2 B.1
Trapped-key B.2
Non-contact Inductive Uncoded Suitable ferric metal Type 3 C
Magnetic Magnet, solenoid
Capacitive Any suitable object
Ultrasonic Any suitable object
Optic Any suitable object
Magnetic Coded Coded magnet Type 4 D.1
RFID Coded RFID tag D.2
Optic Optically coded tag —
a Examples of other interlocking guards are given in Annex E.
Key:
1——movable guard; 4——position switch;
2——interlocking device; 5——actuating system;
3——actuator; 6——output system.
a Cam; c E.g. RFID, reflector, suitable surface;
b Tongue; d Movement direction.
Note: In some exceptional cases, the position switch can be installed on the movable guard and the actuator on the stationary part of the machine. In these cases, “1” is the stationary part of the machine.
Figure 2 Principle of types 1, 2, 3 and 4 interlocking devices
4.2 Principles of guard interlocking without guard locking
When guard interlocking function without guard locking is used, the guard can be opened at any time regardless of the function of the machine.
If the guard is not closed, the interlocking device shall generate a stop command.
Note 1: For interlocking with the machine control system, see Clause 8.
Note 2: Examples of interlocking devices without guard locking are shown in Annexes A, B, C and D.
Note 3: A functional diagram of interlocking devices without guard locking is shown in Figure 3.
Figure 3 Functional diagram of interlocking devices without guard locking
4.3 Principles of guard interlocking with guard locking
4.3.1 General
When interlocking with guard locking is applied, opening of the guard shall be prevented by a guard locking device (see 3.4) unless all hazardous machine functions covered by this guard have disappeared.
There are two alternatives for the design of the guard locking function (see Figure 4).
a) Unlocking of the guard can be initiated at any time by the operator. When unlocking is started, the guard locking device generates a stop command. This is called unconditional unlocking. The time necessary for the guard to be unlocked shall be greater than the time necessary for the hazardous machine function to disappear.
b) Unlocking of the guard is possible only when the hazardous machine functions have disappeared. This is called conditional unlocking.
Note: In conditional locking, the change from state 2 to state 3 or from state 3 to state 2 can happen without time delay.
Figure 4 Functional diagrams of interlocking devices with guard locking
Examples of guard locking devices are given in Annex F.
4.3.2 Interlocking device with mechanically operated guard locking
The mechanical part (e.g. bolt) which locks the interlocking guard may be:
——manually applied and manually released (see Figure F.5);
——spring (or similar) applied and power-ON released [see Figure 5a)];
——power-ON applied and spring (or similar) released [see Figure 5b)];
——power-ON applied and power-ON released [see Figure 5c)].
Mechanically operated guard locking shall use the principle of direct mechanical blocking due to form. Friction and force alone shall not be relied upon.
a) Spring applied Locking
Power-ON released Unlocking
b) Power-ON applied Locking
Spring released Unlocking
c) Power-ON applied Locking
Power-ON released Unlocking
d) Power-ON applied Locking
Power-ON released Unlocking
Figure 5 Operating modes of guard locking device in power-actuated guard locking devices
4.3.3 Interlocking device with electromagnetically operated guard locking
The guard is kept closed (locked) without any mechanical locking means by an electromagnetic force (see F.4).
The electromagnetic guard locking operates on the principle of power-ON applied and power-OFF released [see Figure 5d)].
5 Requirements for the design and the installation of interlocking devices with and without guard locking
5.1 General
Interlocking devices shall be installed in a suitable robust manner and in accordance with any instructions provided by the manufacturer (see Clause 9).
5.2 Arrangement and fastening of position switches
Position switches shall be arranged so that they are sufficiently protected against a change of their position. In order to achieve this, the following requirements shall be met:
a) fasteners of the position switches shall be reliable and loosening them shall require a tool;
b) type 1 position switches shall have provisions for permanently fixing the location after adjustment (e.g. by means of pins or dowels);
c) necessary means of access to position switches for maintenance and checking for correct operation shall be ensured. Prevention of defeat in a reasonably foreseeable manner shall also be considered when designing the access means;
d) self-loosening shall be prevented;
e) defeat of the position switch in a reasonably foreseeable manner shall be prevented (see Clause 7);
f) the position switch shall be located and, if necessary, protected so that damage from foreseeable external causes is avoided;
g) the movement produced by mechanical actuation or the gap of the proximity device actuating system shall remain within the specified operating range of the position switch or actuating system specified by the switch manufacturer to ensure correct operation and/or prevent overtravel;
h) a position switch shall not be used as a mechanical stop, unless this is the intended use of the position switch as declared by the manufacturer;
i) misalignment of the guard that creates a gap before the position switch changes its state shall not be sufficient as to impair the protective effect of the guard (for access to hazard zones, see ISO 13855 and ISO 13857);
j) the support and fastening for the position switches shall be sufficiently rigid to maintain correct operation of the position switch.
5.3 Arrangement and fastening of actuators
5.3.1 General
Actuators (see Figure 2) shall be so fastened to minimize the possibility that they come loose or change their intended position relative to the actuating system during the intended lifetime.
Note: A regular check can be necessary (see 9.3.2).
The following requirements shall be met:
a) fasteners of the actuators shall be reliable and loosening them shall require a tool;
b) self-loosening shall be prevented;
c) the position switch shall be located and, if necessary, protected so that damage from foreseeable external causes is avoided;
d) an actuator shall not be used as a mechanical stop, unless this is the intended use of the actuator as declared by the manufacturer;
e) the support and fastening for the actuators shall be sufficiently rigid to maintain correct operation of the actuator.
5.3.2 Cams
Rotary and linear cams for type 1 interlocking devices shall meet the following requirements:
a) they are fixed by fasteners requiring a tool for loosening them;
b) final fixing is achieved by form (e.g. spline or pin) or other methods that provide equivalent integrity of fixing;
c) they do not damage the position switch or impair its durability.
5.4 Actuation modes of interlocking devices
When a single type 1 or type 2 interlocking device is used to generate a stop command, it shall be actuated by direct mechanical action between guard, actuator and output system and the contact element shall have direct opening action (see 3.10, 3.11 and Table 2).
Non-direct mechanical action for a type 1 interlocking device shall be used only in conjunction with a type 1 or type 2 interlocking device with direct mechanical action between guard, actuator and output system. Combining one interlocking device with direct mechanical action with a second interlocking device with non-direct mechanical action avoids common cause failures (see 8.3).
Table 2 Direct and non-direct mechanical action of type 1 interlocking devices
Mechanical action Guard closed Guard not closed Working mode Example of behaviour in case of failure (see 8.3.2)
Direct Plunger held depressed by cam as long as guard is not closed.
When guard closed, output system changes, its state as result of action of return spring. Output system remains in safe state when guard is not closed even if spring breaks.
Non-direct The plunger is held depressed by a cam as long as the guard is closed.
When guard not closed, output system changes state as result of action of return spring. If spring breaks, output system can go to unsafe state even if guard not closed.
Interlocking devices shall be actuated appropriate to the actuation principle of the applied position switch.
If a type 3 or type 4 interlocking device is the only interlocking device, it shall meet the requirements of IEC 60947-5-3.
5.5 Interface to control systems
The output system of interlocking devices shall be suitable for inclusion in a control system designed in accordance with GB/T 16855.1 or IEC 62061.
5.6 Mechanical stop
If an interlocking device is declared by the manufacturer of the device to be suitable for use as a mechanical stop the maximum impact energy withstand value shall be given [see also 9.2.2 r)].
5.7 Additional requirements on guard locking devices
5.7.1 General
If the application of the guard locking function creates hazards, additional measures shall be considered (see 5.7.5 and GB/T 15706-2012, 6.3.5.3).
The locking element (e.g. bolt) intended to lock the guard shall be “spring applied – power-ON released” [see Figure 5a)] or “power-ON applied – power-ON released” [see Figure 5c)] unless the outcome of the risk assessment shows that this is not appropriate. If other systems [e.g. Figure 5b)] are used in a specific application, they shall provide an equivalent level of safety.
Note: When the loss of power results in the release of the locking element, the stopping time of the machine is often lengthened considerably and it can be possible to access to the hazard before the movements have been stopped (or other hazards disappeared).
The requirements of 5.7 apply when guard locking function is used for the protection of persons. While the requirements of 5.7 do not apply when guard locking function is used solely for the protection of a process. Nevertheless, if guard locking function and guard interlocking function are part of the same device the safety level of the guard interlocking function shall not be negatively affected by a non safety related guard locking function (i. e. guard locking function used solely for the protection of the process).
The requirements of 5.7 apply to both guard locking devices composed of separate components as well as to guard locking devices which form an integral part of an interlocking device with guard locking. They apply to all technologies.
The guard locking device shall allow the locked position to be monitored by providing an output system compatible with a control system designed in accordance with GB/T 16855.1 or IEC 62061.
The guard locking device shall only allow hazardous functions of the machine when the guard is closed and locked.
5.7.2 Mechanical guard locking device
5.7.2.1 General
Mechanically operating guard locking shall result from the engagement of two rigid parts [form closure, see Figure 5a) to c)].
If it is foreseeable that access is necessary in case of emergency, for “spring applied – power-ON released” or “power-ON applied – power-ON released” systems [see Figure 5a) and c)], a guard locking device with emergency release (see 5.7.5.3) shall be provided.
Figure 6 shows the functionality of such a device.
5.7.2.2 Locking monitoring
The locked position of the locking element shall be monitored in accordance with the requirements of 5.5.
The hazardous function of the machine shall only be possible when the monitoring detects the closed position of the guard and the locked position of the locking element (see Annex F).
For an effective monitoring of the guard locking device, one of the following methods shall be ensured:
——the locking element can only go in the locked position if the movable guard is in the closed position (see Figure 6), in that case the closed position and the locking of the guard can be checked by the monitoring of the locking element;
——in the other case, the monitoring of the locking element and additionally the monitoring of the guard position shall be used for interlocking.
Key:
a)——guard closed and locked; 1——actuator (tongue);
b)——guard closed and not locked; 2——locking element (bolt);
c)——guard not closed and not locked; 3——actuating system (internal rotating cam).
Note: In this kind of position switch, the actuator has two functions: to operate the contacts (not shown in the figure) and together with the internal rotating cam and the bolt to provide the guard locking function. The bolt may be operated by external means e.g. a solenoid or pneumatic cylinder.
Figure 6 Example of type 2 interlocking device with guard locking
5.7.3 Electromagnetic guard locking device
5.7.3.1 General
The force required for the locking of the guard is applied by the generation of an electromagnetic field [see Figure 5d)].
5.7.3.2 Locking monitoring
The holding force shall be monitored to determine if the specified holding force has been achieved and maintained (see 6.2.2 and Annex I).
The hazardous function of the machine shall only be possible when the monitoring detects the closed position of the guard and the achievement of the specified holding force.
5.7.3.3 Basic measures for minimizing defeat possibilities
If an electromagnetic guard locking device is opened by force, it shall be ensured that the process cannot be immediately continued.
Note: In contrast to a mechanical guard locking, an electromagnetic guard locking shows no damage after an opening by force.
The objective of the measure is that an opening by force results in a time expenditure which is similar to that of repair works (time delay) and comparable with the repair of a damage of an electromechanical guard locking.
Foreword i
Introduction iii
1 Scope
2 Normative references
3 Terms and definitions
4 Operating principles and typical forms of interlocking devices associated with guards
4.1 General
4.2 Principles of guard interlocking without guard locking
4.3 Principles of guard interlocking with guard locking
5 Requirements for the design and the installation of interlocking devices with and without guard locking
5.1 General
5.2 Arrangement and fastening of position switches
5.3 Arrangement and fastening of actuators
5.5 Interface to control systems
5.6 Mechanical stop
5.7 Additional requirements on guard locking devices
6 Selection of an interlocking device
6.1 General
6.2 Selection of a guard locking device
6.3 Environmental conditions considerations
7 Design to minimize defeat possibilities of interlocking devices
7.1 General
7.2 Additional measures to minimize defeat possibilities of interlocking devices
8 Control requirements
8.1 General
8.2 Assessment of faults
8.3 Prevention of common cause failures
8.4 Release of guard locking device
8.5 Fault exclusion
8.6 Logical series connection of interlocking devices
8.7 Electrical and environmental conditions
9 Information for use
9.1 General
9.2 Information for use given by the manufacturer of interlocking devices
9.3 Information for use given by the manufacturer of the machine
Annex A (Informative) Type 1 interlocking device — Examples
Annex B (Informative) Type 2 interlocking device — Examples
Annex C (Informative) Type 3 interlocking device — Examples
Annex D (Informative) Type 4 interlocking device — Examples
Annex E (Informative) Examples of other interlocking devices
Annex F (Informative) Example of guard locking devices
Annex G (Informative) Application examples of interlocking devices used within a safety function
Annex H (Informative) Motivation to defeat interlocking device
Annex I (Informative) Examples for maximum static action forces
Bibliography
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 18831-2010 Safety of machinery—Interlocking devices associated with guards—Principles for design and selection. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 18831-2010:
——26 terms such as "defeat", "holding force" and "actuator" are added, and 3 terms such as "positive mode actuation", "positive opening operation of contact elements" and "stop time" are deleted (see Clause 3 hereof, Clause 3 of Edition 2010);
——The sub-clause 5.7 is adjusted to Clause 7 (see Clause 7 hereof; 5.7 of Edition 2010);
——The control requirements are added (see Clause 8 hereof);
——The content in Clause 6 is adjusted into 8.7 (see 8.7 hereof; Clause 6 of Edition 2010);
——The requirements for information for use are added (see Clause 9 hereof);
——According to the newly defined interlocking device types, the contents of Annex A to Annex M are integrated and rearranged into Annex A to Annex E (see Annex A to Annex E hereof, Annex A to Annex M of Edition 2010);
——The informative annex F "Example of guard locking devices" is added (see Annex F hereof);
——The informative annex G "Application examples of interlocking devices used within a safety function" is added (see Annex G hereof);
——The informative annex H "Motivation to defeat interlocking device" is added (see Annex H hereof);
——The informative annex I "Examples for maximum static action forces" is added (see Annex I hereof).
This standard is, by means of translation, identical to ISO 14119: 2013 Safety of machinery—Interlocking devices associated with guards—Principles for design and selection (English edition).
The Chinese documents consistent and corresponding with the normative international documents in this standard are as follows:
——GB 5226.1-2008 Electrical safety of machinery—Electrical equipment of machines—Part 1: General requirements (IEC 60204-1: 2005, IDT)
——GB/T 14048.13-2006 Low-voltage switchgear and controlgear—Part 5-3: Control circuit devices and switching elements - Requirements for proximity devices with defined behaviour under fault conditions(PDF) (IEC 60947-5-3: 1999, IDT)
——GB 28526-2012 Electrical safety of machinery—Functional safety of safety-related electrical, electronic and programmable electronic control systems (IEC 62061: 2005, IDT)
This standard was proposed by and is under the jurisdiction of the National Technical Committee on Machinery Safety of Standardization Administration of China (SAC/TC 208).
The previous editions of this standard are as follows:
——GB/T 18831-2002, GB/T 18831-2010.
Introduction
The structure of safety standards in the field of machinery is as follows:
——Type-A standards (basic safety standards) giving basic concepts, principles for design, and general aspects that can be applied to all machinery;
——Type-B standards (generic safety standards) dealing with one safety aspect or one type of safeguard that can be used across a wide range of machinery;
Type-B1 standards on particular safety aspects (e.g. safety distances, surface temperature, noise);
Type-B2 standards on safeguards (e.g. two-hand controls, interlocking devices, pressure sensitive devices, guards);
——Type-C standards (machine safety standards) dealing with detailed safety requirements for a particular machine or group of machines.
This document is a Type-B2 standard as stated in IGB/T 15706.
The requirements of this document may be supplemented or modified by a Type-C standard.
For machines which are covered by the scope of a Type-C standard and which have been designed and built according to the requirements of that standard, the requirements of that Type-C standard take precedence.
This standard has been prepared to give guidance to machinery designers and writers of product safety standards on how to design and select interlocking devices associated with guards.
Relevant clauses of this standard, used alone or in conjunction with provisions from other standards, may be used as a basis for verification procedures for the suitability of a device for interlocking duties.
The informative Annexes A to F describe the technology and the typical characteristics of the defined 4 types of interlocking devices. Other solutions may be adopted, provided that they comply with the principles of this standard. The informative Annexes G to I give information on particular aspects like interlocking devices used within safety functions, risk assessment considering the motivation to defeat and static action forces. ISO/TR 24119 is under preparation and will give information on the masking of faults in series connection of interlocking devices.
Safety of machinery—Interlocking devices associated with guards—
Principles for design and selection
1 Scope
This standard specifies principles for the design and selection—independent of the nature of the energy source—of interlocking devices associated with guards.
This standard covers the parts of guards which actuate interlocking devices.
Note: ISO 14120 specifies general requirements for the design and construction of guards provided primarily to protect persons from mechanical hazards. The processing of the signal from the interlocking device to stop and immobilize the machine is dealt with in GB/T 16855.1 or IEC 62061.
This standard does not necessarily provide all the specific requirements for trapped key systems.
This standard provides measures to minimize defeat of interlocking devices in a reasonably foreseeable manner:
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 15706-2012 Safety of machinery—General principles for design—Risk assessment and risk reduction (ISO 12100: 2010, IDT)
GB/T 16855.1-2008 Safety of machinery—Safety-related parts of control systems—Part 1: General principles for design (ISO 13849-1: 2006, IDT)
GB/T 16855.2-2015 Safety of machinery—Safety-related parts of control systems—Part 2: Validation (ISO 13849-2: 2012, IDT)
IEC 60947-5-3 Low-voltage switchgear and controlgear—Part 5-3: Control circuit devices and switching elements—Requirements for proximity devices with defined behaviour under fault conditions (PDF)
IEC 60204-1: 2009 Safety of machinery—Electrical equipment of machines—Part 1: General requirements
IEC 62061: 2012 Safety of machinery—Functional safety of safety-related electrical, electronic and programmable electronic control systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 15706 and GB/T 16855.1 and the following apply.
3.1
interlocking device
interlock
mechanical, electrical or other type of device, the purpose of which is to prevent the operation of hazardous machine functions under specified conditions (generally as long as a guard is not closed)
Note: See Figure 1 and Table 1.
[GB/T 15706-2012, Definition 3.28.1]
Key:
1––—guard; 4——position switch;
2——interlocking device; 5——actuating system;
3——actuator; 6——output system.
a——direction of opening;
Figure 1 Example of an interlocking device
3.2
interlocking guard
guard associated with an interlocking device so that, together with the control system of the machine, the following functions are performed:
——the hazardous machine functions “covered” by the guard cannot operate until the guard is closed;
——if the guard is opened while hazardous machine functions are operating, a stop command is given;
——when the guard is closed, the hazardous machine functions “covered” by the guard may operate (the closure of the guard does not by itself start the hazardous machine functions). An interlocking guard can contain/be equipped of one or more interlocking devices.
Note: An interlocking guard can contain/be equipped of one or more interlocking devices. These interlocking devices can also be of different types.
[GB/T 15706-2012, Definition 3.27.4]
3.3
interlocking guard with a start function
control guard
special form of interlocking guard which, once it has reached its closed position, gives a command to initiate the hazardous machine function(s) without the use of a separate start control
Note: GB/T 15706-2012, 6.3.3.2.5 gives detailed provisions regarding the condition of use.
[GB/T 15706-2012, Definition 3.27.6]
3.4
guard locking device
device intended to lock a guard in the closed position and linked to the control system
3.5
interlocking guard with guard locking
guard associated with an interlocking device and a guard locking device so that, together with the control system of the machine, the following functions are performed:
——the hazardous machine functions "covered" by the guard cannot operate until the guard is cIosed and Iocked;
——the guard remains closed and Iocked until the risk due to the hazardous machine functions "covered” by the guard has disappeared;
——when the guard is closed and locked, the hazardous machine functions "covered" by the guard can operate. The closure and locking of the guard do not by themselves start the hazardous machine functions
[GB/T 15706-2012, Definition 3.27.5]
3.6
safety-related part of a control system
SRP/CS
part of a control system that responds to safety-related input signals and generates safety-related output signals
Note 1: The combined safety-related parts of a control system start at the point where the safety-related input signals are initiated (including e.g. the actuating cam and the roller of the position switch) and end at the output of the power control elements (including, for example, the main contacts of a contactor).
Note 2: If monitoring systems are used for diagnostics, they are also considered as SRP/CS.
Note 3: It is revised from GB/T 16855.1-2008, Definition 3.1.1.
3.7
defeat
action that makes interlocking devices inoperative or bypasses them with the result that a machine is used in a manner not intended by the designer or without the necessary safety measures
3.8
defeat in a reasonably foreseeable manner
defeat of an interlocking device either manually or by using readily available objects
Note 1: This definition includes the removal of switches or actuators using tools that are needed for the intended use of the machine or that are readily available (screw drivers, wrenches, hexagon keys, pliers).
Note 2: Readily available objects for substitute actuation include:
——screws, needles and sheet-metal pieces;
——objects in daily use such as keys, coins, adhesive tape, string and wire;
——spare keys for the trapped-key interlocking devices;
——spare actuators.
3.9
automatic monitoring
diagnostic function which initiates a fault reaction function if the ability of a component or an element to perform its function is diminished, or if the process conditions are changed in such a way that hazards are generated
3.10
direct mechanical action
positive mechanical action
movement of a mechanical component which arises inevitably from the movement of another mechanical component either by direct contact or via rigid elements
3.11
direct opening action
positive opening operation
achievement of contact separation as a direct result of a specified movement of the switch actuator through non-resilient members (for example not dependent upon springs)
Note: It is revised from IEC 60947-5-1: 2003, Definition K.2.2.
3.12
actuator
separate part of an interlocking device which transmits the state of the guard (closed or not closed) to the actuating system
Example: Guard-mounted cam, key, shaped tongue, reflector, magnet, RFID tag.
Note 1: See also Annexes A to E.
Note 2: Examples of actuators are shown in Figure 2.
3.13
coded actuator
actuator which is specially designed (e.g. by shape) to actuate a certain position switch
3.13.1
low level coded actuator
coded actuator for which 1 to 9 variations in code are available
3.13.2
medium level coded actuator
coded actuator for which 10 to 1,000 variations in code are available
3.13.3
high level coded actuator
coded actuator for which more than 1,000 variations are available
3.14
actuating system
part of the interlocking device which transmits the position of the actuator and changes the state of the output system
Example: Roller plunger, cam mechanism, optical, inductive or capacitive sensor.
Note: Examples of actuating systems are shown in Figure 2.
3.15
output system
part of the interlocking device that indicates the state of the guard to the control system
Example: Contact element (electromechanical), semiconductor output, valve.
3.16
type 1 interlocking device
interlocking device with mechanically actuated position switch with uncoded actuator
Example: Hinged interlocking devices.
Note: See Annex A for detailed examples.
3.17
type 2 interlocking device
interlocking device with mechanically actuated position switch with coded actuator
Example: Tongue-actuated position switches.
Note: See Annex B for detailed examples.
3.18
type 3 interlocking device
interlocking device with non-contact actuated position switch with uncoded actuator
Example: Proximity switches.
Note: See Annex C for detailed examples.
3.19
type 4 interlocking device
interlocking device with non-contact actuated position switch with coded actuator
Example: RFID tag actuated position switches.
Note: See Annex D for detailed examples.
3.20
stop command
signal generated by the interlocking device that causes the hazardous machine function to disappear
3.21
overall system stopping performance
time interval between the stop command given by opening the guard and the termination of the hazardous machine function
Note: It is revised from GB/T 19876-2012, Definition 3.1.2.
3.22
access time
time taken by a person to reach the hazard zone after initiation of the stop command by the interlocking device, as calculated on the basis of an approach speed of the body or part of the body
Note: For the selection of the approach speed and the calculation of the access time, see GB/T 19876.
3.23
holding force
force that a guard locking device can withstand without being damaged so that its further use will not be impaired and the guard will not leave the closed position
3.24
prevention of inadvertent locking position
feature of a guard locking device which ensures that the locking means (e.g. a locking bolt) cannot take the locked position when the guard is not closed
3.25
emergency release of guard locking
possibility to release manually without aids the guard locking from outside the safeguarded area in case of an emergency
Note: The guard locking with emergency release can be necessary for releasing trapped persons or fire-fighting, for example.
3.26
auxiliary release of guard locking
possibility to release manually by means of a tool or a key the guard locking from outside the safeguarded area in case of its failure
Note: The guard locking with auxiliary release is not suitable for emergency or escape release of guard locking.
3.27
escape release of guard locking
possibility to release manually without aids the guard locking from inside the safeguarded area to leave the area
3.28
guard locking for protection of a person
application of a guard locking device to protect a person against a hazard
3.29
guard locking for protection of the process
application of a guard locking device to protect the working process from being interrupted
3.30
tool
implement such as a key or wrench designed to operate a fastener
Note: An improvised implement such as a coin or a nail file cannot be considered as a tool.
[ISO 14120: 2002, Definition 3.9]
3.31
power interlocking
interlocking which directly interrupts the energy supply to the machine actuators or disconnects moving parts from the machine actuators
Note: Resumption of the energy supply is only possible with the guard in the closed and locked position. “Directly” means that, unlike control interlocking, the control system does not play any intermediate role in the interlocking function.
3.32
safety function
function of a machine whose failure can result in an immediate increase of the risk(s)
[GB/T 15706-2012, Definition 3.30]
4 Operating principles and typical forms of interlocking devices associated with guards
4.1 General
Interlocking techniques involve a broad spectrum of technological aspects. Interlocking devices may be classified using a great variety of criteria, e.g. the nature of the link between guard and output system, or the technological type (electromechanical, pneumatic, electronic, etc.) of the output system.
Interlocking devices have a guard position monitoring function that senses whether the guard is closed or not and produce a stop command when the guard is not in the closed position. An interlocking device may also be used in the control of other functions e.g. application of a brake to stop hazardous machine functions before access is possible. Some interlocking devices also have a guard locking function to keep the guard locked while hazardous machine function is present. A guard locking device status monitoring function monitors whether the guard locking device is locked or unlocked and produces an appropriate output signal [see 4.3.1a) and b)].
Note 1: The guard locking device (see 3.4) may be an integral part of an interlocking device, or a separate unit.
Note 2: See also GB/T 15706-2012, 6.3.3.1 for additional information on guards.
Note 3: The four types of interlocking device are not shown in Table 1 and presented in a hierarchical order. The correct application of each type of interlocking device will be dependent on the risk assessment that shall be made for the specific machine.
Table 1 shows the actuation principles and actuators for the defined interlocking device types.
Table 1 Overview of interlocking devices
Actuation principle examples Actuator examples Type Examples: see Annex a
Mechanical Physical contact/force Uncoded Rotating cam Type 1 A.1
Linear cam A.2, A.4
Hinge A.3
Coded Tongue (-shaped actuator) Type 2 B.1
Trapped-key B.2
Non-contact Inductive Uncoded Suitable ferric metal Type 3 C
Magnetic Magnet, solenoid
Capacitive Any suitable object
Ultrasonic Any suitable object
Optic Any suitable object
Magnetic Coded Coded magnet Type 4 D.1
RFID Coded RFID tag D.2
Optic Optically coded tag —
a Examples of other interlocking guards are given in Annex E.
Key:
1——movable guard; 4——position switch;
2——interlocking device; 5——actuating system;
3——actuator; 6——output system.
a Cam; c E.g. RFID, reflector, suitable surface;
b Tongue; d Movement direction.
Note: In some exceptional cases, the position switch can be installed on the movable guard and the actuator on the stationary part of the machine. In these cases, “1” is the stationary part of the machine.
Figure 2 Principle of types 1, 2, 3 and 4 interlocking devices
4.2 Principles of guard interlocking without guard locking
When guard interlocking function without guard locking is used, the guard can be opened at any time regardless of the function of the machine.
If the guard is not closed, the interlocking device shall generate a stop command.
Note 1: For interlocking with the machine control system, see Clause 8.
Note 2: Examples of interlocking devices without guard locking are shown in Annexes A, B, C and D.
Note 3: A functional diagram of interlocking devices without guard locking is shown in Figure 3.
Figure 3 Functional diagram of interlocking devices without guard locking
4.3 Principles of guard interlocking with guard locking
4.3.1 General
When interlocking with guard locking is applied, opening of the guard shall be prevented by a guard locking device (see 3.4) unless all hazardous machine functions covered by this guard have disappeared.
There are two alternatives for the design of the guard locking function (see Figure 4).
a) Unlocking of the guard can be initiated at any time by the operator. When unlocking is started, the guard locking device generates a stop command. This is called unconditional unlocking. The time necessary for the guard to be unlocked shall be greater than the time necessary for the hazardous machine function to disappear.
b) Unlocking of the guard is possible only when the hazardous machine functions have disappeared. This is called conditional unlocking.
Note: In conditional locking, the change from state 2 to state 3 or from state 3 to state 2 can happen without time delay.
Figure 4 Functional diagrams of interlocking devices with guard locking
Examples of guard locking devices are given in Annex F.
4.3.2 Interlocking device with mechanically operated guard locking
The mechanical part (e.g. bolt) which locks the interlocking guard may be:
——manually applied and manually released (see Figure F.5);
——spring (or similar) applied and power-ON released [see Figure 5a)];
——power-ON applied and spring (or similar) released [see Figure 5b)];
——power-ON applied and power-ON released [see Figure 5c)].
Mechanically operated guard locking shall use the principle of direct mechanical blocking due to form. Friction and force alone shall not be relied upon.
a) Spring applied Locking
Power-ON released Unlocking
b) Power-ON applied Locking
Spring released Unlocking
c) Power-ON applied Locking
Power-ON released Unlocking
d) Power-ON applied Locking
Power-ON released Unlocking
Figure 5 Operating modes of guard locking device in power-actuated guard locking devices
4.3.3 Interlocking device with electromagnetically operated guard locking
The guard is kept closed (locked) without any mechanical locking means by an electromagnetic force (see F.4).
The electromagnetic guard locking operates on the principle of power-ON applied and power-OFF released [see Figure 5d)].
5 Requirements for the design and the installation of interlocking devices with and without guard locking
5.1 General
Interlocking devices shall be installed in a suitable robust manner and in accordance with any instructions provided by the manufacturer (see Clause 9).
5.2 Arrangement and fastening of position switches
Position switches shall be arranged so that they are sufficiently protected against a change of their position. In order to achieve this, the following requirements shall be met:
a) fasteners of the position switches shall be reliable and loosening them shall require a tool;
b) type 1 position switches shall have provisions for permanently fixing the location after adjustment (e.g. by means of pins or dowels);
c) necessary means of access to position switches for maintenance and checking for correct operation shall be ensured. Prevention of defeat in a reasonably foreseeable manner shall also be considered when designing the access means;
d) self-loosening shall be prevented;
e) defeat of the position switch in a reasonably foreseeable manner shall be prevented (see Clause 7);
f) the position switch shall be located and, if necessary, protected so that damage from foreseeable external causes is avoided;
g) the movement produced by mechanical actuation or the gap of the proximity device actuating system shall remain within the specified operating range of the position switch or actuating system specified by the switch manufacturer to ensure correct operation and/or prevent overtravel;
h) a position switch shall not be used as a mechanical stop, unless this is the intended use of the position switch as declared by the manufacturer;
i) misalignment of the guard that creates a gap before the position switch changes its state shall not be sufficient as to impair the protective effect of the guard (for access to hazard zones, see ISO 13855 and ISO 13857);
j) the support and fastening for the position switches shall be sufficiently rigid to maintain correct operation of the position switch.
5.3 Arrangement and fastening of actuators
5.3.1 General
Actuators (see Figure 2) shall be so fastened to minimize the possibility that they come loose or change their intended position relative to the actuating system during the intended lifetime.
Note: A regular check can be necessary (see 9.3.2).
The following requirements shall be met:
a) fasteners of the actuators shall be reliable and loosening them shall require a tool;
b) self-loosening shall be prevented;
c) the position switch shall be located and, if necessary, protected so that damage from foreseeable external causes is avoided;
d) an actuator shall not be used as a mechanical stop, unless this is the intended use of the actuator as declared by the manufacturer;
e) the support and fastening for the actuators shall be sufficiently rigid to maintain correct operation of the actuator.
5.3.2 Cams
Rotary and linear cams for type 1 interlocking devices shall meet the following requirements:
a) they are fixed by fasteners requiring a tool for loosening them;
b) final fixing is achieved by form (e.g. spline or pin) or other methods that provide equivalent integrity of fixing;
c) they do not damage the position switch or impair its durability.
5.4 Actuation modes of interlocking devices
When a single type 1 or type 2 interlocking device is used to generate a stop command, it shall be actuated by direct mechanical action between guard, actuator and output system and the contact element shall have direct opening action (see 3.10, 3.11 and Table 2).
Non-direct mechanical action for a type 1 interlocking device shall be used only in conjunction with a type 1 or type 2 interlocking device with direct mechanical action between guard, actuator and output system. Combining one interlocking device with direct mechanical action with a second interlocking device with non-direct mechanical action avoids common cause failures (see 8.3).
Table 2 Direct and non-direct mechanical action of type 1 interlocking devices
Mechanical action Guard closed Guard not closed Working mode Example of behaviour in case of failure (see 8.3.2)
Direct Plunger held depressed by cam as long as guard is not closed.
When guard closed, output system changes, its state as result of action of return spring. Output system remains in safe state when guard is not closed even if spring breaks.
Non-direct The plunger is held depressed by a cam as long as the guard is closed.
When guard not closed, output system changes state as result of action of return spring. If spring breaks, output system can go to unsafe state even if guard not closed.
Interlocking devices shall be actuated appropriate to the actuation principle of the applied position switch.
If a type 3 or type 4 interlocking device is the only interlocking device, it shall meet the requirements of IEC 60947-5-3.
5.5 Interface to control systems
The output system of interlocking devices shall be suitable for inclusion in a control system designed in accordance with GB/T 16855.1 or IEC 62061.
5.6 Mechanical stop
If an interlocking device is declared by the manufacturer of the device to be suitable for use as a mechanical stop the maximum impact energy withstand value shall be given [see also 9.2.2 r)].
5.7 Additional requirements on guard locking devices
5.7.1 General
If the application of the guard locking function creates hazards, additional measures shall be considered (see 5.7.5 and GB/T 15706-2012, 6.3.5.3).
The locking element (e.g. bolt) intended to lock the guard shall be “spring applied – power-ON released” [see Figure 5a)] or “power-ON applied – power-ON released” [see Figure 5c)] unless the outcome of the risk assessment shows that this is not appropriate. If other systems [e.g. Figure 5b)] are used in a specific application, they shall provide an equivalent level of safety.
Note: When the loss of power results in the release of the locking element, the stopping time of the machine is often lengthened considerably and it can be possible to access to the hazard before the movements have been stopped (or other hazards disappeared).
The requirements of 5.7 apply when guard locking function is used for the protection of persons. While the requirements of 5.7 do not apply when guard locking function is used solely for the protection of a process. Nevertheless, if guard locking function and guard interlocking function are part of the same device the safety level of the guard interlocking function shall not be negatively affected by a non safety related guard locking function (i. e. guard locking function used solely for the protection of the process).
The requirements of 5.7 apply to both guard locking devices composed of separate components as well as to guard locking devices which form an integral part of an interlocking device with guard locking. They apply to all technologies.
The guard locking device shall allow the locked position to be monitored by providing an output system compatible with a control system designed in accordance with GB/T 16855.1 or IEC 62061.
The guard locking device shall only allow hazardous functions of the machine when the guard is closed and locked.
5.7.2 Mechanical guard locking device
5.7.2.1 General
Mechanically operating guard locking shall result from the engagement of two rigid parts [form closure, see Figure 5a) to c)].
If it is foreseeable that access is necessary in case of emergency, for “spring applied – power-ON released” or “power-ON applied – power-ON released” systems [see Figure 5a) and c)], a guard locking device with emergency release (see 5.7.5.3) shall be provided.
Figure 6 shows the functionality of such a device.
5.7.2.2 Locking monitoring
The locked position of the locking element shall be monitored in accordance with the requirements of 5.5.
The hazardous function of the machine shall only be possible when the monitoring detects the closed position of the guard and the locked position of the locking element (see Annex F).
For an effective monitoring of the guard locking device, one of the following methods shall be ensured:
——the locking element can only go in the locked position if the movable guard is in the closed position (see Figure 6), in that case the closed position and the locking of the guard can be checked by the monitoring of the locking element;
——in the other case, the monitoring of the locking element and additionally the monitoring of the guard position shall be used for interlocking.
Key:
a)——guard closed and locked; 1——actuator (tongue);
b)——guard closed and not locked; 2——locking element (bolt);
c)——guard not closed and not locked; 3——actuating system (internal rotating cam).
Note: In this kind of position switch, the actuator has two functions: to operate the contacts (not shown in the figure) and together with the internal rotating cam and the bolt to provide the guard locking function. The bolt may be operated by external means e.g. a solenoid or pneumatic cylinder.
Figure 6 Example of type 2 interlocking device with guard locking
5.7.3 Electromagnetic guard locking device
5.7.3.1 General
The force required for the locking of the guard is applied by the generation of an electromagnetic field [see Figure 5d)].
5.7.3.2 Locking monitoring
The holding force shall be monitored to determine if the specified holding force has been achieved and maintained (see 6.2.2 and Annex I).
The hazardous function of the machine shall only be possible when the monitoring detects the closed position of the guard and the achievement of the specified holding force.
5.7.3.3 Basic measures for minimizing defeat possibilities
If an electromagnetic guard locking device is opened by force, it shall be ensured that the process cannot be immediately continued.
Note: In contrast to a mechanical guard locking, an electromagnetic guard locking shows no damage after an opening by force.
The objective of the measure is that an opening by force results in a time expenditure which is similar to that of repair works (time delay) and comparable with the repair of a damage of an electromechanical guard locking.
Contents of GB/T 18831-2017
Foreword i
Introduction iii
1 Scope
2 Normative references
3 Terms and definitions
4 Operating principles and typical forms of interlocking devices associated with guards
4.1 General
4.2 Principles of guard interlocking without guard locking
4.3 Principles of guard interlocking with guard locking
5 Requirements for the design and the installation of interlocking devices with and without guard locking
5.1 General
5.2 Arrangement and fastening of position switches
5.3 Arrangement and fastening of actuators
5.5 Interface to control systems
5.6 Mechanical stop
5.7 Additional requirements on guard locking devices
6 Selection of an interlocking device
6.1 General
6.2 Selection of a guard locking device
6.3 Environmental conditions considerations
7 Design to minimize defeat possibilities of interlocking devices
7.1 General
7.2 Additional measures to minimize defeat possibilities of interlocking devices
8 Control requirements
8.1 General
8.2 Assessment of faults
8.3 Prevention of common cause failures
8.4 Release of guard locking device
8.5 Fault exclusion
8.6 Logical series connection of interlocking devices
8.7 Electrical and environmental conditions
9 Information for use
9.1 General
9.2 Information for use given by the manufacturer of interlocking devices
9.3 Information for use given by the manufacturer of the machine
Annex A (Informative) Type 1 interlocking device — Examples
Annex B (Informative) Type 2 interlocking device — Examples
Annex C (Informative) Type 3 interlocking device — Examples
Annex D (Informative) Type 4 interlocking device — Examples
Annex E (Informative) Examples of other interlocking devices
Annex F (Informative) Example of guard locking devices
Annex G (Informative) Application examples of interlocking devices used within a safety function
Annex H (Informative) Motivation to defeat interlocking device
Annex I (Informative) Examples for maximum static action forces
Bibliography
