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Operation of enabling switches
The requirement for operation of 3-position enabling
switches (according to IEC 60204-1; 9.2.5.8):
When an enabling device is provided as a part of a
sys tem, it shall be designed to allow motion when
actuated in one position only. In any other position
motion shall be stopped.
– for a three-position type:
• position 1: off-function of the switch
(actuator is not operated)
• position 2: enabling function
(actuator is operated in its mid position)
• position 3: off-function
(actuator is operated past its mid posi-
tion)
When returning from position 3 to position 2, the
function shall be ended.
Disparity detection of two contacts
• A high level of safety—safety category 3 or higher (ISO 13849-
1)—is required when an operator works near a hazard inside a
safety guard.
When released to position 1, the contacts are opened (turned
off) by the force of a released spring. The 3-position enabling
switches must be prepared for failures such as contact welding
and short-circuits, and a dual circuit is provided. Even if one
contact fails, the remaining contact can disable machine
operation. Furthermore, a disparity detection circuit is provided
so that machine operation is disabled when a disparity between
the two circuits is detected using a safety relay module.
International standards on enabling switches
IEC 60204-1: 1997
9.2.4
Where it is necessary to suspend safeguarding, (e.g.
for set ting or maintenance purposes), a mode selection device
or means capable of being secured (e.g. locked) in the desired
mode shall be provided so as to prevent automatic operation. In
addition, one or more of the following means shall be provided:
- a portable control station (e.g. pendant) with an emergency stop
device and, where appropriate, an enabling device. Where a
porta ble station is in use, motion may be initiated only from that
station.
ISO 12100-2: 2003
Control mode for setting, teaching, pro-
cess changeover, fault-finding, cleaning or maintenance
4.11.9 Where, for setting, teaching, process changeover, fault-
find ing, cleaning or maintenance of machinery, a guard has to
be dis placed or removed and/or a protective device has to be
disabled, and where it is necessary for the purpose of these
operations for the machinery or part of the machinery to be put in
operation, safety of the operator shall be achieved using a specific
control mode which simultaneously:
- permits operation of the hazardous elements only by continuous
actuation of an enabling device, a hold-to-run control device or a
two-hand control device.
ANSI/RIA R15.06
The pendant or teaching control device shall have an enabling
device using a three position switch which, when continuously
held in a detented position, permits motion. Release of or
compression past the midpoint detent of the device shall stop
robot motion using cir cuitry consistent with 4.5.
Note: Tests have shown that human reaction to an emergency may be to
release an object, or hold on tighter, thus compressing an enabling
device. Design and installation of the enabling device should
consider the ergonom ics issues of sustained activation.
ANSI B11.19, 12.3.1.3
Enabling devices shall be designed and constructed to permit
limited and supervised machine motion while personnel are inside
a hazard area.
Position 1
1. Press lightly
Position 2
3. Press tightly
Position 3
Terminal Contact
Movable Contact
Disparity Detection Circuit
for Dual Contacts
2-circuit
input
Enabling
Device
L (+)
24V DC
F1
External
Start Condition
A1
HR1S-AF
Safety Relay Module
A2
S1
Enabling
Switch
N (–)
A method of changing an operation mode (auto/
manual) using the HS5B interlock switch and grip
style enabling switch (HE1G)
Enabling switch is
attached to the interlock
switch— machine
operates auto matically.
OFF
2. Release
ON
OFF
Machine can
Both ON
operate (normal)
Agree
Machine cannot
Both OFF
operate (normal)
Disagree
Machine cannot
One ON, the
operate (failure of
other OFF
enabling switch,
machine cannot
restart)
ESC
S33
S34
13
23
S11
S12 S21 S22
14
24
Safety Output
Enabling switch is
detached from the inter-
lock switch—machine
can be operated only
manu ally.
4. Release
33
34
3
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