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Functional description
3-position principle
A 3-position switch provide signals that:
when enabled, allow a machine or other device to start from a separate start controller, and
when disabled, initiates a stop function and prevents the machine or equipment from starting.
A 3-position switch can also be used as a "hold-to-run" device. When it is used in this way, a machine can be run at
the same time as a protected area can be accessed. One way of achieving this is by pressing in the 3-position
button to the midpoint position (ON) and remove it from the holder with a proximity sensor, which in turn causes
another safety device (light guard, interlock switch etc.) to be bypassed which means the protected area can be
accessed without stopping the machine. Certain limitations of times, speeds, etc. may be necessary to achieve an
acceptable level of safety.
Two 3-position switches are used and controlled simultaneously to create a two-channel safety system.
The three positions are indicated as follows:
Position 1: The connector is in the OFF position (the button is not pressed)
Position 2: The connector is in the ON position (the button is pressed to normal operating position)
Position 3: The connector is in the OFF position (button is fully depressed)
When you release the button, it will always return to position 1, regardless of whether it was in position 2 or 3. The
connectors are kept open during the entire movement.
In addition to the safety function that is enabled by the 3-position buttons, JSHD4 can also be fitted with other
extensions such as push buttons for selectable functions (start, stop, grippers, etc.), emergency stop or an anti-
cheat-board.
The anti-cheat unit
Many variants of JSHD4 can be fitted with a sensor that prevents improper use of the actuator (e.g., by keeping the
3-position buttons in the ON position using a rubber band or similar). The sensor detects a human hand and the
small movements/vibrations that are natural when a handle is being held in one hand. As long as both of these
requirements are met (detected) a connector will close. With a proper connection, the connector can be used to
break the safety circuit and consequently prevent misuse.
2TLC172072M0201, rev. F
2018-06-01
The symbol for the 3-position switch shows the three positions (OFF, ON, OFF)
with O and I, actuating force from left to right, and possible paths for the switch
(IEC 60947-5-8:2006).
An important feature of a 3-position switch is that when it returns from position
3, the ON position is never reached – the connectors are kept open.
6
www.abb.com/jokabsafety
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