Electricity: circuit makers and breakers – Solid contact – Bimodal
Patent
1994-04-20
1995-08-22
Luebke, Renee S.
Electricity: circuit makers and breakers
Solid contact
Bimodal
H01H 1350
Patent
active
054442036
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hand-operated safety switch for an industrial machine, intended to be connected with an emergency stop circuit for the machine. The safety switch is primarily intended to be used in applications in the engineering industry, for example in an industrial robot application where persons are present within the operating range of the robot.
BACKGROUND ART
An industrial robot can be controlled with the aid of a joystick. During a teaching or programming procedure, the position and/or orientation of the robot tool can be controlled in the desired manner by means of the joystick. The joystick can either be arranged on a fixed control cabinet or on a smaller, separate programming unit, which during programming or teaching can be held in the hand or be placed on a table. In order that programming shall not take an unreasonably long time, it is necessary that a full deflection of the joystick causes a movement with a relatively high speed of response in the robot. During the teaching procedure it may be necessary for personnel to stay in the vicinity of the robot in order to eliminate the risks of injuries which arise in this connection, a safety plate is arranged on programming units of the above-mentioned kind, on which safety plate the operator's hand rests when operating the joystick with the aid of the fingers. When the hand is removed, the safety plate senses this and influences the control system such that the joystick is rendered inoperative. In this way, it is prevented that an unintentional contact with the joystick gives rise to a movement of the robot. A device of this kind is described in Swedish printed patent application 450 285 and in Asea Journal 1982, No. 6, pp. 145-150.
In the known device there may be a certain risk that the operator, in an emergency situation, reacts incorrectly and instead of removing his hand from the safety plate presses even harder, whereby the robot continues its movement with an ensuing risk of both material damage and personal injury. To avoid this it has been proposed to use a contact device, actuated by the safety device, with two end positions located on different sides of an operating position, one of the end positions constituting the initial position (the rest position) and the other end position an extra neutral position. A drawback with this design, however, is that the contact device while returning to the initial position has to pass the operating position, whereby the safety circuit is briefly closed with an ensuing risk of uncontrolled movements of the robot.
SUMMARY OF THE INVENTION
The present invention aims to provide a safety switch designed for the above-mentioned field of use, which does not suffer from the above-mentioned drawbacks of comparable prior art designs. This is achieved according to the invention by a safety switch with the characteristic features stated in the claims.
The safety switch according to the invention comprises a contact device with a hand-operated device in which a pressure operating member is displaceable against the action of a return spring from a first end position via an operating position to a seconded end position, whereby the safety circuit, into which the switch is intended to be connected, is connected only in the operating position. The operating device is arranged such that the contact device is not affected during the return movement of the pressure operating device from its second to its first end position, and thus the safety circuit remains open during the whole of this return movement.
A safety switch according to the invention makes it possible for industrial machines of the above-mentioned kind to be installed, used and maintained with an adequate degree of safety against personal injury. In addition, the switch is simple to manufacture and mount.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail by describing an embodiment with reference to the accompanying drawings, wherein
FIG. 1 is a side view of a safety switch ac
REFERENCES:
patent: 2616009 (1952-10-01), Roeser
patent: 2919333 (1959-12-01), Scholin et al.
patent: 3118206 (1964-01-01), Bush
patent: 3384725 (1968-05-01), Poch
patent: 3674970 (1972-07-01), Bendocs
patent: 4450331 (1985-05-01), Fukukura
Asea Brown Boveri AB
Luebke Renee S.
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