SAFETY SWITCH FOR AN INDUSTRIAL MACHINE

Abstract: The invention relates to a safety switch intended to be connected into a safety circuit for an industrial machine, for example an industrial robot. The switch comprises a contact device (2) with a hand-operated device (3, 4) in which a pressure rod (31) is displaceable against the action of a return spring (33) from a first end position via an operating position to a second end position, the safety circuit being closed only in the operating position. During the return movement of the pressure rod from its second to its first end position, the contact device (2) is not affected, and the safety circuit thus remains open during the whole of this return movement.

Description: Safety switch for an industrial machine TECHNICAL FIELD The present invention relates to a hand-operated safety switch of the kind described in the preamble to claim 1. The safety switch is primarily intended to be used in applica¬ tions in the engineering industry, for example in an indus¬ trial 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 con¬ trolled 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 un¬ reasonably 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 pro- cedure 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 opera- ting 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 inopera¬ tive. 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 loca¬ ted 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 posi¬ tion. 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 ove- ments 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 inven¬ tion 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 opera- ting position to a second 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 opera- ting 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 descri- bing an embodiment with reference to the accompanying draw¬ ings, wherein Figure 1 is a side view of a safety switch according to the invention in its initial position (first end posi- tion) , Figure 2 shows the switch in the same position in a view from above, Figures 3 and 4 are side views of the switch in its opera¬ ting position (mid-position) and in its second end position, respectively, Figures 5, 6 and 7 show the housing of the switch in a view from the side (Fig. 5) , in an end view from the left (Fig. 6), and in a view from above (Fig. 7), respectively, Figures 8 and 9 show a pressure rod, included in the opera- ting member of the switch, in a side view and in an end view from the left, respectively, and Figures 10 and 11 show a lever arm, included in the switch, in a side view and a view from the left, respec- tively. DESCRIPTION OF THE PREFERRED EMBODIMENT The safety switch shown in Figure 1 comprises a housing 1, in the upper part of which a microswitch 2 is fixed and in the lower part of which an operating member 3 in the form of a pressure rod 31 with a pressure plate 32 is journalled so as to be longitudinally displaceable. Between the pressure plate 32 and the housing 1, a compression spring (return spring) 33 is arranged. The microswitch 2 comprises at least one contact pair with one fixed and one movable contact 21 and 22, respectively. With the aid of an actuating member 23, the movable contact 22 may be displaced from the open position shown in Figure 1 to the closed position shown in Figure 3. The movable contact is permanently influenced by a return spring 24 in a direction towards the open position. The transmission of the operating force from the operating member 3 to the microswitch 2 is achieved by a lever arm 4 which, with the aid of a cylindrical pin 41, is rotatably journalled in the housing 1. In the lower part of the lever arm 4 there are a compression spring 42 and a ball 43. The spring-loaded ball 43 presses against the pressure rod 31, which is provided with a recess 36 (Fig. 4) , arranged at that end of the rod which is located furthest away from the pressure plate 32 and cooperating with the ball 43, for achieving a coupling engagement between the pressure rod and the lever arm. The upper end portion of the lever arm makes contact with the actuating member 23 of the microswitch. As is clear from Figures 5-7, the housing 1 of the safety switch is provided, in its upper part, with fixing holes 11 for the microswitch 2 and, in its lower part, with a bearing hole 12 with guide slots 13 for the pressure rod 31. The centre lines of the holes 11, 12 are parallel. Between the orifices of the holes 11, 12 on one side of the housing 1, two parallel wall portions 14, 15 extend, between which the lever arm 4 is intended to be mounted. The wall portions are provided with through-holes 16 for the bearing pin 41 of the lever arm. Further, the housing 1 is provided with two fixing holes 17 for fixing the safety switch in, for example, a programming box for an industrial robot. The pressure rod 31, which is shown separately in Figures 8 and 9, has a substantially circular cross section and is provided at one end with an axial hole 34 for fixing the pressure plate 32. At its other end the pressure rod is provided with a recess which, nearest the end surface of the rod, is made with a deeper portion 36 which forms a seat for the ball 43 and which, via a shoulder 37, changes into a shallower portion 38 which forms a rolling or sliding path for the ball 43. The height of the shoulder is considerably smaller than the diameter of the ball, for example about 1 mm if the diameter of the ball is 4 mm. The shoulder can suitably be made inclined so as to obtain a more even transition between the two portions 36 and 38. In the embo- diment shown the shoulder 37 forms an angle of about 45° with the longitudinal axis of the pressure rod. The pressure rod 31 is provided with radially projecting guide pins 39 which fit into the guide slot 13 of the housing. The pins 39 limit the axial movement of the pressure rod in a direction towards the right to the end position shown in Figure 1 and also prevents the rod from moving in the direction of rotation. The lever arm 4 is shown separately in Figures 10 and 11. It has a transversal hole 44 for the bearing pin 41 as well as a longitudinal hole 45 for accomodating the compression spring 42 and the ball 43. The centre lines of the holes 44, 45 are directed perpendicularly to each other. At the orifice of the hole 45, there is a transversal hole 46 for temporary insertion of a mounting pin to keep the compress¬ ion spring 42 and the ball 43 fixed in the hole 45 during mounting. The pressure rod 31 is suitably made of a plastic material, for example acetal plastic, whereas the other parts, such as the housing 1 and the lever arm 4, are suitably made of metal. The safety switch operates as follows: In the initial posi¬ tion shown in Figure 1, the spring 33 keeps the pressure rod 31 in its first end position, and the spring 24 built into the microswitch keeps the switch in the open position, whereby the safety loop into which the switch is connected is open. By pressing on the pressure plate 32, the pressure rod 31 is pressed in and influences the lever arm 4 which, in its turn, presses the actuating member 23 of the microswitch into the operating position shown in Figure 3, in which the safety loop is closed. In normal operation, the movement on the pressure rod takes place between the initial position according to Figure 1 and the operating position according to Figure 3. When in the operating position according to Figure 3 and an emergency situation arises, the pressure plate can either be released or be pressed in further. In the latter case, an increased pressure is required for the ball 43 to pass the shoulder 37 between the deeper portion 36 and the shallower portion 38 on the pressure rod. This increased pressure is determined by the spring 42. When the ball has arrived on the shallower portion 38 of the pressure rod, the lever arm 4 is disengaged from the pressure rod and the microswitch can return to its open position while being influenced by the return spring 24, while continuing the pressing of the pressure rod until the rod has reached its second end posi¬ tion according to Figure 4. Also in this end position, the safety loop is thus open. To get from the second end posi¬ tion according to Figure 4 to the first end position (ini- tial position) according to Figure 1, the pressure plate 32 is released and the switch resumes the initial position with the aid of the spring 33. During the return movement of the pressure rod from the second to the first end position, the microswitch 2 is not influenced, and the safety loop is thus open during the whole return movement. A considerable advantage with the described switch design is that no adjustment is required when mounting the switch. The invention is not limited to the embodiment shown but several modifications are possible within the scope of the claims.

Claims: CLAIMS 1. A safety switch for an industrial machine, intended to be connected into an emergency stop circuit for the machine and comprising a contact device (2), mounted in a housing (1), with a hand-operated device (3, 4) for switching the contact device between an open position, in which the safety switch is open, and a closed position, in which the safety circuit is closed, the contact device comprising a spring (24) for permanently influencing the contact device in a direction towards the open position, characterized in that the hand-operated device (3, 4) comprises a pressure operating member (31) which is displaceable against the action of a return spring (33) from a first end position (Fig. 1) via a mid-position (Fig. 3) to a second end position (Fig. 4) , the pressure operating member (31) being connected to the contact device (2) in such a way that the contact device assumes the open position when the operating member is in its end positions and the closed position when the operating member is in its mid-position, and that the contact device (2) is not influenced by the operating member (31) when this member returns from its second to its first end position. 2. A safety switch according to claim 1, characterized in that the hand-operated device (3, 4) comprises a lever arm (4), rotatably journalled in the housing, for transmitting operating force from the pressure operating member (31) to the contact device (2), the lever arm making contact at one of its end portions with the operating member (31) and at its other end portion with an actuating member (23) asso¬ ciated with the contact device. 3. A safety switch according to claim 2, characterized in that that end portion of the lever arm (4) which makes contact with the pressure operating member (31) exhibits a resilient member (42, 43) . 4. A safety switch according to claim 3, characterized in that the resilient member comprises a ball (43) which is pressed by a compression spring (42) against a side surface of the pressure operating member (31) . 5. A --afety switch according to claim 3 or 4, characterized in that the pressure operating member (31) is provided with a recess (36) which is adapted such that, together with the resilient members (42, 43) of the lever arm, it brings about a coupling engagement between the ope¬ rating member (31) and the lever arm (4) during the dis¬ placement of the operating member from its first end posi¬ tion to its mid-position, but which, during continued dis¬ placement of the operating member (31) from the mid-position towards the second end position, permits the resilient mem¬ ber (42, 43) to be pressed out of the recess (36), the lever arm (4) thus being disengaged from the operating member (31). 6. A safety switch according to any of the preceding claims, characterized in that the pressure operating member (31) comprises a pressure rod which is longitudinally displaceable in a bearing hole (12) arranged in the housing (1), the rod (31) being provided with transversally projec- ting guide pins (39) which are in engagement with guide slots (13), arranged in the housing, for limiting the return movement of the rod and for fixing the rod in the direction of rotation. 7. A safety switch according to any of claims 4-6, characterized in that the recess in the pressure rod comprises a deeper portion (36) which is provided at one end of the pressure rod (31) and which forms a seat for the ball (43) and which, via a shoulder (37), changes into a shallower portion (38) which forms a rolling or sliding path for the ball (43) . 8. A safety switch according to any of the preceding claims, characterized in that the contact device (2) consists of a microswitch.

Inventors: GUNNARSSON SVEN-ERIC, GUNNARSSON, SVEN-ERIC
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1992
Main classification: F16P3
IPC codes: B25J19, F16P3, G05G1, H01H3, H01H13