This invention relates to safety switch assemblies used especially but not exclusively in machinery guards enclosing kinetic machinery.

Safety switch assemblies are known which are adapted to be fitted to an enclosure having a door, gate or protective cover, the switch assembly being adapted to switch OFF and electrical power supply when the door, gate or protective cover is opened.

These known safety switch assemblies comprise a safety- switch adapted to be fitted to the enclosure and an actuator adapted to be fitted to the door, gate or protective cover and insertible into the safety switch to turn ON the electrical power supply when the enclosure is closed by the door, gate or protective cover.

According to the present invention there is provided a safety switch comprising a housing, an electrical contact arrangement contained within the housing, a rotatable actuator cam also contained within the housing for operating the electrical contact arrangement and spaced from the electrical contact arrangement, radial pocket means formed in the actuator cam and extending inwardly of the periphery of the latter, axially-movable rod means connecting the electrical contact arrangement and the actuator cam to operate the former in accordance with rotational movement of the latter, the housing defining entry means adjacent the actuator cam for insertion of an actuator into the housing to engage the radial pocket means to rotate the actuator cam, anti-rotational locking means releasably engaging the actuator cam to prevent rotation of the latter and consequent operation of the electrical contact arrangement until a separation of the actuator cam and the anti-

rotational locking means is effected by the actuator, and solenoid-operated claw means disposed alongside the actuator cam for engaging a locking formation of the actuator to secure the actuator in engagement with the actuator cam to maintain the electrical contact arrangement in a power supply ON condition.

Preferably the actuator comprises laterally-spaced limbs means (i) insertible between the actuator cam and the anti- rotational locking means axially to space same apart, and (ii) engagable with the actuator cam to rotate same axially to move the rod means to operate the electrical contact arrangement, and a locking formation engagable by the solenoid-operated claw means to secure the actuator in engagement with the actuator cam to maintain the electrical contact arrangement in the power supply ON condition.

Also according to the present invention there is provided a safety switch assembly comprising the safety switch in combination with the actuator as both hereinbefore defined.

The present invention also includes w ^τ ithin its scope the ^" actuator per se.

As a result of this invention there is provided a safety switch assembly having both a tamper-resistant, operating cam arrangement, and a solenoid-operated lock ensuring the actuator is secured in position and thereby closure of, for example, the gate of a machinery guard to which the safety switch assembly is fitted.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1. is a front view of the safety switch assembly with the actuator in position;

Fig. 2. is a sectional view of the safety switch on the line II-II of Fig. 1;

Fig. 3. is a sectional view of the safety switch on the line III-III of Fig. I;

Figs. 4 and 5 are perspective views of alternative forms of the safety switch;

Fig. 6 is a perspective view of the actuator;

Fig. 7 is a side view of the locking claw means and a perspective view of the cam arrangement; and

Fig. 8 is a circuit diagram of the safety switch;

The safety switch assembly comprises two components, namely the safety switch A which contains an electrical contact arrangement B, an operating cam arrangement C, a connecting rod arrangement D as will be described hereinafter, a solenoid E, a locking claw F and an actuator G which operationally cooperates with the safety switch A also as hereinafter described.

The safety switch A comprises a heavy duty die cast alloy casing 10.

The casing 10 defines an electrical contact and solenoid containing compartment 11 at one end and, at its other end, has two parallel laterally-spaced walls 12, 12A for mounting the cam arrangement C which will be described in detail later. The wall 12A has parallel therewith a bearing plate 13, and

the locking claw F is pivoted therebetween.

The contact compartment 11 is open to the front of the casing 10 and is closed by a faceplate 14 removable to permit access to the contact arrangement B and the solenoid E.

Three conduit entry ports 15 to 17 are provided for passage of a conduited electrical cable (not shown) into the contact compartment 11 for securement to the contact arrangement B. Conduit entry ports 15 and 16 are disposed one at each side of the casing 10 while the conduit entry port 17 is disposed at what for convenience will be called hereinafter and in the claims the top of the casing 10. Each entry port 15 to 17 is normally closed by a plug as shown, a selected one of which is removed for entry of the conduited electrical cable depending upon the disposition of the safety switch casing 10 relative to the conduited electrical cable.

The contact arrangement B (see Fig. 8) comprises one set of double positive break, normally-open safety contacts 18, 19 and one set of double positive break, normally-closed auxiliary contacts 20, 21.

Contacts 18 and 21 and fixed contacts 19 and 20 are movable and are carried by a push rod 22 extending into a contact housing.

A plate 23 is fixed to the push rod 22 adjacent the bottom thereof and a compression spring 24 surrounding a bellows 25 acts between this plate 23 and a wall 26 of the housing 10 to keep the push rod 22 in the position diagra matically shown in Fig. 8, i.e. electrical power supply OFF.

The plate 23 is provided with a rod 23A pointing to the bottom of the safety switch A.

The making of contacts 18, 19 and the breaking of contacts 20, 21, and vice versa, is effected by

the axial push rod 22 and associated compression spring 24 and the cam arrangement C to which the push rod 22 is connected as later described.

Each of the walls 12, 12A on its outer face, is formed with a hole.

The cam arrangement C comprises two anti-tamper locking cams 27 between which is sandwiched an actuator cam 28. The cams 27 and 28 are mounted on a spindle 29 supported at its ends in the holes in the walls 12, and which extends through a central hole 27A in each of the locking cams 27.

Each of the latter is constrained against rotational movement about the shaft 29 but is axially movable along the latter. Each locking cam 27, on its face adjacent to the inner face of the adjacent wall 12, 12A is formed with an annular recess 29 in which engages one end of a compression spring 30, the other end of which bears against the inner face of the adjacent wall 12, 12A.

Each locking cam 27 is of circular disc-like configuration with flattened peripheral sides 27B, that is, two pairs of diametrically-opposed flat sides 27B

These flat sides 27B cooperate with inwardly- projecting pins 31 of an end cap 32, which pins 31 are disposed above the locking cams 27 to resist rotation of the latter about the shaft 29. The end cap 32 is detachable and encloses the locking hook F and the cam arrangement C.

The face of each locking cam 27 adjacent the actuator cam 28 has three relatively normally-spaced depressions 33 radiating inwardly towards the central hole from a flattened side 27B, that is one depression 33 to each of three adjacent quadrants of the locking cam 27. The fourth quadrant is pierced

by a hole 27C smaller in diameter than the central hole, the axes of the holes being parallel and lying in the same diameter of the locking cam 27.

The actuator cam 28 is axially substantially thicker than the locking cams 27, is generally of circular configuration, and is rotatable about the shaft 29. The actuator cam 28 is peripherally split to a diameter at substantially half its area to define a forked configuration 34, whereof the limbs 35 are bridged by a pin 36 extending through arcuate cam slots 37 formed in the limbs 35 and projecting outwardly of opposed faces 38 of the actuator cam 28 to engage in the holes 27C of the locking cams 45.

The pin 36 is fixed in the rod 23A and projects from both sides through the arcuate cam slots 37, the pin 36 resting normally in a central depression 37A of each arcuate cam slot 37. The pin 36 acts both as a locking pin and a cam follower pin.

The other half of the actuator cam 28 comprises a wall 39 centrally disposed relative to the axis of the actuator cam 28 and separating axially, to each side thereof, a pair of radial cut-outs or pockets 40 or 40A open to the periphery of the actuator cam 28, extending inwardly towards the spindle 29, and spaced angularly one to another. The spindle 29 extends through a central hole 41 in the actuator cam 28.

The pockets 40, 40A of the actuator cam 28 are normally open to the bottom of the safety switch.

The end cap 32 is formed at one corner with either a rectangular opening 42 to define a front actuator entry, or is formed with a cut-out 43 to define an end actuator entry. Both front and end actuator entries 42, 43 may be provided.

Each actuator entry 42, 43 is aligned with a respective pair of pockets 40, 40A of the actuator

cam 28.

The locking claw F is pivoted, as aforesaid between the wall 12A and the bearing plate 13 as shown at 44 (see Fig. 7). It has two locking claw formations 45, 46, each accessible through the front actuator entry 42 and the end actuator entry respectively.

The solenoid actuating rod 47 has a forked end 48 secured to the locking claw F adjacent its pivot 44. Operation of the solenoid E pivots the locking claw F as indicated by the arrow 49 as a result of axial movement (see arrow 50) of the solenoid operating rod 47.

The other component of the safety switch, namely the actuator G is formed, for example of stainless steel. It comprises a securing bar 51 formed with screw holes 52, one adjacent each end, for receiving securing screws (not shown), and projecting from the front face of the securing bar 51 is a plate 53 having a leading ϋ-shaped formation 54, whereof each limb 55 is inturned as indicated at 56.

The plate 53 is formed alongside but rearwardly of the forked formation 54 with a rectangular hole 57.

The abovedescribed safety switch A, G can be used, inter alia, in connection with machinery guards, the safety switch A being mounted on the guard housing and the actuator G on the guard gate or door which may be hinged, slidable or of lift-off construction.

The electrical circuitry, well known to those skilled in the art of providing electrical interlocks between kinetic machinery and machine guards therefor, is inhibited until the safety contacts 18, 19 are closed and the auxiliary contacts 20, 21 are

opened. The latter are signal contacts indicating the condition of the kinetic machinery and the machine guard in either condition, that is contacts 18, 19 closed indicates machinery in operation and machine guard closed, contacts 20, 21 open indicates machine guard open and machinery stopped.

With the contacts 13, 19 closed and contacts 20, 21 open, the solenoid E operates to pivot the locking claw F to engage the appropriate claw formation 45, 46 in the hole 57 in the actuator G thus locking the latter into the safety switch A.

The electrical circuitry of the safety switch is shown in Fig. 8, the mechanical link between the solenoid F and an interlock microswitch 60 being indicated at 61.

Inadvertent or unauthorised rotation of the cam arrangement C is prevented or resisted by abutment of the spring-loaded locking cams 27 and the pins 31 the engagement of the locking cams 27 via the holes 27C with the fixed locking pin 36, and the location of the latter within the depressions 37A of the arcuate cam slots 37 formed in the limbs 35 of the actuator cam 28.

When the guard door or gate is closed, the actuator G enters the appropriate entry 42 or 43. The limbs 55 of the actuator G engage simultaneously in the appropriate pockets 40 or 40A of the actuator cam 28 and between the actuator cam 27 and the locking cams 27 which forces the latter axially away from the actuator cam 28 along the spindle 29. This action causes compression of the springs 30, the locking cams 27 to disengage from the locking pin 36, and the actuator limbs 55 to engage in a pair of the opposed depressions 33 in the faces of the locking cams 27 adjacent the actuator cam 28. At the same

time, the latter is rotated causing one of the pairs of cam surfaces 37B at one side of the central depressions 36A to act on the locking pin 36, which now acts as a cam follower pin, to urge the plate 23 and consequently the axial push rod 22 to move axially against the action of the spring 24 to open the auxiliary contacts 20, 21 and close the safety contacts 18, 19, which condition will prevail as long as the actuator G is so engaged in the safety switch A.

Upon contact re-arrangement as described the solenoid E is energised to pivot the locking claw F to engage in the opening of the actuator G and secure it in position within the safety switch A. Only then is there a circuit made to enable the machine to start.

Retraction of the actuator E out of the safety switch A causes reversal of the contact conditions, that is contacts 23, 24, open and contacts 25, 26 close.

Such retraction and machinery guard door release can only be effected if the solenoid E receives a signal to indicate that the kinetic machinery being guarded has stopped or, if being employed, that the C.N.C. cycle is finished.

If the gate or door of the machinery guard is open only slightly, say, for example, 6mm this will force disconnection of the safety contacts 18, 19 in the event of contact weld and safety switch component failure thus providing complete operator safety.

Additionally, the auxiliary signal contacts 20, 21 will then be closed instantaneously, to all intents and purposes, indicating the condition of the machinery guard.

It is to be noted that both sets of contacts 18,

19 and 20, 21 are galvanically isolated thus eliminating the possibility of voltage cross-over.

An alternative contact arrangement (not shown) comprises two pairs of double positive break, normally-open contacts for use in dangerous or low voltage applications. In this arrangement it is to be noted that both the safety normally-open contacts and the auxiliary normally-open contacts are forcibly disconnected almost simultaneously.

The abovedescribed safety switch and actuator A and G is installed by mounting the safety switch A at any convenient position of the machinery guard and the actuator G to an opening edge of the guard door or gate aligned with the appropriate entry 42 or 43.