GB2168447A - Toggle-linkage for platen press - Google Patents

Abstract

A platen mechanism is suitable for use with an electrical interface having a very large number of spring contacts, which requires the application of a large force in a controlled manner. A jack 13 is freely supported by the pivot points 2 of toggle linkages 34 which couple a movable platen 5 member to a stationary one 6. The linkages are also coupled together by levers 20, 23 to ensure that the orientation of the plane of the movable member remains constant as it moves. <IMAGE>

Description

SPECIFICATION Platen mechanism This invention relates to a platen mechanism in which a plate is to be moved against a force from a first position to a second position whilst maintaining orientation substantially constant. The invention is particularly suitable for use with an electrical interface arranged to facilitate the testing of printed circuit boards in which an array of a very large number of spring loaded probes associated with the electrical interface are brought into contact with the circuit under test. The force required to compress the springs can be very high in view of the large number of probes involved, but it is important to bring the probes into contact in a controlled manner without skewing either the printed circuit board or a platen which carries the array of probes.

The invention seeks to provide a platen mechanism which is very robust and which is of a simple and economical construction.

According to this invention a platen mechanism comprises an actuator having two portions which are movable relative to each other when the actuator is energised; each portion being connected to a respective pivotted linkage which is coupled to a platen member and a reaction member and which acts to move the platen member with respect to a reference plane; and a coupling linkage connected so as to hold the plane of the platen member parallel to said reference plane during movement of the platen member.

Preferably the actuator comprises a pneumatic or hydraulic jack in which a piston is caused to move within a housing by virtue of a fluid pressure difference acting on the opposite sides of the piston.

Typically the hydraulic jack may be operated by the application of compressed air or a partial vacuum to one side or other of the movable piston.

Typically, a shaft is connected to a piston which is slideable within the housing with the housing itself and the shaft constituting the two movable portions of the actuator. In this way the actuator operates on the pivotted linkages themselves and not directly on the movable platen member, so that when the actuator is energised it moves with the pivotted linkages. Thus in the case of the pneumatic /hydraulic jack its housing and pistons both move in opposite directions and the movement will preferably be by equal amounts. Preferably again, the actuator is wholely supported by its couplings with the respective pivotted linkages.

Preferably each of said pivotted linkages has four attachment points, two of which are mounted on the platen member and two of which are mounted on a reaction member.

Conveniently the resulting four attachment points on each of the platen member and on the reaction member are spaced so as to distribute as widely as possible the forces acting upon them.

It is much preferred that the pivotted linkages are such that at its furthest distance from its initial rest position the platen member is held in a stable position; that is to say it remains in that position even if the pneumatic /hydraulic jack relaxes. In this case, in order to withdraw the platen member to its rest position it is necessary to provide positive acting means to achieve this and it is therefore convenient to use a double action pneumatic/hydraulic jack for this purpose. In such a jack the piston can be moved in a positive manner in both directions.

Conveniently, the coupling linkage utilises part of said pivotted linkage in order to keep the plane of the platen member parallel to the reference plane as it moves. As the lateral position of the platen member will generally be of importance, it is preferered to provide means for preventing undesired transverse movement. Such means can conveniently take the form of a slide arrangement in which an elongate slider is free to move within a support without experiencing lateral movement.

Additionally, some coupling linkage is very desirable to ensure that the lateral action of the jack is equalised about the centre.

The invention is further described by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a sectional view of a platen mechanism, and Figures 2, 3, 4 and 5 show alternative details of a coupling linkage.

Referring to Fig. 1, a trunnion mounted double acting hydraulic jack 1 is freely supported by trunnion pivots 2 forming part of pivotted linkages 3 and 4 which couple a movable platen member 5 to a reaction member 6, which forms part of a rigid housing 7 having a reaction plate 8 adjacent to the platen member 5.

A pneumatic jack could be used in place of the hydraulic jack. In practice two sets of linkages 3 are provided both of which are mounted on a common shaft passing through the trunnion pivot 2, the two sets being on opposite sides of the jack axes. Each of the pivotted linkages 3 is attached to the platen member and the reaction member by attachment points 9 and 10 respectively. Similarly two sets of pivotted linkages 4 are provided with them being attached to the platen member and the reaction member by attachment points 11 and 12 respectively. In the drawings, only one set of each of the linkages 3 and 4 is visible; each consists of a pair of short arms 33, 34.

The hydraulic jack 1 comprises a cylinder 13 within which a piston is mounted, the piston being attached to a shaft 14, the end of which is pivotally mounted to the trunnion pi vot 2.

In the rest position the platen member 5 is in its lowest position relative to plate 8 and jack 1-this is as illustrated in Fig. 1, and the upper surface of the platen member defines a reference plane in this position. When the jack 1 is actuated, the shaft 14 is forced in the direction of the arrow 15 causing an equal and opposite movement of the housing 13 in the direction of the arrow 16. The resulting movement of the pivots 2 cause the platen member 5 to move in an an upwards direction towards the reaction plate 8. At the full extent of the movement, the two arms 33, 34 forming part of each linkage 3, 4 are aligned or possibly passed to a slightly over-centre position so that the platen member 5 remains in a stable position, even if the hydraulic jack is relaxed.In order to ensure that the platen member 5 moves in a vertical direction without lateral transverse movement two slider arrangements are provided. These consist of guides 19 which are slideable within a support 20 in a manner which prevents lateral movement.

Fig. 2 shows a portion of the platen mechanism in more detail. In particular, it illustrates a coupling linkage which is attached to the pivotted linkages 3 and 4 so as to ensure that the platen member 5 is at all times held parallel to its reference position, which is in fact, parallel to the reaction plate 8.

For clarity of illustration the jack is omitted from this drawing. The coupling linkage consists of three members 20, 21 and 23. The member 21 is a short lever which is pivotted at its centre point to an upstanding portion of the reaction housing 7. Each end of this arm 21 is pivotally mounted to a longer arm, 20, 23, the other ends of which are attached to the pivots 2. The action of this linkage is to ensure that the pivotted linkages 3 and 4 always move by the same amount. Such a coupling linkage is clearly operative only for a relatively small degree of movement. Alternative coupling linkages which do not suffer from this disadvantage are shown in Figs. 4 and 5. However, as indicated, for normal movements which are small, the coupling linkage illustrated in Fig. 2 is quite satisfactory.

Fig. 3 shows a further form of compensating coupling linkage, in which compensating links 25 and 26 are integral with one half of the original short arms forming part of the pivotted linkages 3 and 4. At their inner ends the compensating links 25 and 26 are joined by a short linking bar 27 which ensures that all links move together. Alternative and more precise methods of joining the compensating links 25 and 26 are illustrated in Figs. 4 and 5. In Fig. 4, the two links are provided with meshing teeth 28 to ensure that both links 25 and 26 always experience exactly the same angular movement. In Fig. 5 flexible bands 28 and 29 are provided to achieve the same purpose.

Although in the drawing only a single set of coupling linkages is illustrated, in practice, two such sets would preferably be provided, one on either side of the jack 1. The configurations illustrated permit just a single actuator in the form of a jack to apply distributed force to four separate points which can be located towards the corners of a rectangular movable platen member. However, if desired, additional hydraulic jacks could be provided. Coordination of additional units will be achieved by linking rods through the pivot points 10 and 12, the rods being keyed to arms 34. It will be noted that configuration of the pivotted linkages 3 and 4 ensures that the maximum force exerted by the jack occurs towards the end of the stroke at the point where in all probability it will be needed most. Furthermore, failure of the jack in either of its two end positions enables the current position of the platen member to be retained in a stable manner.

Claims (11)

1. A platen mechanism including an actuator having two portions which are movable relative to each other when the actuator is energised; each portion being connected to a respective pivotted linkage which is coupled to a platen member and a reaction member and which acts to move the platen member with respect to a reference plane; and a coupling linkage connected so as to hold the plane of the platen member parallel to said reference plane during movement of the platen member.

2. A mechanism as claimed in claim 1 and wherein the actuator comprises a pneumatic or hydraulic jack.

3. A mechanism as claimed in claim 1 or 2, and wherein the actuator is wholly supported by the pivotted linkage to which it is connected.

4. A mechanism as claimed in claim 1, 2 or 3 and wherein each of said pivotted linkages has four attachment points, two of which are mounted on the platen member and two of which are mounted on a reaction member.

5. A mechanism as claimed in claim 4 and wherein the four attachment points on each of the platen member and on the reaction mem ber are spaced apart so as to distribute as widely as possible the forces acting upon them.

6. A mechanism as claimed in any of the preceding claims and wherein the pivotted linkages are such that at its furthest distance from its initial rest position the platen member is held in a stable position.

7. A mechanism as claimed in claim 6 and wherein the jack is provided with a double action to return the platen member to its initial rest position.

8. A mechanism as claimed in any of the preceding claims and wherein said pivotted linkages form part of said coupling linkage.

9. A mechanism as claimed in any of the preceding claims, and wherein means are provided for preventing transverse movement of the platen member as it moves towards and away from said reference plane.

10. A mechanism as claimed in any of the preceding claims, and wherein a plurality of actuators are provided, and which are linked together so as to operate in unison.

11. A mechanism substantially as illustrated in and described with reference to Fig.

1, and Figs. 2, 3, 4 or 5 of the accompanying drawing.