Actuator

Description

[0001] The present invention relates to an actuator for operation by fluid pressure.

[0002] U.K. Patent Specification No. 1401963 describes and claims an actuator including a cylinder, a piston and a piston rod movable relative to one another axially of the cylinder and interconnected by a mechanical linkage within the cylinder, the linkage including a rigid member pivoted to the piston rod at a first pivot, a first link pivoted at one end to the member at a second pivot and at its other end to the piston, a second link pivoted at one end to the cylinder and being, at its other end, pivoted to or pivotally engageable with the member at a third pivot, the second link being so arranged that the third pivot is always nearer the piston than the pivotal connection between the second link and the cylinder, and the mechanical linkage being so arranged that the second and third pivots can be: (a) on opposite sides of the axis of the piston or; (b) on the same side of the axis of the piston but with the second pivot nearer to the axis than the third pivot.

[0003] It is the object of this invention to provide an actuator that is of stronger construction in which the engagement to form the third pivot is more reliable and which can be made suitable for a relatively long working stroke.

[0004] According to the invention there is provided an actuator comprising a cylinder within which are a piston, a piston rod and a mechanical linkage arranged to transmit axial movement of the piston to the piston rod at a velocity ratio that decreases as the piston nears the end of its travel towards the piston rod, the linkage including a rigid member pivoted to the piston rod at a first pivot, a link pivoted at one end to the rigid member at a second pivot and pivoted at its other end to the piston, a pin supported in the cylinder at an axial position intermediate the piston and the piston rod end of the cylinder and pivoted to or pivotally engageable with the rigid member to define a third pivot, the arrangement being such that when the piston is at the far end of its travel from the piston rod the second and third pivots are both on one side of the longitudinal axis of the piston rod, the rigid third pivot more offset to said one side of said longitudinal axis than the second pivot and as the piston moves towards the piston rod the second pivot moves to the other side of the longitudinal axis of said piston rod, characterised in that the pin is supported for transverse sliding movement along a line normal to the longitudinal axis of the piston rod, therigid member is an arm extending radially from a disc rotatably mounted at the first pivot in a bearing formed in the end of the piston rod, the disc defines an eccentrically positioned aperture which pivotally engages or is pivotally engageable with the pin at the third pivot.

[0005] In a preferred construction the pin is releaseably engageable with the disc, the end of the piston rod in which the disc is rotatably mounted moving axially towards or away from the pin as the piston moves and the pin entering into engagement with the disc as the disc approaches the pin.

[0006] Other features of the invention will be apparent from the accompanying drawings which illustrate, by way of example only, an embodiment of the invention and in which:

Figure 1 is a sectional side elevation of an actuator showing the piston at the top of its stroke;

Figure 2 is a sectional side elevation similar to Figure 1, but showing the piston at the bottom of its stroke;

Figure 3 is a sectional end elevation of part of the actuator with the piston at the top of its stroke the section being taken along lines A-B and C-D of Figure 1; and

Figure 4 is a detail side elevation showing the pin supported in a slideway in a lower end block.

[0007] The actuator shown in the drawings employs a toggle mechanism arranged to vary the force amplification throughout the stroke so that near the end of the working stroke when the piston nears the bottom of the cylinder the force amplification is large, whereas during the first part of the working stroke the force amplification is small or even negative. Such an actuator has application to, for example, a punch in which the upper part of the stroke is required only for the purpose of giving clearance to a workpiece to be inserted in and removed from the dies.

[0008] Referring now to Figures 1 and 2, a piston 1 is slidable in a cylinder 2 having a lower end block 3 slidably supporting a piston rod 7. The upper end 8 of the piston rod is flattened and of less thickness than the rod diameter. It includes a bearing whose pivot axis is slightly offset to one side of the axis of the piston rod and a downwardly directed nose 9 on said one side bounding a slot in a lower portion of said bearing. The presence of the offset enables the actuator to give increased power and provide some compensation for side loads on the bearing. The tip of the nose is bevelled to provide a lead-in 10 and its inner face forms a slideway 11 for guiding a pin 23 through the slot in the bearing. A disc 14 pivots in the bearing and has a recess 15 opening to its ege. Overlying the disc 14 and secured to either side thereof are link plates 16 and 16a also formed with recesses corresponding to part of the slideway 11 and recess 1 5. The ends of the link plates 16 and 16a remote from the recesses are provided with pivot holes. One end of a link member 17 is pivoted to the link plates by means of a pivot pin 18 and the other end thereof is pivoted to the piston 1 by means of a pivot pin 19.

[0009] The lower end block 3 has a vertical slot terminating in a vertical end wall 20 and bounded by side walls 21 and 22. The piston rod 7 and link plates 16 and 16a can move axially in the slot, planar surfaces 28 on the link plates sliding over the upper portion of end wall 20 when the piston is towards the top of its stroke. Formed in side walls 21 and 22 adjacent end wall 20 at an axial position appropriately spaced from the base of the end block 3 are transversely extending slideways which slidably support the pin 23 mounted at its ends on respective trunnion blocks 24 and 25. Figure 4 shows the trunnion block 24 in its slideway 26, the pin 23 being retained by means of circlip 27.

[0010] As the piston 1 moves down the cylinder the nose 9 approaches the pin 23 which is initially at the left hand end of the slideway as seen in Figure 1. As the piston descends further the pin 23 moves along the guide surface 11 and into the bearing until it is received within the recess 15. Further downward movement of the piston causes the disc 14 and link plates 16 and 16a to rotate to the position shown in Figure 2, the pin 23 being trapped within the bearing and being carried around the inner surface thereof. During the downward stroke the pin 23 moves to the right as seen in Figure 1, the movement being denoted by an arrow. Since the pin is free to move transversely but not axially, the net effect is that the piston rod moves very much more slowly during the latter part of its stroke and a large amplification of force is obtained. When the piston moves upwardly the toggle mechanism reverses and the pin 23 disengages with the bearing, its movement being denoted by the arrow in Figure 2.

[0011] Various modifications may, of course, be made to the embodiment described herein without departing from the invention. For example, movement of the pin 23 need not be strictly at right angles to the axis of the piston. If the slideway 26 is inclined upwards at an angle to the axis of the piston 1, there is a counteracting movement between the piston and the pin which may be advantageous in some applications. In another possible modification, the actuator may be caused to lock at the end of the working stroke either by means of an over- centre action or by mechanical action. When the line between the centre of the pin 23 and the centre of the bearing moves across a plane parallel to the piston axis, the piston rod is, of course, locked by an over-centre action. It has, however, been found with reference to the present actuator that, provided that the angle between said line and said plane is less than approximately 10 degrees, friction will lock the piston rod notwithstanding that an overcentre action does not quite take place.

[0012] In the apparatus described above the releaseable pin 23 engages with the bearing more reliably than the apparatus shown in Figure 2 of British Patent Specification No. 1,401,963 and because of the release feature the present apparatus is not limited to a relatively short working stroke as in the apparatus shown in Figure 3 of the said specification. If, however, only a relatively short working stroke is required the slotted construction of the top of the piston rod may be replaced by a continuous eye with appropriate modification to the shape of the link plates.

[0013] While the actuator described herein is primarily intended for pneumatic use, it will be appreciated that the invention also has application to hydraulic actuators, particularly those intended for use at comparatively low hydraulic pressures.

Claims

1. An actuator comprising a cylinder (2) within which are a piston (1), a piston rod (7) and a mechanical linkage (16, 16a, 17) arranged to transmit axial movement of the piston (1) to the piston rod (7) at a velocity ratio that decreases as the piston (1) nears the end of its travel towards the piston rod (7), the linkage including a rigid member (16, 16a) pivoted to the piston rod (7) at a first pivot (14), a link (17) pivoted at one end to the rigid member (16, 16a) at a second pivot (18) and pivoted at its other end to the piston (1), a pin (23) supported in the cylinder at an axial position intermediate the piston (1) and the piston rod end of the cylinder (2) and pivoted to or pivotally engageable with the rigid member (16, 16a) to define a third pivot, the arrangement being such that when the piston (1) is at the far end of its travel from the piston rod (7) the second and third pivots (18, 23) are both on one side of the longitudinal axis of the piston rod (7) with the third pivot (23) more offset to said one side of said longitudinal axis than the second pivot (18) and as the piston (1) moves towards the piston rod (7) the second pivot (18) moves to the other side of the longitudinal axis of said piston rod (7) characterised in that the pin (23) is supported for transverse sliding movement along a line normal to the longitudinal axis of the piston rod (7), the rigid member (16, 16a) is an arm extending radially from a disc (14) rotatably mounted at the first pivot in a bearing formed in the end (8) of the piston rod (7), the disc defines an eccentrically positioned aperture (15) which pivotally engages or is pivotally engageable with the pin (23) at the third pivot.

2. An actuator according to Claim 1 wherein the pin (23) is releaseably engageable with the disc (14), the end (8) of the piston rod (7) in which the disc (14) is rotatably mounted moving axially towards or away from the pin (23) as the piston (1) moves and the pin entering into engagement with the disc (14) as the disc (14) approaches the pin (23).

Revendications

1. Actionneur comprenant un cylindre (2) dans lequel se trouve un piston (1), une tige de piston (7) et une liaison mécanique (16, 16a, 17) propre à transmettre le déplacement axial du piston (1) à la tige de piston (7) à un rapport de vitesse qui décroît à mesure que le piston (1 ) se rapproche de l'extrémité de sa course vers la tige de piston (7), la liaison mécanique comprenant un organe rigide (16, 16a) articulé à la tige de piston (7) par un premier pivot (14), une biellette (17) articulée à une extrémité à l'organe rigide (16, 16a) par un deuxième pivot (18) et à son autre extrémité au piston (1), une broche (23) montée dans le cylindre à un endroit axial situé entre le piston (1) et l'extrémité côté tige de piston du cylindre (2) et articulée à l'organe rigide (16, 16a) ou pouvant être engagée à pivotement avec cet organe pour former un troisième pivot, l'agencement étant tel que, lorsque le piston (1) se trouve à l'extrémité éloignée de sa course par rapport à la tige de piston (7), le deuxième et le troisième pivot (18, 23) se trouvent tous deux d'un côté de l'axe longitudinal de la tige de piston (7), le troisième pivot (23) étant davantage décalé vers ce premier côté de l'axe longitudinal que le deuxième pivot (18) et, à mesure que le piston (1) se rapproche de la tige de piston (7), le deuxième pivot (18) se déplace de l'autre côté de l'axe longitudinal de la tige de piston (7), caractérisé en ce que la broche (23) est montée de manière à coulisser transversalement suivant une ligne perpendiculaire à l'axe longitudinal de la tige de piston (7), l'organe rigide (16, 16a) est un bras qui s'étend radialement à partir d'un disque (14) monté à rotation par le premier pivot dans un palier formé dans l'extrémité (8) de la tige de piston (7) et le disque définit une ouverture excentrique (15) qui engage à pivotement la broche (23) au niveau du troisième pivot ou peut être engagée à pivotement par celle-ci.

2. Actionneur suivant la revendication 1, dans lequel la broche (23) peut être engagée de manière amovible avec le disque (14), l'extrémité (8) de la tige de piston (7) dans laquelle le disque (14) est monté à rotation se déplaçant axialement vers la broche (23) ou depuis celle-ci à mesure que le piston (1 ) se déplace et la broche s'engageant dans le disque (14) lorsque ce disque (14) se rapproche de la broche (23).

Ansprüche

1. Betätigungsorgan mit einem Zylinder (2), darin angeordnetem Kolben (1), Kolbenstange (7) und einem mechanischen Lenkergestänge (16, 16a, 17) zur Übertragung der axialen Bewegung des Kolbens (1) auf die Kolbenstange (7) mit einem Geschwindigkeitsverhältnis, das bei Annäherung des Kolbens (1) gegen Ende seines zur Kolbenstange (7) gerichteten Hubes abnimmt, wobei das Lenkergestänge ein starres Glied (16, 16a) aufweist, das an der Kolbenstange (7) an einem ersten Gelenk (14) angelenkt ist, ein Lenker (17) an einem Ende mit dem starren Glied (16, 16a) an einem zweiten Gelenk (18) und an seinem anderen Ende mit dem Kolben (1) gelenkig verbunden ist, und ein vom Zylinder an einer axialen Stelle zwischen dem Kolben (1) und dem Kolbenstangenende des Zylinders (2) getragener Stift (23) mit dem statten Glied (16, 16a) unter Bildung eines dritten Gelenkes gelenkig verbunden oder gelenkig verbindbar ist, wobei die Anordnung derart ist, daß, wenn der Kolben (1) an seinem von der Kolbenstange (7) fernen Ende seines Hubes ist und die zweiten und dritten Gelenke (18, 23) sich beide auf einer Seite der Längsachse der Kolbenstange (7) befinden und das dritte Gelenk (23) mehr seitlich zu dieser Längsachse versetzt ist als das zweite Gelenk (18) und wenn der Kolben (1) sich in Richtung der Kolbenstange (7) bewegt, das zweite Gelenk (18) sich zur anderen Seite der Längsachse der Kolbenstange (7) bewegt, dadurch gekennzeichnet, daß der Stift (23) quergleitbar längs einer Senkrechten zur Längsachse der Kolbenstange (7) abgestützt ist, das starre Glied (16, 16a) als Arm ausgebildet ist, der sich radial von einer Scheibe (14) erstreckt, welche drehbar an dem ersten Gelenk in einem Lager befestigt ist, das im Ende (8) der Kolbenstange (7) ausgebildet ist, wobei die Scheibe eine exzentrisch gelagerte Öffnung (15) definiert, welche gelenkig mit dem Stift (23) an dem dritten Gelenk in Eingriff bzw. in Eingriff bringbar ist.

2. Betätigungsorgan nach Anspruch 1, dadurch gekennzeichnet, daß der Stift (23) lösbar in Eingriff mit der Scheibe (14) bringbar ist und das Ende (8) der Kolbenstange (7), in dem die Scheibe (14) drehbar befestigt ist, sich axial zum Stift (23) hin oder von diesem weg bewegt, wenn der Kolben (1) sich bewegt und der Stift in Eingriff mit der Scheibe (14) bei deren Annaherung an den Stift (23) kommt.

Drawing