GB2178690A

GB2178690A - A gripping device

Info

Publication number: GB2178690A
Application number: GB08600962A
Authority: GB
Inventors: Iii William Williamso Montalvo
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-08-05
Filing date: 1986-01-16
Publication date: 1987-02-18
Also published as: IT1191870B; DE3543465A1; IT8647818A0; AU5112285A; FR2585608A1; NL8600548A; GB8600962D0; JPH0562646B2; JPS62171507A

Abstract

A gripping device (1) comprises a spring (2), means (3-5) for changing the length of the spring and a link (8) connected to the length changing means (3-5) such that movement of said length changing means causes movement of the link causing a first jaw (24) connected to the link to move towards, or away from, a second jaw (25) so as to grip or to release an object. <IMAGE>

Description

SPECIFICATION A gripping device The present invention relates to a gripping device particularly for contacting an object with a constant force. The contacting may be for the purpose of gripping the object or for moving the object.

United States Patent No. 4,457,408 describes a friction coupling mechanism for disc-type brakes comprising a spring-actuated piston and cylinder module and a cam actuated caliper assembly. The caliper assembly variably multiplies the module's actuating force by means of circular cam segments and coordinated cam follower members in cooperating relationship therewith. As the actuating spring force decreases linearly with spring extension, the tangent angle of incidence between the arcuate surfaces of the cam segments and the respective cooperating surfaces of the cam followers also change linearly, but inversely to decaying spring pressure, to insure application of a constant normal braking force at the disc, regardless of the spring extension within spring limits.

The present invention seeks to provide an improved gripping device for engaging objects or bodies with a fixed force within a predetermined size range, using a decaying spring force converted to a constant force within the device. The device has an inherent capacity for multiplication of spring force. The term "gripping" is also to be understood as including clamping, holding, actuating or moving objects or bodies in this manner.

According to the invention, there is provided a gripping device comprising a resilient biasing means; means for changing the length of said resilient biasing means; link means having a longitudinal axis and being connected to said length changing means, such that movement of said length changing means causes movement of said link means, whereby said longitudinal axis moves through an angle 6; and a first jaw means capable of movement either towards, or away from, a second jaw means whenever said longitudinal axis moves through said angle 8, so as to grip or release an object.

The device of the present invention takes the linearly decreasing force of a spring of the "Hookes" type and, as extension of the spring occurs, the changing angle of the linkage functionally multiples the decaying force of the spring in such a way as to yield a constant resultant force within certain limits.

The device has two principal embodiments, a single link device and a dual link device. The difference between the two is that the resultant forces in the two or dual link system are half of those in a single link system, all dimensions of link, load, and angle being held the same.

The primary description is for the two or dual link system, because of its complexity; but the relationship of the description to the single link system will be readily apparent.

A linkage assembly variably multiplies the device's actuating force by means of a bar force arm and attached movable bar in cooperating relationship therewith. As actuating spring force decreases linearly with spring extension, the tangent of the angle of variation between the bar force arm and the movable bar also changes linearly but inversely to decaying spring pressure, to insure application of a constant force between the gripping jaws regardless of the spring extension within the spring limits.

The present invention has the advantages that the force applied by the jaws to an object remains constant even when the gripping means move through greater or less distances to accommodate the size of smaller or larger objects to be held.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of the gripping device of the present invention having a dual link means, Figure 2 shows diagrammatically the variable relationship between the spring input force and the resultant gripping force, Figure 3 shows a front view of the gripping device of Fig. 1, Figure 4 shows a section view of the gripping device taken along the line 4-4 of Fig. 3, Figure 5 shows a rear view of the gripping device of Fig. 1 with the spring extended, Figure 6 shows a rear view of the gripping device of Fig. 1 with the spring compressed, Figure 7 shows a bottom section view of the gripping device taken along the line 7-7 of Fig.

5, been rotated through 1800, Figure 8 shows a bottom section view of the gripping device taken along the line 8-8 of Fig.

6, rotated through 1800, Figure 9 shows another embodiment of the gripping device of the present invention illustrating the device having the spring extended and compressed, Figure 10 shows a section view of the gripping device taken along the line 10-10 of Fig. 9, Figure 11 shows a section view of the gripping device taken along the line 11-11 of Fig. 9 with the spring extended, Figure 12 shows a section view of the gripping device taken along the line 12-12 of Fig. 9 with the spring compressed, Figure 13 shows a further embodiment of the gripping device of the present invention having a single link means, Figure 14 shows a bottom partial section view of the single link gripping device taken along the line 14-14 of Fig. 13, and, Figure 15 shows a bottom partial section view of the single link gripping device taken along the line 15-15 of Fig. 13.

For the purpose of the embodiments to be described hereinafter it is to be assumed that all parts shown herein are perfectly rigid with the exception of the spring.

Spaces are shown between some of the parts for the increased clarity, but it is to be assumed that all sliding and rotating parts fit perfectly, and remain in perfect alignment for the purpose shown or described, and that the operation of the system is totally friction free, except where the discussion implies obvious frictional contact.

Fig. 1 shows a perspective view of the gripping device 1 of the present invention. The gripping device 1 comprises a resilient biasing means, or spring means 2, as well as comprising a means for changing the length of resilient biasing means, which is a means for compressing the spring means. In all the drawings, like reference numerals are used throughout for the parts of the device.

The spring compressing means comprises a reaction plate 3 adjacent to one end of the spring means 2, which end will be called the top end of spring means 2. The spring fits within the cut out lower inner portion of plate 3. The spring compressing means also comprises a stop block 4 adjacent to the other end, or lower end, of the spring means. The compressing means further comprises a tie rod 5 extending between the reaction plate 3 and the stop block 4, with the tie rod being located within the hollow central portion of the spring means, as shown in Fig. 1.

The spring compressing means additionally comprises a first handle 6 attached to the reaction plate 3, and a second handle 7, attached to the stop block.

The resilient biasing means 2 is shown as a coil compression spring of the "Hookes" type having a force constant which is linear to respect to compression length. The constant is defined and expressed in terms of force per unit length of compression, e.g. kilogrammes/cm or pounds/per inch. However, any type of spring with a force per unit length relationship such as described above, will function within the gripping device of the present invention. Some further examples of suitable types of springs include the coil, leaf, disc, washer, air, or gas type of spring.

While the drawings illustrate the use of handles 6 and 7, it is to be mentioned that these handles are shown as one possible embodiment within the description. The present gripping device is intended to be not only a manually operated device. The gripping device 1 can be energized, or deenergized by any type of pressure delivering system, such as pneumatic, hydraulic, electric or otherwise.

For the second embodiment shown in Figs. 13 to 15, the same reference numerals are used for the same features which correspond to those features found in Figs. 1 to 12, except that in Figs. 13 to 15, the reference numerals have a prefix of "100".

The gripping device also comprises a link means, such as the bar force arm 8 which has a longitudinal axis 9 as shown in Fig. 3, and the link means is connected to the length changing means. Thus movement of the length changing means causes movement of the link means, whereby the longitudinal axis 9 moves through an angle 6 as shown in Fig. 3. As can be seem from Fig. 3, the angle theta 0 comprises the angle between the longitudinal axis 9 of the bar force arm, and the longitudinal axis 10 of a movable bar 11 for the first embodiment.

The same relationship exists between the longitudinal axes 109 and 110 which will produce the angle (then)6 for the second embodiment which can be seen also in Fig. 13.

As shown in Fig. 1, the dual link means comprises the bar force arm 8 which is connected by retaining means 12 and bar pin means 13 to the movable bar 11. Bar pin means 13 slides within slot 14 shown in Fig. 1 to be within the sleeve 15.

In the first embodiment shown in Fig. 1, the link means also comprises the sleeve force arm 16 which is connected through the retaining means 17 and the sleeve pin 18 to the sleeve means 15. In the second embodiment shown in Figs. 13 to 15 the single link means has no sleeve force arm.

The gripping device 1 further comprises a yoke 19 positioned around the first end 20 of the sleeve force arm 16. The yoke 19 is simultaneously positioned around the first end 21 of the bar force arm 8. A yoke pin means 22 connects the yoke 19 to the first end of each of the sleeve force arm and the bar force arm.

The tie rod 5 extends completely through the stop block 4 and is attached by one end thereof to the yoke 119. This can be seen in Fig. 1. This attachment may be for example by welding the tie rod to the yoke, or by screw thread and fastener means. The tie rod extends through the reaction plate 3 at the other end of the tie rod and a nut 23 is screwed onto the top end of the tie rod 5. It is also possible to place a washer, although not shown in Fig. 1, between the nut 23 and reaction plate 3.

The gripping device further includes a first jaw means, or bar jaw 24, which is capable of movement either towards or away from, a second jaw means or sleeve jaw means 25, whenever the longitudinal axis 9 of the bar force arm moves through the angle 6. This movement of the first jaw 24 toward the second jaw 25 enables the device to grip an object. The movement of the first jaw away from the second jaw would permit the device to release the object previously gripped. This applies to a situation in which the jaws 24 and 25 are to be brought into contact with the outside surfaces of an object to be gripped.

On the other hand, if the jaws 24 and 25 are to be brought into contact with the inside surfaces of, or to be placed within, an object to be gripped, the the following opposite relationship would exist. In order to grip the object, jaws 24 and 25 when placed within the object would be moved away from each other. Then in order to release the object, jaws 24 and 25 would be moved towards each other.

As shown in Fig. 1 the sleeve 15 has the second jaw 25 attached thereto, in such a manner that this second jaw 25 is stationary and immovable. Located within the sleeve 15 is the movable bar 11, and this movable bar has the first or movable jaw 24 attached thereto. The sleeve 15 has a longitudinal slot 26, as shown in Fig. 3, within which the first movable jaw is located for movement either towards, or away from the second or stationary jaw, so as to be able to grip or to release an object.

The longitudinal slot 26 is also shown in Figs. 5, 6, 7, 8, 11 and 12.

The sleeve force arm 16 has its second end 27 connected to the sleeve 15 by means of retaining means 17 and sleeve pin 18. The bar force arm 8 has its second end 28 connected to the movable bar 11 by means of retaining means 12 and bar pin 13.

A trunnion plate 29 is placed at one end thereof adjacent to the sleeve 15. In the embodiment as shown in Fig. 10, the trunnion plate 29 may be attached at this end to the sleeve 15 by the appropriate attachment means, such as dovetail anchor means 30. The other end of the trunnion plate is connected by a bolt means to the stop block 4. As shown in Figs. 1 and 4, this bolt includes a pin 31 which is held in place by at one end by nut 32, and includes screw fastener 33 at the other end that fits within stop block 4. The trunnion plate 29 is maintained in a spaced relationship from the stop block by means of a spacer 34. Pin 31 is a trunnion shank and fastener means 32 is a trunnion nut.

Thus, it can be seen that the tie rod 5, the yoke 19, the bar force arm 8 and the sleeve force arm 16, the sleeve 15, the trunnion plate 29, and the stop block 4 are all continuously interconnected, whereby reciprocating movement of tie rod 5 as the spring 2 is compressed or decompressed, causes at least one of these force arms to move through the angle so that the jaws 24 and 25 open and close.

Fig. 2 shows diagrammatically the variable relationship between the spring input force F and the resultant gripping force FR.

Fig. 2 provides a visual representation of the inventive concept in its simplest form. The springs are chosen in such a way that the total travel from full compression (which distance is of choice) to free the length is the same as the distance marked "A" in Fig. 2. The starting and ending points of spring travel do not have to be as above, since free length is only one way of doing this. Free length as an end limit of travel produces an extreme result which will be discussed below.

The basic angle is chosen by selecting the amount of multiplication to be applied to the initial force exerted by the spring at its maximum design compression. The cotangent of the basic angle 6 is the value of the multiplication: COSO Multiplier= =COT6 SINS 6=Basic angle 61=any angle between limits; 0+0 02S, > 0 Some examples of this are the following: COT 26.5 =2.005 COT 18.4"=3.006 COT 45.0"=1.000 COT 63.4 =0.5007 It should be apparent after observation that a basis angle approaching 90 will yield an infinitely small multiplier, which may be useful in some applications.

In terms of the lengths "A" and "B" of Fig. 2, B the multiplier=-=COT8 A In operation, as the spring is allowed to force the linkage L to travel in the direction of Fs from the compressed spring position to full extension, the spring force decreases in a linear manner with respect to the unit distance the spring end of the linkage has travelled.

As this linear decreases in force takes place, the cotangent function of the changing angle 6 increases in such a way that the product of the spring force (except at freelength) and the cotangent of the angle 6 at any given point (except at 0 ) maintains the resultant force, FR constant at the value established by the basis angle and the initial spring force at full design compression.

At full spring extension the spring force is zero so the resultant based upon this would be zero. At zero angle (0,=0) the cotangent is infinite and in mechanics, multiplication by infinity is impractical. The rules of mathematics also state that any number multiplied by zero equals zero.

For these reasons, this point or limit should be avoided in utilizing the device.

The limits used for spring compression and extension do not have to be full, allowable compression, or free length, nor is the device restricted to only one spring or type of spring.

These limits for these parameters are merely illustrative.

In summary, as the spring goes from full design compression to full design extension (design meaning for this system, not for the spring), and as the angle 6 coincidentally moves toward its minimum design limit, the cotangent of that angle 01 increases in such a predetermined way as to maintain the resultant force function constant at the value determined by initial positions previously discussed, except at the limits previously discussed.

The function is described this way: 6= basic angle 61=any angle between limits Fs=spring force at any point FR resultant force constant COSS FR= . Fs=Fs. COT61 SINS1 The device 1 is constructed from component parts which are conveniently made of hard strong, tough and durable materials, for example metals, such as steel or brass. Bar jaw means 24 may be attached to the bar 11 by a suitable metal-to-metal joining technique such as welding, brazing or soldering. Likewise, the sleeve jaw means 25 may be attached to the sleeve 15 by the same joining technique.

From Fig. 4 it can be seen that the yoke 19 is an inverted, U-shaped, flat top bracket. The yoke comprises an outside arm 35 which contacts the sleeve force arm 16 and is remotely positioned from the sleeve 15. The yoke also includes an inside arm 36 which is in contact with the bar force arm 8 and is adjacent to the sleeve 15. "Adjacent" in this context means that the arm 36 is in sliding contact with the sleeve 15, while "remote" means that the arm 35 is located away from the sleeve 15. Completing the yoke is a flat top portion 37 which is connected at a right angle to the top part of each of the outside arm 35 and the inside arm 36.

As can be seen in Figs. 1 and 4, the yoke pin 22 is a hinge placed in the bottom part of the yoke and simultaneously passes through the outside arm 35, the sleeve force arm 16, the bar force arm 8, and the inside arm 36, so as to connect the yoke to these force arms. The tie rod 5 is attached to the flat top portion 37 of the yoke, such as by a screw thread means 38.

Thus, as tie rod 5 reciprocates up and down, arms 8 and 16 move arcuately around yoke pin 22.

The bar force arm 8 has an L-shaped cross section, with the first end 21 of the bar force arm being of narrower cross section than the second end 28 of the bar force arm. This first end 21 is connected to the yoke by means of yoke pin 22. This can be seen from Figs. 7, 8, 11 and 12, as well as from Figs. 1 and 4. The second end 28 of the bar force arm 8 is of a wider cross section than the cross section of the first end 21, and the second end 28 is connected to the movable bar 11 by bar pin 13.

The sleeve force arm 16 also has a L-shaped cross section. The first end 20 of the sleeve force arm 16 is of a narrower cross section than the cross section of the second end 27 of the sleeve force arm. This first end 20 is connected to the yoke, also by means of yoke pin 22.

The second end 27 of the sleeve force arm 16 is of a wider cross section than that of the first end 20. This second end 27 is connected to the sleeve 15 by means of sleeve pin 18.

As can be seen from Figs. 7, 8, 11 and 12, the second end 27 of the sleeve force arm 16 is of wider cross section than is the second end 28 of the bar force arm 8. Hence, the first end 21 of the bar force arm 8 can be, and is, located nearer to the sleeve 15; and the first end 20 of the sleeve force arm 16 is located farther from the sleeve 15, than is the first end 21 of the bar force arm 8.

The invention illustrated in Figs. 1 to 15 is based upon a compression spring in which the functioning of the gripping device is related to compressing the spring means 2. However, in a further embodiment (not illustrated in the drawings) the gripping device is enabled to function by utilizing an extension, or pull type of spring of the "Hookes" type. A gripping device utilizing an extension spring would be based upon removing the compression spring 2 of Fig. 1, and installing an extension spring between stop block 4 and the top portion 37 of yoke 19 with the tie rod 5 being located within the hollow central portion of the spring means.

The device 1 can be utilized, as can be seen by reference to Figs. 7 and 8 for gripping the outside surface of an object. Alternatively, the device 1 can be utilized for gripping the inside surface of an object, as can be seen by reference to Figs. 11 and 12 of the drawings.

In regard to the first application, the gripping device 1 is activated by bringing the handles 6 and 7 closer to each other, as can be seen in Fig. 3. In Fig. 3, the initial relationship between the handles 6 and 7 is shown in the dash, or phantom, lines. When these handles are brought together, the spring 2 is compressed. Stop block 4 is prevented from moving because it is fixed by means 31 to the trunnion plate 29 and linear motion of stop block 4 is prevented.

The force exerted by the handle 6 through the reaction plate 3, which is fixed to the tie rod 5, then forces the tie rod to move in a direction toward the bottom of Fig. 3 as shown in the drawings. As tie rod 5 slides through the central portion of stop block 4, it causes yoke 19 to move in a generally linear motion in the downward direction toward the bottom of Fig. 3 as indicated in the drawings. This motion is slightly cuirved through an angle 0 as shown in the drawing.By means of the yoke pin hinge 22, the sleeve force arm and the bar force arm are caused to rotate through an angle 6, until the maximum extent is reached producing the basic angle 6. The pin means 18 holds the sleeve force arm 16 in place such that the downward movement of yoke 19 is translated into a longitudinal movement of bar force arm 8. This longitudinal movement of bar force arm 8 is shown in Fig. 3 is within the longitudinal slot 14.

The movement of pin 13, which connects the bar force arm 8 to the movable bar 11, within slot 14, causes the movable bar 11 to move to the right as indicated in Fig. 3. This movement by bar force arm 8 creates the angle 6 as shown in Fig. 3, which is the angle between the longitudinal axis of the movable bar 11 and the longitudinal axis of arm 8 after it has traversed the longitudinal distance within slot 14.

Fig. 7 shows the relationship between the movable jaw 24 which is attached to the movable rod 11, and the stationary jaw 25 which is attached to the immovable sleeve 15. Fig. 7 also shows the relationship between the sleeve 15 and the bar 11 when the spring is extended as shown by the phantom lines in Fig. 3.

When the spring is compressed to the extent shown in Fig. 3, the device 1 would have its component parts as shown in Fig. 8. In other words, when the spring is compressed, the yoke 19 is moved into the position shown in the solid line in Fig. 3. When this happens, the bar force arm 8 moves from the position shown in Fig. 7 to that shown in Fig. 8 which by means of bar pin 13 causes the bar pin to shift within longitudinal slot 14 from the position shown in Fig. 7. The bar pin 13 moves from its location at the far left in Fig. 7 to the right hand portion of channel 14 as shown in Fig. 8. This causes the movable bar 11 to move from its position at the far left of Fig. 7 to the right as shown in Fig. 8.This movement of bar 11 toward the right will cause movable jaw 24 to move to the right such that the distance between jaws 24 and 25 will be increased to the maximum distance between jaws 24 and 25 as shown in Fig. 8.

Once this maximum distance between jaws 24 and 25 has been established, then an object to be held or to be moved, which is shown in phantom lines in Fig. 8, can be placed between jaws 24 and 25.

As soon as the object is in position between jaws 24 and 25, the spring is allowed to decompress, or expand, from the compressed position shown in Fig. 3 towards but not reaching the dotted line, phantom line, position shown in Fig. 3. When this occurs, the yoke 19 will be pulled upward to the phantom line position by tie rod 5. When that occurs the angle 6 will decrease from its maximum value back towards, but not reaching, its zero value. The movement of the tie rod 5 upward will cause bar force arm 8 to move and will cause bar pin 13 to move to the left as shown in Fig. 7 from its position in Fig. 8. As bar pin 13 moves to the left, the movable bar 11 will move to the left. As movable bar 11 moves to the left, movable jaw 24 will move to the left, so as to diminish the distance between jaws 24 and 25.Eventually jaw 24 will contact the object and press it against jaw 25, such that jaws 24 and 25 will firmly grip the outside surface of this object.

The force exerted between jaws 24 and 25 as they contact the object is created as follows.

In operation, as the spring 2 is allowed to force the linkage to travel in the direction from the compressed spring position in Fig. 8 towards full extension, in Fig. 7, the spring force Fs decreases in a linear manner with respect to the unit distance the spring has travelled.

As this linear decrease in force takes place, the cotangent function of the changing angle 6 increases in such a way that the product of the spring force Fs and the cotangent of the angle 01 at any given point maintains the resultant force, FR constant at the value established by the basis angle and the initial spring force, at full compression (Fig. 8).

During gripping a full spring extension is prevented so that the spring force is greater than zero and so the resultant based upon this is FR.

The requirement for utilizing this embodiment of the invention is that the outside diameter of the object must be greater than the minimum distance between the contact surfaces 24c and 25c of jaws 24 and 25 shown in Fig. 7. Clearly, if the object were of an outside dimension less than the minimum distance between jaws 24 and 25 shown in Fig. 7, jaws 24 and 25 would be unable to grip the object. Furthermore, the outside dimension of the object must be less than the maximum distance between the contact surfaces 24c and 25c of jaws 24 and 25 as shown in Fig. 8.

From a comparison of Figs. 7 and 8, it can be seen that the longitudinal slot 14 within which the bar pin 13 reciprocates, is at one end of sleeve 15. The longitudinal slot 26 in which the movable jaw 24 reciprocates is at the opposite end of sleeve 15. Thus, longitudinal slot 14 is at the opposite end of the sleeve 15 from the longitudinal slot 26.

Figs. 11 and 12 illustrate a second application of the device, in which the device 1 is used for gripping the inside surface of an object. In this construction of the device, the channel 14 within which the bar pin 13 reciprocates is located at the same end of the sleeve 15 in which channel 26 is located. Movable jaw 24 is placed within, and reciprocates within, longitudinal channel 26.

The device illustrated in Figs. 11 and 12 can be utilized for gripping an object along the inside surfaces of the object. The embodiment of the invention shown in Figs. 11 and 12 is based upon Fig. 9.

Fig. 1 shows the resultant tie rod angle 0 which is inherent in this particular configuration of the device 1.

As shown in Fig. 9 for the dual link embodiment, the distance between the centre of the bar 11 and the centre of the pin 31 is kept sufficiently high with respect to the force arm length such that the cosine of angle 0 will be sufficiently close to a value of 1.000 that the resultant loss will be neglible.

If the stop block 4 is fixed to the trunnion plate 29 (as it is in the dual link and the single link embodiments as 104 and 129) so rotation cannot occur, and the sliding dovetail feature 30 is used as shown in Fig. 10, it is possible to eliminate this angular motion completely, replacing it with traverse motion. Hence, the losses which accompany the anglular motion are eliminated.

It can be easily seen that these losses do not exist in the single link embodiment of the device 101 shown in Fig. 13.

When the handles of the device shown in Fig. 9 are located in the phantom position, the spring 2 is fully expanded such that, as can be seen from Fig. 11, the jaws 24 and 25 are spaced apart from the maximum distance.

From Fig. 9 it can be seen that when the handles are pressed towards one another, the spring 2 is compressed which causes yoke 19 to assume the solid line position shown in Fig. 9, and this causes jaws 24 and 25 to be located close to each other as shown in Fig. 12.

When the spring 2 of Fig. 9 is compressed and yoke 19 moves towards the lower part of Fig. 9, this causes bar force arm 8 to move to the right and causes bar pin 13 to move to the right in channel 14 as indicated by the arrow in Fig. 12. The movement of bar pin 13 to the right causes the movable bar 11 to move to the right, such that movable jaw 24 connected thereto also moves to the right within the longitudinal channel 26. Thus, movable jaw 24 and stationary jaw 25 are positioned as closely together as possible in Fig. 12, such that the distance between jaws 24 and 25 is at a minimum. In Fig. 11 jaws 24 and 25 are spaced apart at the maximum distance.

As shown in Fig. 12 after jaws 24 and 25 move together such that they are spaced apart by the minimum distance, it is possible for jaws 24 and 25 to be placed within an object to be held. After being placed within the object to be held, the handles are moved apart such that spring 2 is expanded towards but not reaching the phantom line location shown in Fig. 9. This causes bar force arm 8 to move back toward the left as shown in Fig. 11. Movement of bar force arm 8 to the left causes bar pin 13 to move toward the left, which pulls movable bar 11 back towards the left, as indicated by the arrow.

As movable bar 11 moves towards the left, movable jaw 24 is pulled toward the left, such that eventually jaws 24 and 25 are pressed firmly against inside surfaces of the object to be held.

The requirements for the dimensions of the object to be held along its inside surfaces are such that the inside diameter of the object must be less than the maximum distance between the contact surfaces 24c and 25c of jaws 24 and 25 as shown in Fig. 11, but must be greater than the minimum distance between the contact surfaces 24c and 25c of jaws 24 and 25 as shown in Fig. 12.

In Figs. 7 and 8, the contact surfaces 24c and 25c are adjacent interior jaw surfaces for contacting the exterior surface of the object. In Figs. 11 and 12, the contact surfaces 24c and 25c are remote exterior jaw surfaces for contacting the interior surface of the object.

In operation, as the spring 2 is allowed to force the linkage to travel in the direction from the compressed spring position in Fig. 12 to full extension, in Fig. 11, the spring force decreases in a linear manner with respect to the unit distance the spring has travelled.

As this linear decrease in force takes place, the cotangent function of the changing angle 6 increases in such a way that the product of the spring force Fs and the cotangent of the angle 6i at any given point maintains the resultant force, FR constant at the value established by the basis angle and the initial spring force at full compression of Fig. 12.

During gripping a full spring extension is prevented so that the spring force is greater than zero so the resultant based upon this is FR.

The embodiment of the device 101 shown in Figs. 13, 14 and 15 has the single link, or single bar force arm 108, instead of having the dual link features of the device 1 as shown in Figs. 1 to 12. For the sake of brevity, the features of device 101 and the mode of operation of the device 101 which are the same as that for device 1, will not be repeated.

The embodiment of the device 101 shown in Fig. 14 is analogous to that shown in Figs. 7 and 8 for device 1. This can be seen by the fact that for device 101 the longitudinal channels 114 and 126 are at the opposite ends of the sleeve 115, just as for device 1 in Figs. 7 and 8, the longitudinal channels 14 and 26 are at the opposite ends of sleeve 15. Thus, the embodiment of device 101 shown in Fig. 14 would be utilized analogously to the device shown in Figs.

7 and 8 such that jaws 124 and 125 will grip the outside surfaces of an object.

The embodiment of the device 101 shown in Fig. 15 is analogous to that shown in Figs. 11 and 12 for device 1. This can be seen by the fact that for device 101 the longitudinal channels 114 and 126 are at the same end of the sleeve 115, just as for device 1 in Figs. 11 and 12, the longitudinal channels 14 and 26 are at the same end of sleeve 15. Thus, the embodiment of device 101 shown in Fig. 15 would be utilized analogously to the device shown in Figs. 11 and 12, such that jaws 124 and 125 will grip the inside surfaces of an object.

Jaws 24 and 25, as well as jaws 124 and 125, need not necessarily be coplanar. Preferably these jaws are coplanar, as is shown in the drawings. The advantage of having these jaws copolanar is that the normal force applied between the jaws and against the surface of the object to be held is thereby coplanar. This will prevent the creation of a torque or twisting force, or any possible bending force, applied against the surfaces.

However, if the configuration of the object to be contacted is of a unique shape, then it may be possible to have the grippng jaws not aligned in a coplanar manner, if a stable holding pattern between the jaws and the object can still be maintained.

The device according to the present invention can be used as one of the following, or can be used in combination with one of the following: brakes and clutches, pliers, tongs, forceps or haemostatic devices, robotic gripping devices, food handling devices, devices for constant force motion of the two objects with respect to each other, clamp devices, holding devices for anything in which controlled force is desired or required, and suspension devices.

Claims

1. A gripping device comprising a resilient biasing means; means for changing the length of said resilient biasing means; link means having a longitudinal axis and being connected to said length changing means, such that movement of said length changing means causes movement of said link means, whereby said longitudinal axis moves through an angle 6; and a first jaw means capable of movement either towards, or away from, a second jaw means whenever said longitudinal axis moves through said angle 6, so as to grip or to release an object.

2. A gripping device according to Claim 1, wherein said resilient biasing means is a spring means said length changing means is a means for compressing said spring means, and said link means comprises at least one force arm.

3. A gripping device according to Claim 2, wherein said spring compressing means comprises a reaction plate adjacent to one end of said spring means, a stop block adjacent to the other end of said spring means, and a tie rod extending between said reaction plate and stop block, and being located within the hollow central position of said spring means.

4. A gripping device according to Claim 3, further comprising a first handle attached to said reaction plate, and a second handle attached to said stop block.

5. A gripping device according to Claim 3 or Claim 4, wherein said link means comprises a sleeve force arm, a bar force arm and wherein said gripping device further comprises a yoke positioned around a first end of said sleeve force arm and simultaneously positioned around a first end of said bar force arm; a yoke pin means for connecting said yoke to the first end of each of said sleeve force arm and said bar force arm; said tie rod extending through said stop block and being attached at one end thereof, to said yoke, and said tie rod extending through said reaction plate at the other end thereof; and means for locking said other end of said tie rod in place through said reaction plate.

6. A gripping device according to any one of Claims 1 to 5 and a sleeve having said second jaw means attached thereto, so that said second jaw is stationary; a movable bar positioned within said sleeve, said bar having said first movable jaw means attached thereto; and said sleeve having a longitudinal slot within which said first movable jaw is located for movement either towards, or away from, said second stationary jaw, so as to grip or to release an object.

7. A gripping device according to Claim 6, wherein the second end of said sleeve force arm is connected to said sleeve, and wherein the second end of said bar force arm is connected to said movable bar.

8. A gripping device according to any one of Claims 5 to 7, further comprising a trunnion plate attached at one end thereof to said sleeve, and means for connecting the other end of said trunnion plate to said stop block, such that said tie rod, said yoke, said sleeve force arm, said sleeve, said trunnion plate and said stop block are continuously interconnected, whereby reciprocating movement of said tie rod causes at least one of said force arms to move through said angle 8 so that said jaws open and close.

9. A gripping device according to any one of Claims 5 to 7, wherein said bar force arm has an L-shaped cross-section said first end of said bar force arm being of narrower cross-section than said second end and connected to said yoke, and said second end of said bar force arm being of wider cross-section than said first end and connected to said movable bar.

10. A gripping device according to Claim 9, wherein said sleeve force arm has an L-shaped cross-section, with said first end of said sleeve force arm being of narrower cross-section than said second end and connected to said yoke, and with said second end of said sleeve force arm being of wider cross-section than said first end and connected to said sleeve.

11. A gripping device according to Claim 10, wherein said second end of said sleeve force arm is of wider cross-section than said second end of said bar force arm, whereby said first end of said bar force arm is nearer to said sleeve, and said first end of said sleeve force arm is farther from said sleeve than is said first end of said bar force arm.

12. A gripping device according to Claim 7, wherein said angle 6 comprises the angle between the longitudinal axis of said bar force arm and the longitudinal axis of said movable bar.

13. A gripping device according to Claim 5, wherein said yoke is an inverted U-shaped, flat top bracket comprising an outside arm contacting said sleeve force arm and remote from said sleeve, an inside arm contacting said bar force arm and adjacent to said sleeve, and a flat top portion connected at a right angle to the top part of each of said outside arm and said inside arm.

14. A gripping device according to Claim 13, wherein said yoke pin is placed in the bottom part of said yoke and simultaneously passes through said outside arm, said sleeve force arm, said bar force arm, and said inside arm, so as to connect said yoke to said force arms, and wherein said tie rod is attached to said flat top portion of said yoke.

15. A gripping device substantially as hereinbefore described and with reference to the accompanying drawings.