GB2048212A

GB2048212A - Load Handling Grippers

Info

Publication number: GB2048212A
Application number: GB8013250A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1979-04-23
Filing date: 1980-04-22
Publication date: 1980-12-10
Also published as: FR2454878B1; IT1128518B; SE437344B; DE2916312A1; GB2048212B; FR2454878A1; IT8048478A0; SE8002987L; DE2916312C2

Abstract

A gripper comprises a tongs retaining means 4 mounted at one end of the gripper body 1, an actuating rod 2 for the tongs displaceable longitudinally within the body 1 and a pair of levers 6; 7, which constitute the gripper tongs, pivotable, on bearings 12; 13 arranged in the retaining means 4, by means of the actuating rod 2. An abutment 5 is provided on the retaining means 4 for limiting the travel of the rod 2 which is operated by means of a hydraulic cylinder having a control circuit 25. The levers 6; 7 are two-armed levers and are operatively connected to the adjacent end 3 of the actuating rod 2 by way of entraining elements 14; 15 which constitute length equalisation means. The actuating rod 2 is lockable in its operating position by the provision of a non-return valve 26 in the circuit 25. This construction provides advantages in manufacture and application by virtue of wider gripping tolerances and insensitivity to changes in temperature, impacts and to contamination by dust. <IMAGE>

Description

SPECIFICATION Gripper Arm With Gripper Tongs for Handling Apparatus This invention relates to grip tongs for use in handling equipment, preferably constructions which have exchangeable fingers, not only for rotationally symmetrical workpieces, for example, but also for variable gripping geometries and are also suitable for use with heavy loads in the range of elevated temperatures.

The invention starts from the prior art as known, for example, from Literature Reference 1: "Flexibility of Gripper Systems" by B. H. Auer, published in "Werkstatt und Betrieb", 1 1 1 (1978) 6, pp. 377-381.

This citation illustrates in Fig. 3 a gripper principle hitherto preferred for large ranges of flexibility, Section 3.1 analysing its behaviours in accordance with the toggle lever features. It is pointed out inter alia that when a gripper system of this kind grips, the reaction forces inevitably result in a deformation, and that resilient behaviour in relation to the gripping force is another decisive factor determining the field and quality of use. The citation continues: "The resilient effect of the gripping system therefore limits the gripping force. However, it increases the gripping range, since the resilient effect always displaces the working point for objects of relatively large gripping diameter in the direction of a higher gripping force".On the basis of this realisation, an account is given of efforts aimed at extending the working range by introducing possibilities for adjusting the axial distances and self-centring (cf. for example, Figs. 7 and 8).

In addition to the drive principle of the lever transmission and the wedge transmission, another kinematic principle for grippers which is known is the "wheel transmission" (cf. Literature reference 1, Fig. 1). In the prior art constructions this has in the first place the feature, hitherto regarded as a disadvantage in comparison with other kinds of drive, that it does not have an automatic retaining effect in any closed position.

Another disadvantage was that the cost of manufacture of the pinion and rack was high in comparison with lever-transmissions having a few relatively simple bores, and that for reliable operation it required such precise fits of the positive-connectionrnproducing parts that their use would have resulted in jamming at elevated temperatures. Due to the concentration of lines of force, in the case of these two kinds of transmission the heaviest stressing occurs-in the central bearing point via which the halves of the gripper are interconnected. In the case of wheel transmissions the forces extend-- substantially uniformly through the pivot points of the pinions and therefore also through a precisely predictable goemetrical position for every gripper opening angle.

Under the effect of force, the halves of the gripper both tend to take up the same angle in relation to the gripper main axis.

This is also the case if asymmetrical workpieces are to be gripped. However, in that case what easily occurs is one-sided distributions of forces and deformations and load peaks with possible consequent damage such as wear, breakage, etc., or inadequate retaining (holding) forces.

Such resulting damage was observed more particularly in the joints, via which the drive force is initiated. At the same time, the adaptability and loadability of all these gripper transmissions is only narrowly limited as regards dimensions.and forces, and the merely kinematically caused high stressing of the exclusively pivotable joints represents one of the essential marginal conditions for the use of such grippers in hot or aggressive surroundings.

The invention aims at providing on the basis of this prior art a gripper system which combines a high degree of flexibility as regards workpiece geometry and load, a reduced dependence on the symmetry of the object and the deformability of the levers, and also a reduced concentration of forces in the joints, with reduced liability to wear and damage even under hot operating conditions.

Accordingly, the present invention consists in a gripper arm with gripper tongs for handling apparatuses, comprising a tongs retaining means mounted at one end of the gripper arm, an actuating rod displaceable longitudinally of the gripper arm in relation to the retaining means, a pair of levers which constitute the gripper tongs and which are pivotable by means of the actuating -rod, a travel limitation means for the actuating rod, and a linear drive, remotely controllable via end position sensers, for force initiation to displace the actuating rod, characterised in that the levers are two-armed levers and are pivotably mounted on pivot bearings in the retaining means, the levers are articulated by their one arm on the end of the actuating rod adjacent the levers, a length equalisation is provided between the actuating rod and each pivot bearing, and the actuating rod is lockable in its operation position.

The construction of the invention achieves the following advantages: a) the reaction forces meeting at the gripperside end of the actuating rod cause via two entraining elements lower bearing forces than in the case of the central joint of a conventional toggle lever, or in a wedge or wheel transmission, and consequently lower energy loss and wear.

b) The holding force and range of adaptation of the grip tongs are not mainly limited by the lever kinematics but are adaptable to the largest extent via the drive force and are moreover selfreadjusting, something which is only possible at great expense with conventional grippers, if at all.

c) The mouth width of the grip tongs can also still be used even with an angle of +300 from the straight, so that it offers far more possibilities than the toggle-lever principle.

d) There is practically no risk of jamming due to wrongly tensioned levers (e.g., due to high temperatures or one-sided loading).

e) The lever stressing is statically favourable, since no kinking forces can be present with long distances and since moreover the pivot bearings are borne in the retaining system.

f) During gripping, the actuating rod is subjected exclusively to tensile stressing, nor is there any kinking stressing in the rod even with large distances from the adjusting drive to the force-diverting retaining means at the free gripper arm end.

g) The linear drive can therefore be disposed without any problems on the drive-side end of the gripper arm - i.e., adjacent its axis of inclination, where not only does its weight have a lower force-depriving effect, but moreover the cable and hQse connections can be accommodated more advantageously and with better protection.

h) The gripper parts can be very simply manufactured and assembled without any problems, in the same way as wearing parts can be exchanged if necessary. Even with heavily worn bearings and gripping tools there is no risk of an accidental failure of holding force due to static-kinematic reasons.

Advantageous further developments of the invention are described in the subclaims. The optional feature of claim 2 ensures that the lever pair can be used with favourable force transmissions over a wide range of tolerance for the gripping geometry, without having to be reinforced on a large scale.

The optional feature set forth in claim 3 produces favourable bearing forces also in the support of the actuating rod and in the pivot bearings, and the limitation of the actuating rod travel is effected directly by the retaining system, instead of indirectly by levers or bearings, as in the case of the toggle lever.

The optional feature of claim 4 produces a structural form which is very advantageous for manufacture and utilisation, since length equalisation and also rotational entrainment can be effected via the same element and for this purpose no flat surface machining is required, but merely bores and rotating parts.

This optional feature also ensures that the drive-side levers are so articulated in a readily exchangeable manner in the actuating rod via a simple bore, that transverse forces from the load are in practice unable to react on it.

The optional feature set forth in claim 5 ensures that the entraining elements (round pin) can be inserted directly into the levers, without ancillary means and without screws, and can be knocked out again (through the bores extending further outwards) in a very simple manner for exchange, if needed.

The optional feature of claim 6 ensures that th( basic principle of the invention can be applied, with the use of only a few additional elements, even to multiple grippers which are drivably connected to the same actuating rod.

The optional feature set forth in claim 7 ensures that the most important wearing parts of the gripping tongs are exchangeable and the number of variant spare parts can be kept low.

The optional feature set forth in claim 8 ensures that the actuating rod or hydraulic piston can readily be demounted in the direction of the gripper-side end only with the gripper unloaded, that other retaining means and grippers can also be readily slipped on to the same actuating rod, and that there can be no question of the retaining means being accidentally displaced sideways under loading.

The optional feature set forth in claim 9 ensures that with the hydraulic system ensuring high concentrations of forces in a compact space and with low specific weight, actuation can be effected rapidly, reliably and safely in the established manner with presses and the like, while at the same time the basic requirement for infinitely variable pressure adaptation inherent in this gripper lever principle can be met via the initiation of the adjusting force.

The optional features set forth in claims 10 to 14 afford various advantages of control technique and safety enhancement with the particularly preferred embodiment.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Fig. 1 is a part-sectionai plan view of the gripper arm with gripper tongs and adjoining connection to the drive in the gripper arm and with the associated hydraulic circuit, and Fig. 2 is a side elevation of the gripper tongs, indicating in outline the possibility of attachment to a multiple gripper.

As shown in the lower part of Fig. 1, an actuating rod 2, which is longitudinally displaceable in a gripper arm 1, is radially mounted at its end 3, adjacent the gripping means 6;7, in a retaining means 4. Excessive displacement of the actuating rod 2 in the direction of the gripping means and thus excessive opening of levers 6;7, constituting the gripping means, is prevented by an adjustable abutment 5, which is mounted on the retaining means 4 and acts as a travel limitation. The levers 6;7 are two-armed levers and each has a drive arm 8;9 and a driven arm 10;1 1 between which an associated pivot bearing 12;13 having a bearing pin 1 8 is disposed. The actuating rod 2 is positively connected to the levers 6;7 via two independently pivotable and longitudinally movable elongate entraining elements 14;15 and thereby limits the mobility of the revers 6;7. In the embodiment illustrated the entraining elements 14;1 5 used are constructed as pins 1 6 having circular cross-section, each pin being located in a bore 7 in the associated drive arm 8;9, the bores 17 emerging on the other side of the bearing pin 18, so that from this place the pins 1 6 can readily be knocked out if exchange becomes necessary.

The bearing pins 18 of the pivot bearings 1 2;1 3 are preferably mounted in bearing bushes 19 which can also be used for supporting one end of entraining elements 14;1 5, which at their other ends are constructed, in this embodiment, as round-off cams which engage the end 3 of the actuating rod 2.

The upper part of Fig. 1 also shows incorporated in the gripper arm 1 a hydraulic adjusting device 24, preferably used in this embodiment as a linear drive, for longitudinal displacement of the rod 2. The hydraulic adjusting device 24 is supplied from a pressure-holding supply 25 having a self-iocking nonreturn valve 26 which prevents the holding force from dropping off while gripping continues. In this embodiment, end position sensers 27 are provided which are so attached to a window of the gripper arm 1 that they control the position of a signal lug 28 which is movable therealong together with the actuating rod 2. A pressure reducing valve 31 prevents excess pressure or excessive holding force.A control valve 30 guides the oil flow as required, without detours and with minimum energy loss, to the position associated with the open position 0 or hold-shut position of the hydraulic adjusting member 24.

Fig. 2 shows a prolongation 20 of the bearing pin 1 8 and a member 21 attached to the retaining means 4 for a multi-gripper construction which, while using means for rotational entrainment 22, such as clamping pins, has drivably coupled grippers- between the bearing pin 18 and levers 6;7.

Description of Operation The gripper open position 0 is the starting position. When the line Z in the control valve 30 is opened, the hydraulic adjusting device 24 moves the actuating rod 2 into the hold-closed position Z, the pressure being kept constant, since the pressure-holding supply 25 is designed for automatic replenishment. If required, it is possible in a very simple manner also to incorporate a similar modulation of the holding pressure in relation to the required holding force or gripper lever position.

When the actuating rod 2 is pulled (upward as viewed in Fig. 1), the entraining elements 14:15 engaging pivotably and longitudinally displaceable in its end 3 are pulled in the direction of the gripper arm 1 so that the levers 6;7 pivot around the respective pivot bearing 12;13 and the free ends of the entraining elements 1 4;1 5 move a short distance out of the bores 17, in accordance with the arc of a circle around them, the driven arms- 1 0;1 1 on which attaching devices for gripping tools are mounted, being moved towards one another.

The gripper open position 0 can be adjusted automatically even if the power fails. To this end a return spring 32 is located, with pre-stressing in the opening direction of the levers 6;7, between the actuating rod 2 and the interior wall of the gripper arm 1 by means of abutment collars 33 and 34.

The gripping tongs principal of the invention can also be used with different kinds of arrangements for the rotatability and longitudinal mobility of the entraining elements 1 4;1 5. For example, in particular cases articulation to the actuating rod might be effected via hooks and eyes, instead of cam-shaped, rounded-off pins in a common bore, as long as the levers have provision for longitudinal guiding, if the eyeentraining means are attached to the levers.

Claims

1. A gripper arm with gripper tongs for handling apparatuses, comprising a tongs retaining means mounted at one end of the gripper arm, an actuating rod displaceable longitudinally of the gripper arm in relation to the retaining means, a pair of levers which constitute the gripper tongs and which are pivotable by means of the actuating rod, a travel limitation means for the actuating rod, and a linear drive, remotely controllable via end position sensers, for force initiation to displace the actuating rod, characterised in that the levers are two-armed levers and are pivotably mounted on pivot bearings in the retaining means, the levers are articulated by their one arm on the end of the actuating rod adjacent the levers, a length equalisation is provided between the actuating rod and each pivot bearing and the actuating rod is lockable in its operating position.

2. A gripper arm according to claim 1, wherein pivotable entraining elements are provided which interconnect the actuating rod and said levers, the' distance between the pivot bearings and the drive axis of the actuating rod is substantially larger than the distance of the entraining elements from the drive axis, and wherein in the central position of said levers the lines connecting the pivoting axes of the levers with the respective pivoting axis of the entraining elements extend at the same angle to the actuating rod, the distances of the pivoting axes of the entraining elements from said drive axis being identical in said central position,

3.A gripper arm according to claim 1 or 2, wherein the actuating rod is radially mounted in the retaining means, each pivot bearing consists of a pivot pin supported on both sides of the associated levers and wherein the travel limitation means is,an adjustable abutment for the actuating rod, such abutment being connected to the retaining means.

4. A gripper arm according to claim 2 or 3, wherein the driveside ends of the entraining elements are crowned, round-off cams of identical external diameters which are guided pivotably and with provision for limited longitudinal movement in a bore extending through the actuating rod transversely in relation to said drive axis.

5. A gripper arm according to claim 4, wherein the driven-side ends of the entraining elements are constructed as pins having circular crosssection and are located in the transverse bores which are machined in the drive-side arm of the respective lever, substantially parallel with the respective connecting line of the pivoting axes of the levers and the entraining elements and substantially perpendicularly to said drive axis, and emerge freely both to the bore in the pivot bearing and also beyond through the lever.

6. A gripper arm according to any of claims 1 to 5, wherein further levers in a further retaining means are drivably connected in parallel via a member attached to the further retaining means and a bearing pin prolongation to the first levers in the retaining means, and wherein the bearing pins have means for rotational entrainment of said further levers.

7. A gripper arm according to any of claims 2 to 6, wherein the entraining elements and the bearing pins of the two pivot bearings have identical bearing bushes.

8. A gripper arm according to any of claims 1 to 7, wherein the gripper end of the actuating rod is releasably connected via a laterally insertable connecting member to the actuating rod and wherein when the gripper is closed, the connecting member cannot be displaced laterally.

9. A gripper arm according to any of claims 1 to 8, wherein the linear drive is a hydraulic adjusting device which can be locked-in a pressure-holding supply by a self-unlocking nonreturn valve, the end position sensers can be activated without intermediate position by a signal lug on the actuating rod, and wherein the retaining force is controlled by a press switch and can be varied steplessly by means of pressure variation in a pressure-reducer for adaptation to the gripping angle and workpiece dimensions.

1 O. A gripper arm according to claim 9, wherein an end position senser is so associated with the outermost open position (0) and also the outermost hold-shut position (Z) respectively, that the signal lug always approaches from the same direction and therefore without hysteresis, and wherein the sensers are short-circuited in a control circuit with the pressure-holding supply.

1 A gripper arm according to claim 9 or 10, wherein over the whole operating range the operating position of the levers can be monitored via the end position sensers and the press switch, with a fixed adjustment of the required value specific to the gripper in each case, the gripper tongs are in the stand-by position for gripping (completely opened) on a signal from the senser (0), the gripper tongs complete their grip (workpiece clamped) on signal from the press switch, if the gripper tongs fail to grip (no workpiece) a signal is delivered from the senser (Z), and wherein each operating position can be returned to the stand-by position for gripping (senser 0 activated), accompanied by cancellation of the actuating force.

12. A gripper arm according to any of claims 2 to 11, wherein the actuating force on the entraining elements always rernains constant du.ring the completion of gripping, for all workpiece dimensional variants specific to the gripper, in accordance with the required value adjusted at the pressure-reducing valve, and wherein the actuating force and the required value can be altered separately via the pressure reducing valve within displaceable limits.

1 3. A gripper arm according to any of claims 1 to 12, wherein the stroke of the actuating rod can be steplessly limited.inhe direction of the open ; í' - position (0) by an abutment screw central to the drive axis (A) in the travel limitation.

14. A gripper arm according to any of claims 1 to 13, wherein the open position (0) can be adjusted automatically, even if the power fails, 'a return spring being incorporated with pre stressing in the opening direction between the actuating rod and the inside wall of the gripper arm by means of abutment collars.

1 5. A gripper arm with gripper tongs, substantially as herein described with reference to and as-shown in the accompanying drawings.