GB2152464A - Apparatus for maintaining balance of link mechanism of robot - Google Patents

Abstract

An apparatus for maintaining the balance of a link mechanism of a robot includes a pair of parallel links 10, 22 constituting a part of the link mechanism and support shafts 8, 20 respectively projecting from the links 10, 22. Counterweights 11, 24 which are detachable and adjustable in their mounting positions are respectively fitted on the support shafts 8, 20 so that their centre of mass is eccentric with respect to the axes of the corresponding links 10, 22. <IMAGE>

Description

SPECIFICATION Apparatus for maintaining balance of link mechanism of robot The present invention relates to an apparatus for maintaining the balance of a link mechanism of a robot.

Articulated robots are capable of coping with the need to automatic various cargo-handling operations and to save the labor normally required therefor and are therefore widely used at present in such operations as the transfer, loading and unloading of goods, thus bringing great advantage to cargo handlers. The range of application of articulated robots is still increasing. These articulated robots, however, suffer the following disadvantages: an articulated robot transfers an article to a predetermined position by holding the article in its hand portion, by means of which it is able to grip and release the article, and when doing so an excessively high load may be transmitted to an articulated portion or a link mechanism thereof, causing the balance of the robot as a whole to be lost. In an extreme case, the articulated portion or a part of the link mechanism may be damaged.Further, it may be necessary to increase the power required for operating the link mechanism. In consequence, it is obligatory to increase the size of a prime mover, which fact involves an increase in the size of the robot as a whole. In view of the need to consider a case where the space for installation of the robot at an operation site is limited, any increase in the size of the robot would unavoidably result in causing an obstacle to cargo-handling operations as well as in unreasonable increases in installation costs, running costs, etc.

Accordingly, it is an object of the present invention to prevent any damage to the articulated portion or the link mechanism of the robot which might be caused by an excessively high load on the hand portion.

It is another object of the present invention to prevent any unnecessary increase in the size of the prime mover for driving the link mechanism.

It is still another object of the present invention to facilitate attaching and detaching of the counter weights in relation to the support shafts as well as adjustment of the mounting positions of the counter weights.

To these ends, according to the present invention, there is provided an apparatus for maintaining the balance of a link mechanism of a robot in which counter weights which are detachable and adjustable in their mounting positions are respectively fitted on respective support shafts of a pair of parallel links in the link mechanism such as to be eccentric with respect to the corresponding links.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of an embodiment thereof by way of example, with reference to the accompanying drawings.

Figure 1 is a partly-cutaway vertical sectional view of an essential part of an apparatus in accordance with the present invention; Figure2 is an enlarged sectional view taken along the line ll-ll of Figure 1; Figure 3 is an enlarged sectional view taken along the line Ill-Ill of Figure 1; and Figure 4 is an illustration of an essential part of the apparatus shown in Figure 1,showing how counter weights are respectively fitted on links.

A surface plate 1 is fixed to the surface of a floor plate g. A retainer frame 2 is fixed to the surface of the surface plate 1. A reversible prime mover M1, e.g., a reversible electric motor, is mounted on the upper end of a rotating shaft (not shown) which is rotatably supported in an upright position through a bearing within the retainerframe 2. An underframe3 housing the reversible electric motor M1 is rotatably supported by an upper portion of the retainerframe 2. The underframe 3 further houses another reversible prime mover M2, e.g., a reversible electric motor, disposed in parallel to the reversible electric motor M1. The prime mover M2 rotates a rotating shaft 4 through a chain, a belt or other similar means. The rotating shaft 4 is integral with a support member 5.

Athreaded bar 6 is secured to the upper end of the support member 5 such as to be in an upright position. A lifting member 7 is screwed with an external thread a of the threaded bar 6 at an upper portion thereof. A support shaft 8 is rotatably supported by the lifting member 7 through roller bearings r1, r. Fitting members 9 are respectively secured to intermediate portions of the support shaft 8 by means of key k. Long oval links 10,10 which extend vertically (as viewed in Figure 1) are fitted and fixed at their respective lower ends to the corresponding fitting members 9.Counter weights 11, 11 are respectively fitted on both ends of the support shaft 8 by fixing means 31, such as screws or bolts and nuts, through bushes e1, e1 such as to be detachable and such that a mounting angle a is selectable as desired. It is to be noted that the lower end of a support arm 12 is fixed to the support shaft 8 by being clamped between the fitting members 9, 9. A frame 13 is flange-spliced to the upper end of the underframe 3. A reversible prime mover M3, e.g., a reversible electric motor, is housed and fixed inside the frame 13. The reversible prime mover M3 causes a threaded bar 17 to rotate through a pulley 14, a belt 15 and a pulley 16. A shifting member 18 is screwed on the threaded bar 17. The shifting member 18 is integrally formed with a retainer member 19.A support shaft 20 is rotatably supported by the retainer member 19 through roller bearings r2, r2.

Fitting members 21,21 are fitted and fixed on both ends of the support shaft 20. The respective lower ends of long oval links 22, 22 are respectively secured to the fitting members 21,21. On the respective outer sides of these links 22, 22, short oval links 23, 23 which extend horizontally (as viewed in Figure 1) are pivotally supported at their respective lower portions by the support shaft 20 through roller bearings q, r3.On the other hand, the respective upper portions of the links 23,23 are movably connected to the corresponding links 10, 10 through pins p which project from the respective lower portions of the links 10, 10. Further, counter weights 24,24 are respectively fitted on both ends of the support shaft 20 by fixing means 32, such as screws or bolts and nuts, through bushes e2, e2 such as to be detachable and such that a mounting angle ss is selectable as desired.It is to be noted that it is possible to attach counter weights weighing any desired amount irrespective of the distance d between the links 10 and 22 by making the respective centrl lines W,-W1, W2-W2 of the counter weights 11, 24 eccentric with respect to the respective central lines C1-C1, C2-C2 of the links 10,22. A guide bar 25 is pivotally supported by a support shaft 30 provided at the distal end of the support arm 12. The upper end of the guide bar 25 is movably connected to one (the left end, as viewed in Figure 1) of the ends of a T-shaped joint member J which is pivotally supported by a pin g extending between the respective upper ends of the links 10. A guide bar 26 is movably connected to the other end (the right end, as viewed in Figure 1) of the joint member J.The upper end of a support member S is movably connected to a pin 29 projecting from the distal end of the guide bar 26. A support shaft 27 is horizontally carried and fixed to the support member S. One of the ends of a long link 28 extending horizontally (as viewed in Figure 1) is movably connected to the support shaft 7. The other end of the link 28 is movably connected to the ping.

Further, an intermediate portion of the link 28 is movably fitted on a pin extending between the respective upper ends of the links 22. A reversible prime mover M3, e.g., a reversible electric motor, is installed on the upper portion of the support member S. The lower portion of the rotating shaft (not shown) of the motor is secured to an upper portion of a suspended member T suspended from the lower portion of the support member S, thereby allowing the suspended member Tto rotate with respect to the support member S. Further, the suspended member T is provided on the lower side thereof with scrapers n and fingers u, which are opened and closed by means of a prime mover, suh as an air cylinder (not shown), thereby allowing such operations as the gripping, transfer and stowage of an article V.It is to be noted that all the three support shafts 8,20 and 27 should be aligned with each other, in one straight line, at all times. It is to be noted also that the above-described links 10,22,23 and 28 are, in all, referred to as a link mechanism L.

In the drawings, the reference symbols y1 to y7 represent spacers, while 8, and 62 denote respective eccentric distances in relation to the counter weights 11,24.

In operation, where the suspended member T holding the article V by the scrapers n and the fingers u is at the solid-line position shown in Figure 1, the reversible prime mover M1 is actuated such as to rotate the underframe 3 and all the members thereabove by any desired angle with respect to the retainer frame 2. On the other hand, the reversible prime mover M2 is actuated such as to rotate the threaded bar 6 in the direction of the arrow (in Figure 1), for example, in orderto raise the lifting member 7 through the external thread a. Thereupon, as the links 10 supported by the lifting member 7 are pivoted clockwise (as viewed in Figures 1 and 2), the support member S is lowered through the joint member J, the guide bar 26 and the link 28, whereby the suspended member T is set at any desired position whether or not it is being rotated.Then, the scrapers n and the fingers u are opened by means of the prime mover, such as an air cylinder, thereby allowing the article V to drop or be placed on an article stowed previously, directly below the sus pended member. After the above-described operation has been completed, the reversible electric motors M1, M2 are respectively driven in the directions reverse to the above, whereby the lifting member 7 is lowered such as to return the suspended memberTto the illustrated solid-line position and the underframe 3 is rotated with respect to the retainer frame 2 such as to return to its former position in order to stand by for a subsequent article V.

When the reversible prime mover M3 is actuated such as to rotate the threaded bar 17 in the direction of the arrow (in Figure 1), for example, through the pulley 14, the belt 15 and the pulley 16, as the shifting member 18 screwed on the threaded bar 17 is shifted rightwardly (as viewed in Figure 1), the retainer member 19 is also shifted horizontally rightwardly. Consequently, the suspended member T is also simultaneously shifted horizontally rightwardly. Thus, it will be understood that it is possible to move the suspended member T both vertically and horizontally as desired from the illustrated solid-line position by respectively driving the reversible prime movers M2, M3.It is to be noted that the links 10,22 are simultaneously moved by the operation of the reversible prime mover M2 or M3 while maintaining their parallel state by means of the pins g, fand the link 28.

When the weight of the article V is excessively large and consequently it is difficult to maintain the balance state of the robot as a whole, first of all, the fixing means 31, 32 are loosened at the respective ends of the support shafts 8, 20. Then, the counter weights 11,24 are respectively adjusted to properly selected angles, e.g., a and ss, and are then secured to the respective ends of the support shafts 8,20 again by the fixing means 31,32. Thereupon, the counter weights 11, 24 are respectively fixed such as to be eccentric by 8, and 62 with respect to the respective central lines C1-C2, C2-C2 of the links 10, 22.As a result, the link mechanism Las a whole is in satisfactory balance with the weight of the article V, whereby it is possible to equalize the load throughout the link mechanism L. Further, it is possible to increase the strength of the link mechanism Las a whole and, therefore, it is possible to prevent any damage to the articulated members or the links. In addition, it is possible to respectively attach the counterweights 11, 24 weighting any desired amount to appropriate positions on the support shafts 8,20 irrespective of the distance between the links 10, 22. It is, therefore, possible to constantly maintain the balance of the link mechanism L by applying to the link mechanism La proper means by which it is possible to cope with any change in the weight of an articie V to be handled. Further, it is possible to easily attach and detach the counter weights 11,24 in relation to the support shafts 8,20 through the bushes e1, e2 and, therefore, it is possible to eliminate the need for troublesome work and much time conventionally required for such operation. Furthermore, there is no possibility that the mechanism for maintaining the balance of the link mechanism L may be unnecessary increased in size or complicated. Thus, the present invention offers various advantageous effects.

Claims (6)

1. An apparatus for maintaining the balance of a link mechanism of a robot comprising: a pair of parallel links in said link mechanism; support shafts respectively projecting from re spective lower portions of said links; and counterweights respectively attached to said support shafts such as to be detachable as well as adjustable in their mounting positions and eccentric with respect to the central line of the corresponding links.

2. An apparatus for maintaining the balance of a link mechanism of a robot comprising: support shafts respectively projecting from a pair of parallel links in said link mechanism; bushes fittable on respective ends of said support shafts; fixing means allowing said bushes to be attached and detached in relation to said support shafts; and counterweights respectively fitted on said bushes and able to be attached to respective ends of said support shafts by said fixing means such as to be detachable as well as adjustable in their mounting positions and eccentric with respect to the central lines of the corresponding links.

3. An apparatus for maintaining the balance of a link mechanism of a robot according to claim 1, wherein said pair of parallel links in said link mechanism are installed such as to extend vertically, and said link mechanism further includes: support shafts respectively projecting from respective upper and lower portions of said links; and long and short links movably connected between the upper support shafts and between the lower support shafts, respectively.

4. An apparatus for maintaining the balance of a link mechanism of a robot according to claim 3, wherein said support shafts respectively projecting from said pair of vertically extending links in said link mechanism and a support shaft provided on one of the sides of said long link closer to a support member, said long link movably connecting together respective upper portions of said links, are aligned with each other, in one straight line, at all times.

5. A robot for lifting, comprising a longitudinally extending link which is connected to a rotatable shaft, the link pivoting about the shaft axis, wherein there is provided on the shaft a detachable weight whose centre of mass is not aligned with the axis of the shaft, the weight being mountable on the shaft with its centre of mass in a plurality of positions relative to the longitudinal direction of the link.

6. A robot, substantially as hereinbefore described with reference to the accompanying drawings.