WO2002006017A1

WO2002006017A1 - Industrial robot device

Info

Publication number: WO2002006017A1
Application number: PCT/SE2001/001541
Authority: WO
Inventors: Åsa VALLIN; Hans Skutberg; Ivan Lundberg; Jan-Gunnar Persson; Mathilda Andreasson; Torgny BROGÅRDH
Original assignee: Abb Ab
Priority date: 2000-07-07
Filing date: 2001-07-04
Publication date: 2002-01-24
Also published as: SE0002576L; SE0002576D0; AU2001267998A1

Abstract

Manipulator arranged with a joint arrangement that includes two parallel link arms.

Description

Industrial robot device

TECHNICAL AREA

The present invention relates to an industrial robot comprising a manipulator and a control system where the manipulator has a number of arms comprising linkage systems where the arms together support a moveable element.

BACKGROUND

An industrial robot comprises a manipulator and control equipment. Industrial robots where the manipulator comprises three arms are named delta robots and a common tool is normally used when the robot is to pickup and move items between two positions/places. For picking up, the usual need is for the robot to be able to move quickly. Another need is normally that the moveable element/tool retains its orientation in space during the movement.

Document US 4 976 582 A shows a delta robot that comprises a manipulator with which a moveable element can be transported in space in relation to a stationary element with retained orientation and retained inclination. The mampulator has three arms in the form of linkage arrangements arranged between the stationary element and the moveable element, together supporting the moveable element. Three driving arrangements each drive its linkage arrangement. The linkage arrangements comprise links and joints, where the joints commonly consist of ball-and-socket joints. The linkage arrangement shown in Fig. 2 comprises three parallel links 5a and 5b joined to pivot with ball-and-socket joints 26a, 26b, 27a and 27b (Fig. 8).

Document WO 97/00434 shows a manipulator with which a moveable element can be transported in space in relation to a stationary element with retained orientation and retained inclination. The document shows a range of embodiments that have arms in the form of linkage arrangements comprising one link, two parallel or three parallel links. All embodiments comprise single axis, double axis and triple axis joints (Fig. 8). In these known joint arrangements, errors are introduced when fitting the balls via rods that are attached to the platform beams. It is difficult to attain high precision when attaching the sockets on the link rods. To increase the ability of a manipulator to move, the actual joint socket of a ball and socket joint must be arranged with a small spherical extension. However, if the socket is arranged as less that a half sphere, the joint will not hold together. An external force must then press together the ball and socket the whole time so that the joint can transfer pushing and pulling forces without loose play.

Document WO 00/27597 shows a part of a linkage system that is included in a mampulator (not shown). Fig. 1 shows parts of two parallel links 1 and 4 joined with ball joints 3 and 6. Both links each comprise a joint socket designed as a half sphere facing the other. Each joint sockets fits over its own ball joint. The joints are held together by a spring arrangement that binds together the links and exerts a pulling force between the links that presses the joints together.

The parallel links together with the connecting links form a parallelogram whose shape changes when the robot pivots. At their respective ends, the parallel links have opposing joint sockets that interact with joint balls arranged in the ends of the connecting links. The joint sockets consist of half spheres and the coupling thus requires an external force that the whole time presses the ball and socket against one another so that the joint can transfer pushing and pulling forces without loose play. A spring arrangement is arranged between the parallel links to achieve the required force of pressure in the joint.

The development of industrial robots is, among other things, moving towards robots with a number of arms built up of multi-linkage systems. Normally, the robot comprises quadruple linkage systems with pairs of parallel links. The development is also moving towards robots with greater movement and larger working areas. One possible path of development is to increase the degree of movement in the ball joints. A robot arranged with joints according to that above has a limited working area as the links can only be angled +/- 30 degrees.

An expressed need within industry is for robots that in operation can handle great accuracy _' and a large degree of rigidity. The spring arrangement according to that above bends the links that thus become pliant for the pushing and pulling forces that are to be transferred by the links. Because of this there is a need to reduce the load on the links so that the bending of them can be eliminated. When a robot pivots so that the links become angled, a force with a direction depending on the angle is obtained. One socket is lifted up and the other is pushed down. Taken together, this leads to the need for a spring arrangement that gives a more advantageous distribution of force in the linkage system.

Even manipulators with multi-linkage systems have the need to increase their degree of move ability and reduce the loading on the links. In multi-linkage systems, two or more links are arranged to pivot without the requirement of being parallel. The distribution of forces becomes complex but the need named above still remains or alternatively is greater.

The precision of the robot decreases rapidly if and when loose play arises in the ball joints. There is thus a need to design ball joints with loose play eliminated and thus with extremely high precision and this at reasonable costs.

In robots with joint arrangements according to known technology (Fig. 15), the joint sockets are arranged transversely in relation to the links. During a collision between a robot and its surroundings, a joint ball is pressed even harder into its joint socket if the collision occurs in the direction of the joint socket. The links are bent and cause a danger for the surroundings. It is therefore desirable to arrange joint arrangements where the links pop off the joint balls if the encounter between then is sufficiently powerful.

When manufacturing and using industrial robots of the type stated above, there thus arises a need for linkage arrangements that have a comparatively large move ability, high precision and that are pressed together by spring force that only provides forces of pressure acting on the joint. This need applies irrespective of whether the linkage arrangement comprises a single link, double or several parallel links, or non-parallel multi-linkage systems. If the robot collides with something in its surroundings, it is desirable that the link pops off the joint ball without being damaged or causing damage. There is also a need to keep down the costs of the joint arrangement.

The ball joints in the document specified above cannot meet these needs.

DESCRIPTION OF THE INVENTION

An industrial robot comprises a manipulator with control equipment. The manipulator in the present invention includes several arms that consist of linkage systems comprising at least one link and joints in which the transfer of forces takes place through pure pushing and pulling forces. The arms are built up of single links, double or multi parallel link arms, or non-parallel multi-linkage systems that allow movements between an actuator arm and a manipulated platform. The word link includes joint connections at the respective ends of the link.

The aim of the present invention is to, in a manipulator defined according to that above, arrange a joint arrangement that is designed so that the working area of the robot increases. The aim is also to arrange a joint arrangement that transfers pure pushing and pulling forces and thus avoids bending of the links. Another aim of the invention is to design joint arrangements with minimised loose play, which gives a manipulator that can work with comparatively high precision. The concept of the invention also includes the possibility that the links pop off the joint balls if the arm system collides with its surroundings. This ensures that anyone who happens to be in the vicinity of the robot will not come to harm.

The solution according to the invention is characterised by the manipulator specified in claim 1 comprising a first arm element and a second arm element bound together with a linkage system comprising at least one link that has a ball joint at one of its ends. The ball joint comprises a joint ball and a joint socket attached at one end of the link. A spring arrangement is arranged to exert a pressure force F that presses the joint socket against the joint ball. In all positions, pressure force F is brought to act in a direction along the centre axis A of the link through the centre B of the joint ball. The words "at least one link" refer to linkage systems comprising alternatively single links, double or multi-parallel links, or alternatively non- parallel multi-linkage systems. The words "has a ball joint at one of its ends" refer to at least one of the joints in the linkage system being a ball joint designed in accordance with the invention. These linkage systems can thus comprise different types of joint arrangements.

The spring device and the ball joint according to the invention are arranged in accordance with the dependent claims. The manipulator is manufactured so that the force of the spring arrangement always goes in the same direction in accordance with the independent method claim. A manipulator in accordance with the invention is suitable for use in applications that require high precision, in accordance with the independent use claim.

In the linkage arrangement according to the invention, a link can be angled to +/- 80 degrees in all directions in a ball joint. The forces that arise when pivoting the manipulator act only in the length direction of the link and these are thus not bent. The links can thus better handle the acting pushing and pulling forces.

A ball joint according to the invention comprises a joint ball and a joint socket. The joint ball is attached in a through-hole in an arm element. The hole is made with very high precision in a numerically controlled (NC) machine. The word hole refers to a circular hole. The joint ball consists of a ball of great accuracy. The joint socket is arranged axially in the end of a link and, in one preferred embodiment, consists of the end of a tube. Together, the joint ball and the joint socket form a joint with three degrees of freedom, that is comparatively cheap to manufacture, and that has a very high precision. The position of the centre of the joint can easily be obtained with an accuracy of 1 micrometer.

According to one advantageous embodiment of the invention, a spring arrangement is arranged between and essentially parallel with the links. The spring arrangement comprises a pulling or a compression spring.

According to another advantageous embodiment of the invention, the spring arrangement is divided into two identical arrangements, one in each end of the linkage system. This type of embodiment is especially suitable for long links. The arrangement comprises yoke elements in the form of double yokes arranged in a jointed way transversely across and close to the respective link. The spring arrangement acts on the yoke element and pulls it towards the arm element, whereby the joint sockets are pressed against the joint balls. The aim of the double yoke is that the force shall act along the centre line. The spring arrangement comprises a pulling or a compression spring that is attached with the help of a wire. The wire is made of steel wire or Kevlar, for example. Alternatively, the wire consists of thin rods of metal or fibre-reinforced plastic and that is mounted at double-axis joints on the beams on which the joint balls are mounted. The wire is arranged through a through-hole in the arm element and a membrane covers the opening of the hole. Depending on the environment in which the robot is to work, different materials are chosen for the membrane, e.g. metal or Teflon. In applications with high hygienic demands, the spring chamber must be completely enclosed. The wire must then be attached in the lead-through.

It is included in the concept of the invention that universal/cardan joint links are used on both sides of the spring arrangement to avoid wear of the attachment wire when it is bent against its attachment. Alternatively, two serially coupled joints are used, as accuracy is not critical for the wire attachment.

According to a further embodiment of the invention, the yoke elements named above are resilient and consist of a double leaf spring. The leaf spring is joined to pivot with the arm element via a universal link and a universal coupling. A single axis joint connects the resilient beam with the universal/cardan connection. The concept of the invention includes that the leaf spring has different forms.

According to a further embodiment of the invention, the linkage system comprises a single link that is joined to pivot with a yoke element and is arranged between two pushing and/or pulling springs that are part of a spring arrangement.

According to one embodiment of the invention, the linkage system comprises three parallel links joined to pivot between two arm elements in triangular form. A spring arrangement is arranged primarily parallel with the links and its force of pressure acts along an axle through the point of balance of respective triangle.

Within the concept of the invention there is room for a joint socket arranged inside the end of a tube, for a joint socket in the form of a short tube blank coaxially attached in the end of a link rod, and for a joint socket that is formed from the sawn-off end of a hollow link tube provided with a protecting ring. The concept of the invention also includes that different types of joints, of which at least one is a ball joint according to the invention, are included in a linkage system. In addition, the concept of the invention also includes the variant that the joint socket and the joint ball have exchanged places so that the joint ball is arranged at the end of the link and the joint socket consists of a through-hole in the arm element.

This description should not be seen as a limitation of the invention but only as a guide to a full understanding of the invention. Adaptation to manipulators that include other active parts plus the replacement of parts and details that are obvious for a person skilled in the art can naturally be made within the concept of the invention.

DESCRIPTION OF THE FIGURES The invention will be described in more detail through the description of an embodiment with reference to the attached drawings where:

Fig. 1 shows a part of a linkage system where two parallel links, joint arrangements and spring arrangements are arranged according to the invention,

Fig. 2 shows the linkage system according to Fig. 1 with the different component parts that are included in the joint arrangement according to the invention, Fig. 3 shows the joint ball mounted on the respective arm element,

Fig. 4a shows a joint socket in the form of a short tube blank coaxially attached in the end of a link rod,

Fig. 4b shows a joint socket in the form of a ring firmly arranged in the end of a tube,

Fig. 5 shows a joint socket in the form of a joint socket arranged in the end of a link in the form of a tube, Fig. 6 shows a ball joint where the joint ball is attached in the end of a link and the joint socket is arranged in an arm element,

Fig. 7 shows the spring arrangement divided into two spring elements according to one embodiment of the invention, Fig. 8 shows how the spring arrangement according to Fig. 4 is attached to the respective arm element, Fig. 9 shows a section AA in Fig. 4 where a double beam is arranged on either side of and arranged to pivot with the respective link arm, Fig. 10 shows an embodiment where the beam element is a leaf spring that is joined to pivot with the respective arm element in a universal coupling, Fig. 11 shows a spring arrangement for a single link, Fig. 12 shows a linkage arrangement with three parallel links, Fig. 13 shows known technology in the form of a delta robot, Fig. 14 shows known technology in the form of a manipulator, Fig. 15 shows known technology in the form of a spring arrangement that is arranged between and connects together two parallel links.

DESCRIPTION OF EMBODIMENTS

A manipulator (not shown) comprises a linkage system 1 with two parallel links 2, 3 that connect a first arm element in the form of a first beam 4 arranged on an actuator arm 5 with a second arm element in the form of a second beam 6 arranged on manipulated platform 7 (Fig. 1). The first link 2 is at a first end 8, is joined to pivot with the first beam 4 in a ball joint 9 and at its second end 10 is joined to pivot with the second beam 6 a ball joint 11. The second link 3 is at a first end 12, is joined to pivot with the first beam 4 in a ball joint 13 and at its second end 14, is joined to pivot with the second beam 6 a ball joint 15. Links 2, 3 are parallel and have the same length. In the figure, the first beam 4 and the second beam 6 are arranged parallel and, together with the links, form a parallelogram. Joints 9, 11, 13 and 15 are identical ball joints where each one consists of a joint ball 16 arranged on the first beam 4 / second beam 6 and a joint socket 17 coaxially arranged at each end of the first 2 / second 3 links. Links 2 and 3 are here designed as hollow tubes 18, which is why joint socket 17 consists of the sawn-off end 19 of the tube provided with a protecting ring 17c.

As links 2 and 3 are parallel, the distance between the joints 9 and 13 as well as 11 and 15 is the same. A first spring holder 20 is firmly arranged between the joints 9 and 13 on the first beam 4. A second spring holder 21 is firmly arranged between the joints 11 and 15 on the first beam 6. A spring arrangement 22 in the form of a pulling spring 22a is held by tension, with the help of wires 23, between the first 20 and second 21 spring holder and thus parallel with links 2, 3. The attachment of the spring arrangements shall lie at the level of the centres B of the joint balls (see dashed line in Fig. 2).

From Fig. 2, it is evident how the different components in the joint system are mounted in relation to one another. Here the spring arrangement consists of a compression spring 22b.

Joint ball 16 is firmly mounted at the first beam 4 respective second beam 6 according to the following (Fig. 3). The respective beam is designed with a NC-machined hole 24 for each joint ball 16. The hole is sized so that at mounting, the joint ball rests against the beam slightly embedded in the hole 24 and thus leaving room for the tube in all positions. The precision in the joint comes from the abutment of the ball against the hole where both surfaces are designed with high accuracy. Joint ball 16 is provided with a threaded bolt 25 that, when mounting of the joint, is arranged through hole 24. On the side of each beam opposite to the joint ball, the joint ball is tightened with a nut 26, which gives a simple attachment with high precision. The attachment procedure means that there is no risk that the joint ball can move.

The links 2, 3 are designed as rods in the form of hollow tubes and the joint socket consist of the sawn-off end of the tube. The joints thus consist of the end of a tube that is pressed against the joint ball with the help of a spring arrangement 22. The spring arrangement 22 is arranged so that it exerts a force of pressure that is always brought in the same direction irrespective of the angle of the joint. The force of pressure acts in the direction from the centre axis A of the link arm in towards the centre B of the joint ball (Fig. 3). An alternative embodiment is a joint socket shaped as a half sphere 17a firmly attached inside the end of a tube (Fig. 5). Another alternative is a joint socket in the form of a short tube blank 17b coaxially attached in the end of a link rod (Fig. 4b). A further alternative is a ring 17c arranged in the end of a link tube.

In one embodiment of the invention, the joint socket 17 and the joint ball 16 have exchanged places in the joint arrangement through the joint ball being firmly attached at the end of the link and the joint socket consisting of a through hole in an arm element (Fig. 6).

In one embodiment of the invention with long links, the joint system is complemented both at the first beam 4 and the second beam 6 with identical double yokes 27a and 27b plus spring arrangement 28a and 28b (Fig. 7), one of which is described in the following. A double yoke 27b is arranged parallel with beam 6 and at its ends is joined to pivot with respective links 2 and 3 in single axis joints 30. The double yoke consists of two parallel yokes 31a and 31b each arranged on either side of links 2 and 3. Between yokes 31a, 31b and in the middle between joints 30 there is an end 34 of a wire 33 fixed in a wire attachment 35 (Fig. 9). The wire 33 is connected with the spring device and together they pull the double yoke towards the beam 6 and thereby press and tension together the joints 9,11 / 13,15 (Fig. 7). This is achieved through the wire 33 being drawn from the wire attachment 35 through a through- hole 36 in the beam 6, over a breaker block 37 so that it continues in a direction primarily parallel with the beam 6 and continues onwards until it is attached in a first end 38 of a compression spring 39a (Fig. 8). Compression spring 39a is arranged essentially parallel with the beam 6 and at its second end 40 is attached to an attachment 41 on the side of the beam 6 that is opposite to the joints. A protective casing 42 encloses the spring chamber and is arranged to cover and protect one of the openings 43 of the through-hole 36, the wire 33, the breaker block 37 as well as the compression spring 39a and its attachment 41. A membrane 44 is arranged to cover the other opening 45 of the through-hole 36. The membrane is provided with a hole 44a through which the wire 33 runs. The hole 44a is designed with the precision that the application requires. The embodiments according to the invention shown in figures 7, 8, 9, and 10 require a spring arrangement with two springs while the embodiment according to figure 1 can be designed with a single link and just one spring.

Fig. 10 shows an embodiment where the double yoke 27 is replaced by tensioning double leaf springs 46a and 46b (not shown) in each end of the linkage system, whereof one end is shown. The double leaf spring 46 is joined to pivot with links 2,3 in joint 30a and with the beam 6 via a single axis joint 48, a universal link 47 and a universal joint 47 between joints 9,11 respective 13,15.

Fig. 11 shows an embodiment with a spring arrangement for a single link in a linkage system. The link is connected with a yoke in a single axis between two compression/pulling springs.

Fig. 12 shows an embodiment with a linkage system comprising three parallel links in triangular formation. The spring arrangement that acts in the joint system and presses the joints together is firmly arranged so that its force of pressure acts along a straight line through the point of balance (TP) of the triangles formed.

Claims

1. Manipulator comprising a first arm element (4) and a second arm element (6) joined together through a linkage system comprising at least one link (2,3) where the link at one of its ends, (8,10,12,14) has a ball joint (9,11,13,15) where the ball joint comprises a joint ball (16) and a joint socket (17), as well as a (spring arrangement (22,28,46) that is arranged to exert of force of pressure (F) that presses the joint socket (17) against the joint ball (16) characterised in that the force of pressure (F) is arranged in a direction along the centre axis (A) of the link (2,3) through the centre (B) of the joint ball (16) for all positions of the link (2,3).

2. Manipulator according to claim 1 characterised in that the joint socket (17) consists of a tube element (19) arranged coaxially with the link (2,3).

3. Manipulator according to any of claims 1-2 characterised in that the link arm (2,3) comprises a hollow tube (18).

4. Manipulator according to claim 3 characterised in that the joint socket (17) consists of the end (19) of the tube (18).

5. Manipulator according to claim 3characterised in that the joint socket (17) is designed as a half sphere (17a).

6. Manipulator according to any of claims 1-5 characterised in that the spring arrangement (22) is arranged parallel with the links (2,3) between a first spring holder (20) arranged on the first arm element (4) and a second spring holder (21) arranged on the second arm element (6.)

7. Manipulator according to claim 6 characterised in that the spring arrangement (22,28) comprises a pulling spring (22a).

8. Manipulator according to claim 6 characterised in that the spring arrangement (22,28) comprises a compression spring (22b, 39a).

9. Manipulator according to any of claims 1-5 characterised in that the spring arrangement (22) comprises a first spring element (28a) arranged between a first double yoke (27a) and the first arm element (4), a second spring element (28b) arranged between a second double yoke (27b) and the second arm element (6) where the first (27a) and second (27b) double yoke each join together the links (2,3) and are arranged parallel with the arm elements (4,6).

10. Manipulator according to claim 9 characterised in that the first (27a) respective second (27b) double yoke comprises two parallel yokes (31a,b).

11. Manipulator according to claim lOcharacterised in that the yoke (31 a,b) are jointed arranged with the respective link (2,3) in single axis joints (30).

12. Manipulator according to claim 9 characterised in that the first (27a) respective second (27b) double yoke is designed to be resilient in a direction parallel with the links (2,3).

13. Manipulator according to claim 12 characterised in that the first (27a) respective second (27b) double yoke comprises a double leaf spring (46a,46b).

14. Manipulator according to any of claims 12-13 characterised in that the tensioning beam element (27a,27b) is joined to pivot with the arm element (4,6) in a double axis joint (47).

15. Manipulator according to any of claims 1-14 characterised in that the joint ball (16) is arranged on the arm element (4,6) and the joint socket (17) is arranged in the end (8,10,12,14) of the link (2,3).

16. Manipulator according to any of claims 1-14 characterised in that the joint socket (17) is arranged on arm element (4,6) and the joint socket (16) is arranged in the end (8,10,12,14) of the link (2,3).

17. Method for manufacturing a manipulator comprising a first arm element (4) and a second arm element (6) joined together through a linkage system comprising at least one link (2,3) where the link at one of its ends, (8,10,12,14) has a ball joint (9,11,13,15) where the ball joint comprises a joint ball (16) and a joint socket (17), as well as a spring arrangement (22,28,46) that is brought to exert of force of pressure (F) that presses the joint socket (17) against the joint ball (16) characterised in that the force of pressure (F) acts in a direction along the centre axis (A) of the link (2,3) through the centre (B) of the joint ball (16) for all positions of the link (2,3).

18. Method according to claim 17characterised in that the arm element (4,6) is brought to include a through-hole (36).

19. Method according to claim 18 characterised in that the hole (36) is shaped by a NC-machine.

20. Method according to any of claims 17-19 characterised in that the joint socket (17) is brought to comprise a tube element (17b) arranged coaxially with the link (2;3).

21. Method according to any of claims 17-19characterised in that the link (2,3) is brought to comprise a hollow tube (18).

22. Method according to claim 21 characterised in that the joint socket (17) is brought to comprise the end (19) of the tube (18).

23. Method according to claim 21 characterised in that the joint socket (17) is brought to comprise a half sphere element (17a) that is arranged within the end of the tube (18).

24. Method according to any of claims 17-23 characterised in that the joint ball (16) is brought to be arranged on the arm element (4,6) and the joint socket (17) is brought to be arranged at the end (8,10,12,14) of the link (2,3).

25. Method according to any of claims 17-23 characterised in that the joint socket (17) is brought to be arranged on arm element (4,6) and the joint socket (16) is brought to be arranged at the end (8,10,12,14) of the link (2,3).

6. Use of a manipulator according to claims 1-16 or a method according to claims 17-25 for high precision applications.