WO2001085404A1

WO2001085404A1 - Supplying energy to the end tool, with an endless band, to an industrial robot

Info

Publication number: WO2001085404A1
Application number: PCT/SE2001/001032
Authority: WO
Inventors: Ove Kullborg
Original assignee: Abb Ab
Priority date: 2000-05-11
Filing date: 2001-05-11
Publication date: 2001-11-15
Also published as: AU5692801A; SE0001744D0; SE0001744L

Abstract

The present invention concerns an industrial robot comprising a base (2, 24) to which the lower arm is arranged to rotate around a first axis (A), an upper arm (8, 20) rotatably arranged to a second axis (B) at the lower arm (6, 22), a wrist joint (10, 28) that can be rotated by the upper arm and is supported at a joint (C, E) at the outer free end (12, 30) of the upper arm, at which wrist joint is arranged a turning means (14, 32) for fixation of a tool, a driving means arranged in the lower arm or in the base, which driving means transfers by a transmission a rotational motion from the driving means to the wrist joint. The said transmission comprises a belt transmission (26, 38, 106) with an endless belt arranged at a driving shaft (34) of the driving means, whereby the belt extends essentially along the complete longitudinal extent of the upper arm and where the belt is arranged at the wrist joint at the outer free end for transmission of a rotational motion to the tool. The present invention also concerns a method for an industrial robot, and a use of a belt transmission.

Description

Supplying energy to the end tool, with an endless band, to an industrial robot

TECHNICALAREA

The present invention concerns an industrial robot, a method for an industrial robot, and a use of a belt transmission, according to the device or the method, in a welding process.

THE PRIOR ART

The use of industrial robots for the automation of processes such as welding processes in industry is very common. Such a welding process may, for example, be arc welding of items in the motor industry, where welding work is carried out by small industrial robots with a relatively low total weight equipped with welding guns that also are intrinsically of low weight. It is a characteristic of this type of work, carried out by an industrial robot, that there are no large loads, and it is desired that the total weight of the industrial robot remains low.

It is desired that the centre of gravity remains low, in order to give the said type of industrial robot increased mobility and increased lifetime, and also to achieve simpler driving for rotational motions of the various movable robot arms, which are arranged to rotate about shafts. A high centre of gravity has a negative influence on the driving of the shafts, in particular the lower shafts on the robot, such that the robots obtain decreased mobility, speed and lifetime. For this reason, it has been known for around a decade to place the motors and gears for these lightweight robots far down within the industrial robot, for example, in a base unit, whereby the industrial robot obtains a low centre of gravity. Thus, transmission of power must be carried out by some form of transmission from a motor or gear, in order to transfer a rotational motion to a tool, such as a welding gun, located at the free outer end of the robot arm.

The construction of the robot arm from a number of connected concentric rings that can be rotated relative to each other is previously known. Although it is true that it is possible to transfer a rotational motion from a motor placed far to the rear of the arm to a tool at the other end of the arm using such a robot arm constructed from concentric rings, the robot arm at the same time becomes unreasonably high, which is the reason that this design is not interesting for lightweight industrial robots, in which it is desired to obtain a low centre of gravity and low weight. The use of link rods and chain drives as transmissions in robot arms has been known since the 1970s. Not only do these transmissions contribute to a considerable increase of weight of the robot and a higher centre of gravity, but they also make it impossible for a robot arm, in particular the upper arm, to achieve a further rotational motion, around its own longitudinal axis. Such a rotational motion of an upper arm is normally approximately +/- 60°. This is currently a property that is becoming ever more common and that is desired for industrial robots within automated processes, in particular for industrial robots of an anthropomorphic type, that is, a category of industrial robot with a mechanical system that makes possible motions of the robot arm that are similar to human motions.

DESCRIPTION OF THE INVENTION

It is an intention of the present invention to achieve an industrial robot that has a low weight and low centre of gravity, and that at the same time permits the execution by a robot arm of rotational motions around its own longitudinal axis. Further, it is an intention to give an industrial robot increased mobility, speed and a longer lifetime. It should be possible to execute rotational motions of the robot arms at high speeds and high accelerations, and with relatively high torques. A further intention is to achieve an industrial robot that is reliable in use and cost-efficient from the point of view of manufacturing. Such an improved device for an industrial robot that solves the above-mentioned problems should also be simple to assemble and/or exchange, and it should be advantageous from the point of view of repair.

The solution is achieved with an industrial robot that has the properties defined in claim 1. To be more precise, the current invention concerns, according to claim 1, an industrial robot comprising a base to which the lower arm is arranged to rotate around a first axis. An upper arm is arranged to rotate around a second axis to the lower arm. Further, the industrial robot comprises a wrist joint that can be rotated supported by the upper arm at a joint at the outer free end of the upper arm. A turning means is arranged at the wrist joint for fixation of a tool, a driving means is arranged in the lower arm or in the base, which driving means transfers by a transmission a rotational motion from the driving means to the wrist joint. The said transmission comprises a belt transmission with an endless belt arranged at a driving shaft of the driving means, whereby the belt extends principally along the complete length of the upper arm and where the belt is arranged at the outer free end to the wrist joint for transmission of a rotational motion to the tool.

The advantage of the present invention is that an industrial robot with low weight and low centre of gravity is achieved. Furthermore, the present invention makes it possible for an upper arm of an industrial robot to be allowed to execute rotational motions around its own longitudinal axis. At the same time, an industrial robot is achieved that possesses improved driving of, in particular, the lower shafts of the robot due to a lower total weight and low centre of gravity, whereby the robot arms achieve improved mobility. The belt transmission specified by the present invention has the advantage that it comprises a robust and functionally reliable device. In this way, the total lifetime of the robot is increased.

According to one preferred embodiment, the industrial robot according to the present invention is of the type in which an upper arm of the robot is permitted to execute rotational motions around its own longitudinal axis. Such an industrial robot according to the preferred embodiment can be of the anthropomorphic type.

The belt transmission comprises an endless, continous belt that extends within the robot arms. In order to achieve torque, in a manner that is advantageous from the point of view of weight, from a driving means placed in the robot's base or lower arm, it is appropriate according to one preferred embodiment of the present invention to use a belt of a metallic material with high strength. In this way, the belt is only required to have a thickness of a few tenths of a millimetre. The belt is preferably of steel. However, the belt may also be of a strong non- metallic material, or of a non-metallic material reinforced with metal wires. Examples of non- metallic materials that may be suitable are carbon-fibre or fabric reinforced with glass-fibre (Kevlar). The belt may thus be produced from carbon fibre, fabric reinforced with glass-fibre, and/or metallic material such as steel, or from some mixture of these. It is appropriate if the width of the belt is from approximately 0.5 mm up to some centimetres.

By ensuring a low centre of gravity and a method of achieving torque from a driving means that is advantageous from the point of view of weight, the properties of the industrial robot can be further improved since the driving means is, according to one preferred embodiment of the present invention, placed in the base of the robot. The belt that comprises part of the belt transmission is arranged around driving wheels connected to a driving means, and to driving wheels arranged in a wrist joint in the upper arm of the robot for transmission of a rotational motion. If an output motion on the driving wheels is less than approximately 90°, the belt can be fixed attached to both or to one of the driving wheels. In the case in which an output motion of more than approximately 90° is desired for the driving wheels, a belt cannot be fixed attached to the driving wheels. Since the belt is to be loosely arranged, and only supported around the perimeter of the driving wheels, there is a great risk that slippage occurs between the belt and the surface of the driving wheel. This can be solved by achieving a very high friction between the belt and the surface of the driving wheel. On the other hand, according to one appropriate embodiment of the present invention, a driving wheel can comprise around its perimeter a number of pins protruding from the driving wheel, evenly distributed with respect to each other. A belt from the belt transmission has corresponding depressions along its surface into which the pins can be introduced and removed and in this way collaborate with the belt.

The present invention also comprises a method for production of an industrial robot comprising a base to which the lower arm is arranged to rotate around a first axis. An upper arm is arranged to rotate around a second axis to the lower arm and the upper arm supports a wrist joint that can be rotated at a joint at an outer free end of the upper arm. A turning means for the attachment of a tool is arranged at the wrist joint. A driving means is arranged in the lower arm or in the base, which driving means, transfers, by a transmission, a rotational motion from the driving means to the wrist joint. The transmission is arranged to comprise a belt transmission with an endless belt that is arranged at a driving shaft of the driving means. The belt is arranged to extend principally along the complete length of the upper arm and the belt is further arranged at the outer free end to the wrist joint for the transmission of a rotational motion to the tool.

The present invention also comprises a use of a belt transmission, according to the above- mentioned device or method, in a welding process, such as, for example, arc welding.

The industrial robot that has been described according to the present invention, which can also be denoted by "manipulator with control device" is of a type intended to be able to support loads up to a least some hundred grams, and suitably, up to at least 1 kg. "Rotation of the robot arm", as mentioned in this document, also describes the execution of a rotational motion by the robot arm.

DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail in the form of a non-limiting embodiment, made clear by the use of the attached drawings in which:

Fig. 1 provides in side view a sketch of the principle of an industrial robot,

Fig. 2 shows schematically in cut-away side view a belt transmission arranged in an upper arm and a lower arm for an industrial robot,

Fig. 3 shows a section of a cut-away side view of a driving wheel according to one embodiment.

DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates in a general sketch an industrial robot 1, which may be of an anthropomorphic type, comprising a base 2 placed onto a support 3, at which base is arranged a vertically jointed arm system 4. The arm system comprises a lower arm 6 that is arranged to rotate around a first axis A in the base 2. An upper arm 8 is arranged in what is known as a "arm joint" at the lower arm 6 in a manner that allows it to rotate around a second axis B, and a wrist joint 10 that can be rotated by the upper arm 8 is supported at a joint C at the outer free end 12 of the upper arm, at which wrist joint is arranged a turning means 14 for fixation of a tool (not shown). Driving means (not shown) can transfer power directly to the intended axis of rotation or by a transmission that transfers power.

Fig. 2 shows schematically an upper arm 20 and a lower arm 22 arranged at a base 24 of an industrial robot. It is appropriate that the industrial robot is of an anthropomorphic type. The lower arm 22 is arranged to rotate around a first axis A in the base 24. A belt transmission 26 is arranged in the upper arm 20 and the lower arm 22, and it is appropriate that this is laid internally in cavities in the arms 20, 22. The upper arm 20 is arranged at the lower arm 22 in a manner that allows rotation around a second axis B. As is shown in Fig. 2, the belt transmission 26 can be arranged along the complete longitudinal extent of the lower arm 22. In this way, a driving means (not shown) is arranged in the base 24 and transfers, by the belt transmission 26, a rotational motion from the driving means to a wrist joint 28, supported at a joint at the outer free end 30 of the upper arm 20. The belt transmission 26 extends along the complete longitudinal extent of the upper arm 20, and where the belt transmission is arranged at the outer free end 30 to the wrist joint 28 for transfer of a rotational motion to a tool (not shown). A turning means 32 is arranged at the wrist joint for fixation of the tool. A driving shaft 34, attached to a first driving wheel 36, is arranged at the driving means, which may be a motor or a gear (toothed wheel). The driving shaft 34 and the first driving wheel 36 are concentrically arranged around the first axis A. The belt 38 that is part of the belt transmission is arranged around the perimeter of the first driving wheel 36. The belt 38 consists of an infinite, continuous belt. The belt 38 runs along the longitudinal extent of the lower arm from the first driving wheel 36 over a supporting wheel 40, also known as a "break wheel". This supporting wheel 40 is arranged concentric to the second axis B to which the upper arm 20 is arranged at the lower arm 22 in a manner that allows rotation. Both sides 42, 44 of the belt 38 are arranged at the same side and along the same section 46 of the perimeter of the support wheel 40. However, it is not appropriate that the sides 42, 44 of the belt are arranged in contact with each other, but are arranged next to each other along the perimeter of the supporting wheel, side by side, separated by a dividing wall arranged around the perimeter of the supporting wheel. Furthermore, the belt transmission 26 extends along the complete longitudinal extent of the upper arm 20 to the wrist joint 28, where the belt 38 is arranged around the perimeter of a second driving wheel 48. The upper arm 20 is arranged in a manner that permits rotation also around its longitudinal extent around a third axis D. In this way, a front section 52 and a rear section 54 are connected in a coupling 50, and arranged to rotate relative to each other. One joint for the wrist joint 28 that can be rotated constitutes a fourth axis E. Since the upper arm 20 can execute a turning motion, a rotation, around the third axis D, the support wheel 40 can act as a spring such that the belt 38 is to be held stretched for the complete duration of rotational motions. Thus, a stiff, short spring 56 is arranged at the supporting wheel and arranged at the inner surface of one of the robot arms 20, 22. Fig. 3 shows according to one embodiment of the present invention a driving wheel 100 (generally in agreement with the driving wheels 36, 48 that are displayed in Fig. 2). The driving wheel comprises along its perimeter 102, its periphery, a number of pins 104 equally space relative to each other and protruding from the diving wheel. A belt 106 from the belt transmission has equivalent depressions along its surface into which the pins 104 can be inserted and removed when the belt 106 is applied to and removed from the driving wheel 100. It is particularly appropriate according to this embodiment, that the belt 106 be comprised of a durable metallic material such as a steel belt, since the pins 104 give a significant hole edge pressure against the edges of the depressions during rotation of the driving wheel 100 when the pins are inserted into the depressions of the belt 106. Alternatively, the depressions of the belt, in cases in which the belt consists, at least partially, of a non-metallic material, can be reinforced by a ring of durable, metallic material. The pins 104 should also be made of a durable, metallic material in order to withstand the loads that arise on them.

Claims

1. An industrial robot (1) comprising a base (2, 24) at which a lower arm (6, 22) is rotatably arranged to a first axis (A), an upper arm (8, 20) rotatably arranged to a second axis (B) at the lower arm (6, 22), a wrist joint (10, 28) that can be rotated by the upper arm and is supported at a joint (C, E) at an outer free end (12, 30) of the upper arm, at which wrist joint is arranged a turning means (14, 32) for fixation of a tool, a driving means arranged in the lower arm or in the base, which driving means transfers by a transmission a rotational motion from the driving means to the wrist joint, characterised in that the said transmission comprises a belt transmission (26, 38, 106) with an endless belt (38, 106) arranged at a driving shaft (34) of the driving means, whereby the belt (38, 106) extends essentially along the complete longitudinal extent of the upper arm and where the belt is arranged at the wrist joint at the outer free end for transmission of a rotational motion to the tool.

2. The industrial robot according to claim 1, characterised in that the said driving means is arranged in the base of the robot (2, 24).

3. The industrial robot according to claim 1 or 2, characterised in that the belt transmission comprises a belt (38, 106) that comprises carbon fibre, material reinforced with a glass-fibre or a metallic material, preferably steel, or some mixture thereof.

4. The industrial robot according to any one of the preceding claims, characterised in that the upper arm (8, 20) is in its longitudinal extent arranged to rotate around a third axis (D), whereby said joint (C, E) of the the wrist joint (10, 28) constitutes a fourth axis.

5. The industrial robot according to any one of the preceding claims, characterised in that the industrial robot is of an anthropomorphic type.

6. The industrial robot according to any one of the preceding claims, characterised in that a supporting wheel (40) is arranged concentric with the second axis (B), whereby the supporting wheel is arranged in a flexible way.

7. The industrial robot according to any one of the preceding claims, characterised in that a first driving wheel (36) is arranged at the driving shaft (34) and that a second driving wheel (48) is arranged at the wrist joint, around the perimeters of which driving wheels the belt (38, 106) is arranged.

8. The industrial robot according to claim 7, characterised in that the said driving wheels (36, 48) are provided with pins around their perimeters (102).

9. A method for the production of an industrial robot (1) comprising a base (2, 24) at which a lower arm (6, 22) is rotatably arranged to a first axis (A), ), an upper arm (8, 20) rotatably arranged to a second axis (B) at the lower arm (6, 22), a wrist joint (10, 28) that can be rotated by the upper arm and is supported at a joint (C, E) at an outer free end (12, 30) of the upper arm, at which wrist joint is arranged a turning means (14, 32) for fixation of a tool, a driving means arranged in the lower arm or in the base, which driving means transfers by a transmission a rotational motion from the driving means to the wrist joint, characterised in that the transmission is arranged to comprise a belt transmission (26, 38, 106) with an endless belt that is arranged at a driving shaft (34) of the driving means, whereby the belt (38, 106) is arranged to extend essentially along the complete longitudinal extent of the upper arm and where the belt is arranged at the wrist joint at the outer free end for transmission of a rotational motion to the tool.

10. The use of a belt transmission (26, 38, 106) according to the device in claims 1-8 or the method according to claim 9, in a welding process.