EP1523398A1

EP1523398A1 - A robot wrist and a method of constructing the same including a tilt housing

Info

Publication number: EP1523398A1
Application number: EP03741738A
Authority: EP
Inventors: Daniel LUNDBÄCK; Roswitha STRÖM; Ove Kullborg
Original assignee: Asea Brown Boveri AB; ABB AB
Current assignee: ABB AB
Priority date: 2002-07-18
Filing date: 2003-07-04
Publication date: 2005-04-20
Also published as: SE0202264D0; JP2006500229A; WO2004009302A1; AU2003281508A1

Abstract

Robot wrist (7), for a robot arm (5), which includes a tilt housing (8) that is arranged to rotate about a first axis (C) and which comprises a first motor (10) and a first gear assembly (11) which cause the tilt housing (8) to rotate about said first axis (C), where the output shaft (15) of the first motor (10) is arranged to be coaxial with said first axis (C).

Description

A ROBOT WRIST AND A METHOD OF CONSTRUCTING THE SAME INCLUDING A TILT HOUSING.

TECHNICAL FIELD

The present invention relates to an industrial robot and more particularly to a robot wrist, for a robot arm, which includes a tilt housing that is arranged to rotate about a first axis and which comprises a first motor and a first gear assembly which cause the tilt housing to rotate about said first axis. The present invention concerns the arrangement of the motor and the gear assembly inside the robot wrist and also relates to a method for constructing a robot wrist.

BACKGROUND OF THE INVENTION

Many industrial robots comprise a robot arm that is arranged to rotate about an axis that coincides with the longitudinal centre line of the robot arm. The robot arm supports a robot wrist at its distal end, which includes a tilt housing. The tilt housing rotates about a first axis that is at an angle to the longitudinal centre line of the robot arm. The tilt housing is often equipped with a tool support that is arranged to rotate about a second axis that is at an angle in relation to first axis. A robot tool, or other desired attachment is mounted on the tool support.

Control of the rotational movements of the robot arm and tilt housing is achieved by electric motors that are usually mounted inside the robot arm or in the support carriage of the robot wrist. It is known that the control of the rotational movements of the tool support can be achieved by an electric motor that is mounted inside the tilt housing. Transmission means such as gears, drive chains or belts transmit the rotation of the motor and actuate the desired rotation about each axis of rotation. Industrial robots often have to operate in and/or access small or confined spaces. The space available for a robot wrist is therefore only available to a limited extent. For this reason the motor controlling the rotation of the tilt housing is mounted at the rear of the robot arm. Transmission means, such as a belt drive, are then arranged along the robot arm from the motor to the robot wrist. Such an arrangement causes operating play between the various parts as, for example, there usually is creep or slip in a belt drive.

US4527945 discloses a robot wrist, for a robot arm, which includes a tilt housing that rotates about an axis that is perpendicular to the longitudinal axis of the robot arm. The robot wrist contains a motor that causes the tilt housing to rotate and a reduction gear assembly that comprises a first reduction stage, consisting of a gear train with parallel axes, followed by a second reduction stage, consisting of a differential reduction unit.

The motor's output shaft points outwards from the longitudinal centre axis of the tilt housing in a direction parallel to the axis around which the tilt housing rotates and it bears an output pinion constituting the first element of the first stage of reduction. Said output pinion cooperates with an intermediate pinion, the axis of which is parallel to the motor's output shaft. The intermediate pinion engages a driven pinion the axis of which is also parallel to the motor's output shaft. The driven pinion constitutes the input of the second stage of reduction that is mounted on the axis of rotation of the tilt housing.

The pinions of the first stage of reduction transmit motion between three parallel shafts from the motor to the second stage of reduction. Each shaft gives rise to friction losses. The length of the robot wrist needs to be sufficient to house the motor and the first and second reduction stages, which are located side by side. The breadth of the robot wrist has to be sufficient to accommodate the motor with its protruding output shaft. Alternatively the motor is arranged so that its output shaft points in a direction perpendicular to the axis around which the tilt rotates. A bevel gear is then needed to change the direction of the motor rotation by 90°.

In summary there is a need in the industry to produce a compact and lightweight robot wrist that is easy to service and repair.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a compact and lightweight robot wrist for a robot arm. This and other objects of the invention are achieved by producing a robot wrist, for a robot arm, which includes a tilt housing that is arranged to rotate about a first axis and which comprises a first motor and a first gear assembly which cause the tilt housing to rotate about said first axis as described in the characterizing portion of claim 1 , namely where the output shaft of the first motor is arranged to be coaxial with said first axis.

According to a preferred embodiment of the invention the output shaft of the first motor is arranged to directly drive the gear wheel constituting the input of the first gear assembly. By 'directly' it is meant that transmission means, such as a bevel gear, between the first motor and the first gear assembly are not required thus decreasing the size and weight of the robot wrist. The maintenance/repair time and complexity of this drive unit are thereby reduced as a consequence of there being fewer parts to service/repair, which in turn leads to an increase in productivity and a decrease in production costs.

According to a preferred embodiment of the invention the robot wrist further comprises a second motor and a second gear assembly which drive a tool support that is arranged to be rotatable about a second axis, that is at an angle in relation to the first axis. The output shaft of the second motor is arranged to directly drive a gear wheel constituting the input of a second gear assembly. In a further preferred embodiment the output shaft of the second motor is arranged to be coaxial with said second axis.

In order to accommodate two motors in the robot wrist in the minimum of space, the second motor is placed adjacent to the output shaft of the first motor i.e. between the first motor and the first gear assembly. According to an alternative preferred embodiment the second motor is placed adjacent to the mantle of the first motor. If this alternative preferred embodiment is chosen the robot wrist's breadth can be decreased although its length becomes slightly greater than if the second motor is placed adjacent to the output shaft of the first motor.

According to further preferred embodiment of the invention the first motor is contained entirely within the tilt housing rather than being mounted on the support carriage of the robot wrist. According to another preferred embodiment of the invention the first gear assembly is contained entirely within the tilt housing rather than being mounted on the support carriage of the robot wrist. An advantage of such arrangements is that the tilt housing can be rapidly and easily removed from the robot arm and replaced in its entirety. According to a yet further preferred embodiment of the invention at least one motor is a compact servomotor.

The invention also relates to a method of constructing a robot wrist, for a robot arm, which includes a tilt housing that is arranged to rotate about a first axis and which comprises a first motor and a first gear assembly which cause the tilt housing to rotate about said first axis. The method comprises the steps of mounting a first gear assembly inside the robot wrist so that the output shaft of the gear assembly is coaxial to the first axis and mounting the first motor with its output shaft coaxial with the first axis and connecting the first motor's output shaft with the gear wheel constituting the input of the first gear assembly.

According to the invention the robot wrist as described in any of the preferred embodiments constitutes part of an industrial robot intended for use in any application such as welding, assembly work, spraying, painting, machine tending, lifting, picking, packing, cutting, grinding, polishing or for medical applications. The invention is particularly suitable for applications where a robot arm or robot wrist must be lightweight and able to operate in small or confined spaces.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described by way of example and with reference to the accompanying drawing in which:

figure 1 exemplifies a conventional six-axis industrial robot,

figure 2 shows a robot wrist according to one preferred embodiment of the present invention, and

figure 3 depicts a robot wrist according to a second preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a conventional six-axis industrial robot. The robot has a stand 1 that is rotatably mounted on a base 2, which enables it to rotate about vertical axis A. A lower robot arm 3 is pivotably mounted to allow rotation about axis 4. The lower robot arm 3 supports the robot's upper arm 5. The upper arm is pivotly mounted to allow rotation about axis 6. The upper arm 5 is rotatable about axis B that coincides with the longitudinal axis of the upper arm. The upper arm is joumalled in a bearing housing 5a and a motor 5b, that is located adjacent to the bearing housing, actuates the rotation of the upper arm 5.

The upper arm supports a robot wrist 7 at its distal end, which includes a tilt housing 8 that is rotatable around an axis C that is perpendicular to the longitudinal axis B of the upper arm 5. The tilt housing contains a drive unit that drives a tool support 9. The tool support 9 rotates about axis D that is perpendicular to axis C. A robot tool or other desired attachment is mounted on the tool support 9.

The industrial robot of the present invention is not restricted to six-axis industrial robots like the one schematically illustrated in figure 1 but is intended for use in any type of industrial robot such as a vertical, horizontal or gantry robot.

Figure 2 shows an enlarged view of the robot wrist 7 that has a support carriage comprising two fork elements between which a tilt housing 8 is pivotably mounted. The tilt housing is equipped with a rotatable tool support 9. The robot wrist comprises a first motor 10, such as a compact servomotor and a first gear assembly 11 such as a coaxial differential reduction unit that makes it possible to achieve significant reduction ratios using a very compact, lightweight mechanical unit. The first motor and the first gear assembly cause the tilt housing to rotate about an axis C that is perpendicular to the longitudinal axis of the -robot arm 5.

The robot wrist 7 also comprises a second motor 12, whose output shaft 13 drives a second gear assembly 14 that in turn actuates the tool support 9 that is arranged to be rotatable about an axis D that is perpendicular axis

C. Said first motor (10) is placed transversely, so that its output shaft (15) is coaxial with axis C and is arranged to directly drive the gear wheel constituting the input of the first gear assembly 11. The second motor 12 is positioned adjacently to the output shaft 15 of the first motor 10 in order to minimize the length of the tilt housing. The servomotors are provided with devices used to correct the performance of the motors by means of an error-sensing feedback (not shown).

Figure 3 depicts a robot wrist where the second motor 12 is positioned adjacent to the mantle of the first motor 10. This arrangement produces a more narrow robot wrist 7 than in the embodiment shown in figure 2 however the length of the tilt housing 8 is thereby slightly increased. The spatial dimensions of the robot wrist can be optimized as desired for a particular application. In this figure the first motor 10 is contained entirely within the tilt housing 8 whereas in the previous figure the first motor is mounted on one of the fork elements and extends into the tilt housing. In both figures (2 and 3) the first gear assembly is mounted on one of the fork elements and extends into the tilt housing.

While only certain preferred features of the present invention have been illustrated and described, many modifications and changes will be apparent to those skilled in the art. It is therefore to be understood that all such modifications and changes of the present invention fall within the scope of the claims.

For example a person skilled in the art will realize that the first and second motors can be placed in many more configurations with respect to each other inside the robot wrist and/or the tilt housing in addition to the two arrangements that have been shown by way of example, the configuration that is chosen depending on the requirements of the robot user.

Claims

1. Robot wrist (7), for a robot arm (5), which includes a tilt housing (8) that is arranged to rotate about a first axis (C) and which comprises a first motor (10) and a first gear assembly (11) which cause the tilt housing (8) to rotate about said first axis (C), characterized in that the output shaft (15) of the first motor (10) is arranged to be coaxial with said first axis (C).

2. Robot wrist according to claim 1 , characterized in that the output shaft of the first motor is arranged to directly drive the gear wheel constituting the input of the first gear assembly (11).

3. Robot wrist according to claims 1 or 2, characterized in that the robot wrist further comprises a second motor (12) and a second gear assembly (14) which drive a tool support (9) that is arranged to be rotatable about a second axis (D) that is at an angle in relation to the first axis (C) where the output shaft (13) of the second motor (12) is arranged to directly drive a gear wheel constituting the input of a second gear assembly (14)

4. A robot wrist according to claim 3, characterized in that the output shaft (13) of the second motor (12) is arranged to be coaxial with said second axis (D).

5. Robot wrist according to claims 3 or 4, characterized in that the second motor (12) is placed adjacent to the output shaft (15) of the first motor (10).

6. Robot wrist according to claims 3 or 4, characterized in that the second motor ( 2) is placed adjacent to the mantle of the first motor (10).

7. Robot wrist according to any preceding claims, characterized in that the first motor (10) is contained entirely within the tilt housing (8).

8. Robot wrist according to any preceding claims, characterized in that the first gear assembly (11) is contained entirely within the tilt housing

(8).

9. Robot wrist according to any preceding claims, characterized in that at least one motor (10, 12) is a compact servomotor.

10. Robot arm characterized in that it comprises a robot wrist (7) according to any of the preceding claims.

1 1 . Industrial robot characterized in that it comprises a robot wrist (7) according to any of claims 1 -9.

12. Method of constructing a robot wrist (7), for a robot arm (5), which includes a tilt housing (8) that is arranged to rotate about a first axis (C) and which comprises a first motor (10) and a first gear assembly (1 1 ) which cause the tilt housing (8) to rotate about said first axis (C), characterized in that it comprises mounting a first gear assembly (1 1 ) inside the robot wrist so that the output shaft of the gear assembly is coaxial to the first axis (C), mounting the first motor (10) with its output shaft (15) coaxial with the first axis (C), and connecting the first motor's output shaft (15) with the gear wheel constituting the input of the first gear assembly (11 ).

13. Method according to claim 1 1 , characterized in that the first motor (10) is housed entirely within the tilt housing (8).

14. Method according to claims 12 or 13, characterized in that the first gear assembly (11) is housed entirely within the tilt housing (8).

15. Method according to any of claims 12-14, characterized in that a second motor (12) is mounted inside the robot wrist adjacent to the output shaft (15) or the mantle of the first motor (10).

16. Use of a robot wrist according to any of claims 1-9, a robot arm according to claim 10, an industrial robot according to claim 11 in any application where a lightweight, compact robot wrist (7) is required.