GB2133381A - Robot arm - Google Patents

Abstract

A robot arm of modular construction comprises a series of interconnected, interchangeable sections or modules each independently powered and independently controlled. The extension sections include at least three sections which are guided for linear movement, relative to the preceding section, in respective directions which are mutually orthogonal. <IMAGE>

Description

SPECIFICATION Remote controlled devices Field of Invention This invention concerns remotely controlled devices often referred to as robots by which functions may be performed such as mechanical handling, machining, working, assembling and other functions related to the manufacture or treatment of products.

Background to the Invention So-called robots or robotic arms have become common place in the manufacturing industry both in this country and abroad. At the heart of most such systems is the so-called arm which is an engineering equivalent of a human arm in that it includes various rigid sections joined by joints which allow a degree of hinging pivoting sliding or other movement between adjoining sections.

Devices are provided at the joints to produce movement of one section relative to another by pivoting or hinging or sliding and the power to the various drive devices is controlled so as to cause the various sections to move and articulate in a controlled manner. By anchoring one end of the arm assembly either on a platform or to a workbench or to the floor or ceiling or wall, so the remote or outboard end of the arm assembly can be made to move relative to the fixed end and clearly the number of positions to which the outboard end can be moved will be dictated to a large extent by the number of articulating sections.

Clearly for a complicated function in which a number of different degrees of movement are required to enable accurate and closely controlled movement of the outboard end of the arm to be performed, a large number of different articulating sections will be required and separate drives and controls therefor. On the other hand there are many applications where only a two or three section arm would be adequate to perform the specific task for which the arm is required and the powering and operation of ali sections of the multiple section arm would not be necessary.

Summary of the Invention According to the present invention there is provided a robotic structure comprising a support, a plurality of extension sections including three extension sections each guided for linear movement relative to the preceding sections, the three directions of linear movement being mutually orthogonal, each extension section being independently powered and independently controlled for causing movement relative to the section to which it is connected.

A tool or workpiece holder or the like can be attached to the outermost section.

A preferred structure includes at least one extension section which is idependently powered and controlled for rotary movement about an axis parallel to one of said directions of linear movement. Preferably also, an outermost extension section is pivotally mounted to the preceding section about an axis parallel to one of said directions of linear movement.

Thus, in a practical embodiment, a robotic structure comprises a support adapted to be secured to a floor or other horizontal surface, a first extension section linearly movable in one horizontal direction relative to said support, a second extension section linearly movable relative to the first section in a horizontal direction perpendicular to the first mentioned direction, a third extension section mounted for rotary movement about a vertical axis relative to the second section, a fourth extension section mounted for vertical linear movement relative to the third section, and a fifth extension section pivotally mounted on the fourth section, each extension section being independently powered and independently controlled for causing movement relative to the preceding section.In this embodiment, the support and fourth extension section may have toothed tracks for enabling linear movement of the following section, whilst the second extension section has guide rails and the third section is slidable therealong. The fifth extension section is preferably mounted on the fourth section for pivotal movement about a horizontal axis parallel to the direction of linear movement of the third section.

The present invention is thus based on a modular approach to robot arm construction as regards both power and controls for the arm sections.

Thus, what is important is that if the arm outlives its required primary function, it can be modified by the addition of new parts, replacement of existing parts or possibly removal or unwanted parts from the overall assembly so as to provide the hardware necessary to perform another function. It is then only necessary to reprogramme the control signals to the arm to allow it to perform the new function.

During use, wear and tear on the different parts of an arm can result in failure and breakdown and an arm constructed in accordance with the present invention can, of course, be repaired and recommissioned with a minimum of time and effort by relatively unskilled personnel since it is only necessary to disconnect the arm from its power source, unbolt the offending section or sections and replace with standard sections from a stock of spare parts to enable the arm to be recommissioned. The offending parts can then be serviced or sent away for repair etc., as required.

In some instances part of the arm may be required to operate in a hostile environment even though other parts of the arm are not so required.

According, therefore, to another feature of the invention, not only are exchangeable sections provided but the range of sections available preferably includes sections formed from materials compatible with different environments, fluid media and the like so as to allow an arm to be constructed from conventional parts for those sections of the arm which do not operate in the hostile environment and from special purpose parts (i.e. constructionally similar but formed from suitable materials or coated with suitable materials) to allow those sections of the arm which are to operate in a hostile environment to be capable of withstanding the hostile attack that would otherwise occur.

The robotic arm is preferably electrically driven.

Each section conveniently includes an electric motor, a gearbox, a brake for locking the section in position, and a resolver to produce feedback to a central controller. A d.c. power amplifier is preferably associated with the motor to control direction and velocity, the power amplifier receiving information from the controller via a digital to analogue converter.

Associated control components for each section, including the amplifier, the digital to analogue converter, servo and drive, are preferably also of modular nature, and can be incorporated into a suitable housing as appropriate, together with a central controller for controlling operation of a plurality of sections.

Structures of the invention are very versatile and adaptable and find application in many fields, for example integrated with existing machinery and tooling on an automobile production line, to be used, e.g. for spot welding.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of a robotic structure embodying the invention; Figure 2 is a block diagram illustrating the components of a single section or module; and Figure 3 is a block diagram illustrating the overail arrangement of modules and controller.

Detailed Description of Drawings The arrangement shown in Figure 1 comprises a support 60 adapted to be secured to the floor or other horizontal surface. Support 60 comprises a track for guiding horizontal linear movement in the direction of arrows 62 of section or module 64 mounted thereto. Module 64 in turn includes track members 66 for guiding horizontal linear movement in the direction of arrows 68 (at right angles to the direction of arrows 62) of a further section or module 70. Module 72 is mounted on module 70 for rotary movement in horizontal piane, as indicated by arrows 74. Module 72 in turn carries a vertical track for guiding vertical movement of further module 76, as indicated by arrows 78. A final module 80, incorporating welding equipment, is pivotally mounted to module 76 for movement as indicated by arrows 82.

Figure 2 illustrates the components of a typical individual section or module, such as those described above.

The illustrated module includes a printed electric circuit motor 86 and a gearbox 88 sized to suit the load capability of the particular motor shaft. The gearbox has a nominal reduction ratio of 160:1, although ratios in the range 256:1 and 100:1 are possible.

A resolver 90 is fitted to the motor shaft to provide feedback to a central controller (not shown) relating to the position of the motor shaft.

A d.c. power amplifier 92 is associated with the motor 86 to control the direction and velocity of the motor. The power amplifier is driven by the digital output of the control element via a digital to an alogue converter 94 with a resolution of 8 bits, thus providing 127 discrete velocities in each direction (7 bits for velocity and 1 bit for direction).

The control input to the power amplifier is in the range +10 volts.

The position of the module is determined from the resolver 90. The resolver provides an output which is fed to a resolver-to-digital converter (RDC) 96 of 8-bit resolution. The RDC output is further subdivided by an 8-bit counter 98 and the resultant 1 6 bits of information supplied to the controller to provide positional information relating to the module.

An electromagnetic brake (not shown) is also mounted on the motor shaft. The brake has to be energised to release the mechanism so that when the module is not moving, the whole structure is rendered solid.

The harmonic drive comprising gearbox 88 consists of three main components: wave generator, a flexispline and a circular spline.

The wave generator is a thin wall ballrace fitted onto an elliptical former. The flexispline fits over the wave generator and is elastically deformed as the wave generator turns. The circular spline is an internally toothed solid steel ring which engages the flexispline across the major axis of the wave generator. About 15% of the pivotal number of teeth are engaged and the two sets of gears are equally pitched.

There is, however, a difference of two teeth between the fiexispline and the circular spline so that each revolution of the wave generator will precess the engagement, producing a relative motion.

The output shaft of the gearbox is connected to the circular spline whiie the input shaft drives the wave generator. The result is a high efficiency torque converter -- as the wave generator drives the flexispline - and a high ratio gearset as the circular spline moves on just two teeth for every revolution of the wave generator.

As shown in Figure 3, a number of modules 100 (6 in the illustrated arrangement) are controlled by a single central controller 1 02. The controller is further linked to an operator display panel 104, a teaching aid 106 and a work monitoring system.

Claims (10)

1. A robotic structure comprising a support, a plurality of extension sections including three extension sections each guided for linear movement relative to the preceding section, the three directions of linear movement being mutually orthogonal, each extension section being independently powered and independently controlled for causing movement relative to the section to which it is connected.

2. A structure according to claim 1 , also including at least one extension section which is independently powered and controlled for rotary movement about an axis parallel to one of said directions of linear movement.

3. A structure according to claim 1 or claim 2, also including an outermost extension section pivotally mounted to the preceding section about an axis parallel to one of said directions of linear movement.

4. A structure according to claim 3, wherein said outermost extension section is a tool or workpiece carrying section.

5. A robotic structure comprising a support adapted to be secured to a floor or other horizontal surface, a first extension section linearly movable in one horizontal direction relative to said support, a second extension section linearly movable relative to the first section in a horizontal direction perpendicular to the first mentioned direction, a third extension section mounted for rotary movement about a vertical axis relative to the second section, a fourth extension section mounted for vertical linear movement relative to the third section, and a fifth extension section pivotally mounted on the fourth section, each extension section being independently powered and independently controlled for causing movement relative to the preceding section.

6. A structure according to claim 5, wherein the support and the fourth extension section have toothed tracks for enabling linear movement of the following section, whilst the second extension section has guide rails and a third section is slidable therealong.

7. A structure according to claim 5 or claim 6, wherein the fifth extension section is mounted on the fourth section for pivotal movement about a horizontal axis parallel to the direction of linear movement of the third section.

8. A structure according to any one of the preceding claims, wherein each section conveniently includes an electric motor, a gearbox, a brake for locking the section in position, and a resolver to provide feedback to a central controller.

9. A structure according to claim 8, wherein a d.c. power amplifier is associated with the motor to control direction and velocity, the power amplifier receiving information from the controller via a digital to analogue converter.

10. A robot structure substantially as herein described with reference to, and as shown in, the accompanying drawings.