GB2143798A

GB2143798A - Improvements in and relating to automatic assembly process equipment

Info

Publication number: GB2143798A
Application number: GB08231902A
Authority: GB
Inventors: Robin Desmond Radcliff Andrews
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-11-09
Filing date: 1982-11-09
Publication date: 1985-02-20

Abstract

A parts assembly gripper 2 for automatic assembly is mounted by suspension means 3 from a transfer apparatus 1, so that the spherical surface 7 at its remote end is in substantially vertical relation with the suspension 3, and automatically adjusts itself by gravity to maintain the alignment. In order to facilitate assembly of a transported item to its container 5, fixed guide tooling 4 is provided which has accurate alignment with the location of the container. During assembly, when the suspension means 3 is lowered, there may be misalignment with the container. The conical guide surface 9 cooperates with the spherical surface to align the item so that as the suspension means is lowered, the spherical surface enters the location bore 8, thereby ensuring close alignment with the container and permitting assembly. The suspension means possesses sufficient resilience to enable the gripper to align itself to the guide tooling as it is lowered during assembly. <IMAGE>

Description

SPECIFICATION Improvements in and relating to automatic assembly process equipment Due to rising labour costs within the developed world, there is a strong trend present in industry for the reduction in labour use in manufacturing, by the installation of man-replacing machines.

Typically this trend is visible in all forms of industry, both high volume manufacturing for the automation of monotonous tasks (e.g. assembly) and in tasks which a human finds tiring (e.g. heavy parts transfers) or hazardous (e.g. unloading steel furnaces, paint spraying, or radioactive isotope handling).

This invention relates to improvements in current methods of automation of manufacturing processes, using for example robotic manipulators, with particular relevance (though not exciusively) to assembly and similar tasks.

Commonly, assembly is found to consist of insertion of parts such as bearings, pistons, seals, items for packaging, etc, into housings, bodies or containers. Because of the need for location, once positioned, often the axis of insertion takes place in the vertical direction.

In consideration of robotic manipulator devices, such as the 'pick and place' type in the simple case, it is obvious that the high cost usually found is related to the number of moveable 'joints', whether articulated, sliding linear, or revolute. Of particular complexity is the design and manufactore of 'wrist' mechanisms, that part of the manipulator nearest to the end-effector or 'gripper' which performs the actual task.

Besides the need for light weight owing to the large mounting distance (when compared with other 'joints'), the wrist usually has to perform rotational and/or reciprocating motions in several axis directions. Thus the wrist axes are commonly expensive to produce.

It is an object of this invention to simplify the design, and hence reduce cost, of these manipulators by means of an innovation in 'gripper' design. A property of a suspended gravitational pendulum is that the force of gravity acts to maintain the axis of the pendulum aligned with the vertical direction.

According to the invention, if a pendulum is suspended with its mounting gimbals attached to the end of the manipulator for example, it will hang vertically below the gimbals with high degree of positional reliability. Gripper means to pick or place parts may be magnetic, suction, or other convenient method, and mounted on the pendulum.

As the point of suspension of the pendulum moves in space, the gripper means (at the remote end of the pendulum) will follow, subject only to the acceleration (f) of the suspension point. The deviation angle for a simple pendulum is related to the ratio f/g, where g is acceleration due to gravity. However, as small assemblies often involve small distances in parts transfers, to be performed in seconds rather than fractions of seconds, the values off can be restricted in practice to the range r10 x g to 100 x g.

10 100 However, not all robotic movements are smooth, and occasionally high accelerations or decelerations can occur in practice. Unfortunately the undamped motion of a simple pendulum would resuit in a number of 'overshoots', where the pendulum axis oscillates about the mean deviation position during acceleration, or about the vertical axis once steady conditions pertain. Such a situation makes any assembly operation difficult to perform.

In order to overcome this problem, it is another object of this invention to mount a rotor on the pendulum, not necessarily with their axes coincident. Conveniently the rotor axis does coincide with the pendulum axis, and the rotor is arranged to rotate at high speed, driven by electrical, pneumatic or other convenient means. It is a well understood principle that a spinning rotor defines an axis of angular momentum, which then exerts a force on any system to prevent rotation of this axis. Thus an angular damping torque is produced, proportional to the rate at which the deviation angle is changing.

For small deviation angles, a, the system can be analysed by gyroscopic analysis, with the following result: 2f pt a = -Sin (2) g 2 where t is the time during which acceleration f is present, and p is a constant = wl/n. In this formula, w is the weight of the pendulum, I is the distance below suspension point of the centre of gravity, and n is the rotor angular momentum.

Accordingly a low value of wl, combined with high n, restricts deviation angle to a value less than f/g.

Furthermore, in light assembly, time t can be held to a fraction of a second.

Thus the gripper means can be designed to follow accurately the motion of the pendulum suspension point, in the horizontal plane, whilst maintaining a fixed distance vertically below.

It can be seen that the invention substantially eliminates the need for a complex wrist joint. In its simplest form, the manipulator specification can consist of a single joint, which performs the horizontal translation from a 'pick' point to a 'place' point for example.

Vertical movement of the gripper can be arranged by a simple rotation of the manipulator boom, for example, from one 'stop' to another in similar manner to conventional automatic assembly escapements.

In common assembly situations, the accurancy and repeatability of robotic manipulators has to be very high, often 0.05 mm, owing to low clearances between mating parts, tight fits of products in containers etc.

It is another object of this invention to greatly simplify the unit cost of the manipulator, and to enhance its reliability by so doing. In applications where unit breakdown is most undesirable, e.g. high production rates where 'down time' is not available, or in hazardous environments (such as radioactive isotope handling) where maintenance is difficult, the latter factor may be of greater importance.

Accordingly use is made of the pendulum to ease significantly the accuracy, or resolution, of the manipulator, by a complete order of magnitude to perhaps 1 mm. A suitably shaped fixed tooling guide, can be mounted in accurate close vertical alignment with a pick or place position, such as a container for example.

In operation, the gripper means may be arranged to pick up a product, for example (for subsequent placement in the container). The manipulator is programmed to move to a position close to the container vertical axis, such that the pendulum suspension point is for example within 1 mm of that axis. As the suspension point is lowered (for product insertion) the gripper means may be off centre from the container.

However, if the gripper is suitably shaped, the fixed guide will align the gripper end (by rotation of pendulum about its suspension) into the correct position relative to the container. Provided the length of the pendulum L is sufficiently great, and the position resolution error e is sufficiently small, there will be many application in industry where the misalignment angle e/L is acceptable (for example, with sufficient clearance of product within its container).

By way of example only, the attached drawing illustrates a manipulator system for handling radioactive isotope packaging. Due to the radioactivity hazard, the operations are carried out within lead-lined booths where the containerisation point may be 24 inches from the front wall. At the front wall is an inspection window, and it houses the mounting for a two axis manipulator.

In this example, the plane of manipulator movement is substantially horizontal: small vertical motion is obtained by rotation of the boom about its horizontal axis.

Seen in the drawing is the pendulum mounted gripper, utilising a Hooke's joint as the suspension universal joint. The rotor is mounted beneath the Hooke's joint, and at the base of the pendulum is a vacuum gripper tool.

Drawn adjacent to the gripper is the tooling guide, shown aligning the gripper so that the product may be inserted in line with its container. In this way a positional offset of the manipulator can be accommodated, thereby reducing position resolution, and a simple two axis robotic manipulator can be employed.

Wrist axis motions are completely avoided, with consequent reduction in unit cost, and increase in 'service' reliability, a most important factor in the radioactivity environment. The joints are powered, in this example, by motors mounted outside the lead cabinet, thereby further reducing weight of the manipulator, and providing ready access for maintenance. Transmission of motor power to each joint may be effected by toothed belts or tape, and if feedback is required for servo control, potentiometers can be installed at each joint to register anguler position.

As a further refinement, the control of the manipulator can be effected manually using a teach pendant. In this mode, the motion programme is taught by making the manipulator move through a required path cycle. Since visibility is so poor, a system is desired which an operator finds easy to use.

According to the invention, the teach pendant controller is provided with a joystick, for example, a lever spring-loaded to a central position where no robot movement takes place. Motion of the joystick in one axis controls movement of the manipulator in one horizontal axis, whilst motion perpendicular to this is achieved by movement of the joystick in a similar fashion. A combination of movements results in similar displacement of the manipulator gripper.

The proportion of joystick movement determines speed of manipulator motion. Thus releasing joystick causing movement to cease, since the desired velocity falls to zero, in its position pertaining at point of release. The manipulator can be 'inched' accurately by eye to a chosen position before recording the point in computer memory, for programme compilation. The tiring operation of remote handling tongs is eliminated in the invention.

The objects of this invention are embodied in the attached drawing.

CLAIMS (Filed on 9.12.83) 1. A device for the holding and manipulation of items for assembly, comprising a holding member supported by a manipulative apparatus, and resilient mounting means affording sufficient flexure between them so that the holding member is enabled to adjust its position by gravity, characterised by a substantial vertical alignment between the centre of the mounting means and the centre of gravity of the holding member.

2. A device according to Claim 1, wherein a part of the holding member sufficiently remote from the mounting means to permit flexure relative to the manipulative apparatus is appropriately formed to act as a guide, and acts in cooperation with a fixed guide suitably shaped to move the holding member to a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. example, from one 'stop' to another in similar manner to conventional automatic assembly escapements. In common assembly situations, the accurancy and repeatability of robotic manipulators has to be very high, often 0.05 mm, owing to low clearances between mating parts, tight fits of products in containers etc. It is another object of this invention to greatly simplify the unit cost of the manipulator, and to enhance its reliability by so doing. In applications where unit breakdown is most undesirable, e.g. high production rates where 'down time' is not available, or in hazardous environments (such as radioactive isotope handling) where maintenance is difficult, the latter factor may be of greater importance. Accordingly use is made of the pendulum to ease significantly the accuracy, or resolution, of the manipulator, by a complete order of magnitude to perhaps 1 mm. A suitably shaped fixed tooling guide, can be mounted in accurate close vertical alignment with a pick or place position, such as a container for example. In operation, the gripper means may be arranged to pick up a product, for example (for subsequent placement in the container). The manipulator is programmed to move to a position close to the container vertical axis, such that the pendulum suspension point is for example within 1 mm of that axis. As the suspension point is lowered (for product insertion) the gripper means may be off centre from the container. However, if the gripper is suitably shaped, the fixed guide will align the gripper end (by rotation of pendulum about its suspension) into the correct position relative to the container. Provided the length of the pendulum L is sufficiently great, and the position resolution error e is sufficiently small, there will be many application in industry where the misalignment angle e/L is acceptable (for example, with sufficient clearance of product within its container). By way of example only, the attached drawing illustrates a manipulator system for handling radioactive isotope packaging. Due to the radioactivity hazard, the operations are carried out within lead-lined booths where the containerisation point may be 24 inches from the front wall. At the front wall is an inspection window, and it houses the mounting for a two axis manipulator. In this example, the plane of manipulator movement is substantially horizontal: small vertical motion is obtained by rotation of the boom about its horizontal axis. Seen in the drawing is the pendulum mounted gripper, utilising a Hooke's joint as the suspension universal joint. The rotor is mounted beneath the Hooke's joint, and at the base of the pendulum is a vacuum gripper tool. Drawn adjacent to the gripper is the tooling guide, shown aligning the gripper so that the product may be inserted in line with its container. In this way a positional offset of the manipulator can be accommodated, thereby reducing position resolution, and a simple two axis robotic manipulator can be employed. Wrist axis motions are completely avoided, with consequent reduction in unit cost, and increase in 'service' reliability, a most important factor in the radioactivity environment. The joints are powered, in this example, by motors mounted outside the lead cabinet, thereby further reducing weight of the manipulator, and providing ready access for maintenance. Transmission of motor power to each joint may be effected by toothed belts or tape, and if feedback is required for servo control, potentiometers can be installed at each joint to register anguler position. As a further refinement, the control of the manipulator can be effected manually using a teach pendant. In this mode, the motion programme is taught by making the manipulator move through a required path cycle. Since visibility is so poor, a system is desired which an operator finds easy to use. According to the invention, the teach pendant controller is provided with a joystick, for example, a lever spring-loaded to a central position where no robot movement takes place. Motion of the joystick in one axis controls movement of the manipulator in one horizontal axis, whilst motion perpendicular to this is achieved by movement of the joystick in a similar fashion. A combination of movements results in similar displacement of the manipulator gripper. The proportion of joystick movement determines speed of manipulator motion. Thus releasing joystick causing movement to cease, since the desired velocity falls to zero, in its position pertaining at point of release. The manipulator can be 'inched' accurately by eye to a chosen position before recording the point in computer memory, for programme compilation. The tiring operation of remote handling tongs is eliminated in the invention. The objects of this invention are embodied in the attached drawing. CLAIMS (Filed on 9.12.83)

1. A device for the holding and manipulation of items for assembly, comprising a holding member supported by a manipulative apparatus, and resilient mounting means affording sufficient flexure between them so that the holding member is enabled to adjust its position by gravity, characterised by a substantial vertical alignment between the centre of the mounting means and the centre of gravity of the holding member.

predetermined position corresponding to the location of the fixed guide.

3. A device as claimed in Claims 1 or 2, wherein the holding member guide surface is further shaped to provide close alignment between a manipulated component and the guide surface of the holding member.

4. A device according to any preceding Claims whereby the fixed guide is further formed to afford location for the outer container of any assembly, characterised by close alignment between the fixed guide and the container.

5. A device according to any preceding Claims, wherein the remote end of the holding member is formed as part of a spherical surface.

6. A device according to any preceding Claims, wherein the fixed guide comprises a cylindrical location bore which cooperates with the spherical guide surface of the holding member, and a conical surface which acts to guide the holding member into close alignment with the location bore.

7. A device as claimed in any of the preceding Claims, wherein the mounting means comprises a universal joint of the Hooke type.

8. A device, as claimed in any of the preceding Claims, in which the means of holding components comprises a vacuum created between the component and the holding member.

9. A device as claimed in any of the preceding Claims, wherein the holding member is arranged to support a rotor, characterised by close alignment between its axis of rotation and the axis obtained by joining the centre of flexure of the mounting means to the centre of gravity of the holding member.