Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1989-12-19
1991-10-01
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318566, 31856811, 901 21, 901 28, 901 29, B66F 900
Patent
active
050536877
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an articulated device of the type comprising two plates interconnected by articulated segments shaped to form a closed latticework structure together with a control assembly for controlling the relative positions of the two plates.
In the prior art, such a device is referred to as a "parallel manipulator" and it generally possesses six segments of variable length articulated on the plates via universal joints, together with a control assembly which enables up to six degrees of freedom to be obtained for one plate relative to the other. The device is particularly suitable for use in robotics where it may constitute, for example, the end of a robot arm for insertion or assembly purposes, or it may constitute a structure fixed to a stationary platform for facing a robot arm. In this application the device constitutes a "left hand" for the robot facing it. In all cases, the device should enable complex tasks to be performed of fine assembly, precision machining, or contact monitoring of surfaces.
A device of this type may also be used in dynamic motion simulators, e.g. flight simulators or other vehicle control simulators.
French patent application number 83 12263 describes a device of this type which comprises two plates interconnected by six pneumatic actuators constituting actuators which are articulated both to the top plate and to the bottom plate, and which are controlled by electrically controlled valves. This type of manipulator has inherent natural elasticity due to the pneumatic actuators and it is most advantageous for robotics by virtue of its high position accuracy and of the ease with which force measurement may be integrated. However, such a device is relatively bulky and has relatively high mass and inertia in its moving parts, thereby limiting its speed of displacement. This considerable bulk is related to the presence of the actuators for driving the articulated segments and these also limit the working space of the device because of their diameter. Finally, the pneumatic actuators expend energy even when the top plate is not moving.
A document by Jean-Pierre Merlet entitled "Parallel Manipulator, Part 1: Theory, Design, Kinematics and Control", INRIA Research Report, No. 646, March 1987, and referred to herein as the Merlet Document describes a device which is more specifically intended to provide "left hand" functions for a robot. This device is likewise constituted by two plates interconnected by segments which are articulated both to the top plate and to the bottom plate. Each segment of this device is provided with a resilient member which enables the length of each segment to modify a little under the influence of forces exerted on the top plate. The geometry of the device can thus be slightly modified under the influence of applied forces and the system is said to exhibit "passive compliance". The top plate can be moved since it is possible to control the length of each of the segments to some extent. This function is obtained by having an electric actuator in each of the segments. However, such electric actuators suffer from the drawback of being long relative to the small amount of variation in length they offer. Thus, typically, for segment length variation of no more than 5 cm, the segment length is 50 cm, thus giving rise to an overall system height of about 50 cm. This characteristic thus imposes relatively large bulk. In addition, the mass of electric actuators commercially available at present leads to a device having a relatively high total mass, about 11 kg. This is incompatible with the loading capacities of the commoner robots, and this device therefore cannot be used as the end of a robot arm for insertion or assembly purposes, for example.
The present invention remedies these drawbacks by proposing a device which, in addition to providing high positioning accuracy and heavy nominal loading, also provides greatly reduced total bulk together with reduced mass and inertia of the moving parts.
Another object of the invention is to obtain segments of m
REFERENCES:
patent: 4300362 (1981-11-01), Lande et al.
patent: 4732525 (1988-03-01), Neuman
patent: 4765795 (1988-08-01), Rebman
patent: 4806068 (1989-02-01), Kohli et al.
patent: 4819496 (1989-04-01), Shelef
Inria Institut National de Recherche en Information et en Automo
Ip Paul
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