Electricity: motive power systems – Positional servo systems
Patent
1993-11-22
1995-10-03
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
31856822, 318625, 318636, G05B 2102, G05B 1923
Patent
active
054554950
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control device intended for servocontrolling one or more objects to given positions. These devices are generally used in robotics. They may be involved, for example, in controlling motor shafts. This is the example which will be taken into consideration in what follows. It should, however, be noted that the control device according to the invention applies to the position servocontrol of any object.
2. Description of the Related Art
A conventional device for motor shaft control comprises a servocontrol of position and a servocontrol of speed of the motor shaft.
The speed servocontrol controls the motor shaft as long as the distance separating the actual position of the said shaft from the final position which the latter is to attain is greater than a given value. When this distance attains the said value, the position servocontrol comes in.
There is therefore a switching between the two types of servocontrol. This switching has disadvantages due to the instability inherent in this transition.
The existence of these two types of servocontrol and of the transition which links them requires circuits and algorithms of great complexity, leading to computation times which are often very lengthy.
SUMMARY OF THE INVENTION
In order to eliminate these disadvantages, the Applicant has designed a device enabling the position discrepancy to be servocontrolled with a single law, thereby allowing elimination of the switching between the two types of servocontrol. Through the servocontrol a non-linear relation is imposed between the position discrepancy and the action of the motor. There is then continuity in the decision making enabling the device to attain the desired objective. Although part of the control device is hardware-based, it is essentially software-based and therefore uses a microprocessor. Whether the algorithm used be a position and speed monitoring algorithm, as in the conventional devices, or an algorithm associated with a single law as mentioned above, the devices according to the prior art process the signals received in the same way without taking their frequency into account.
The customary correcting systems use the mathematical operation commonly called the "z transform". As is known by those skilled in the art, these systems perform a sampling at one frequency. The low frequencies of the signal studied are then processed at the same rate as the high frequencies.
This results in a loss of time at microprocessor level, this preventing, as a consequence, the control of several motor shafts in parallel with the aid of the same microprocessor, unless there is a loss in response time of the control device or unless a microprocessor with very high clock frequency, which is hence expensive, is employed.
The present invention does not have this disadvantage.
The subject of this invention is a control device intended for servocontrolling an object to a given position, the device comprising a forward/backward counting device enabling an absolute address in binary code to be provided from the indication of position of the object, a microprocessor enabling a signal for correcting the position of the object to be generated with the aid of a servocontrol algorithm, the algorithm making it possible to carry out a sequence of mathematical operations from the absolute address, in particular comparison of the address with an external set-point representing the given position so as to generate a position discrepancy signal, computation of a law providing a position signal deduced from the position discrepancy, differentiation of the position discrepancy followed by multiplication of the result of the differentiation, integration of the position discrepancy, addition of the results of the operations for computing the law, for multiplication arising from the differentiation and for integration, a device consisting of a digital/analog converter and an amplifier, and a motor controlled by the amplifier, the assembly being looped in
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patent: 3578957 (1971-05-01), Gatlin
patent: 4577271 (1986-03-01), Jones et al.
patent: 4794313 (1988-12-01), Ohmen
patent: 4893068 (1990-01-01), Evans
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patent: 5063335 (1991-11-01), Baechtel et al.
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Patent Abstracts Of Japan, vol. 12, No. 411 (p-779) 31 Oct. 1988, & JP, A, 63,148,309 (Yokogawa Electric Corp) 21 Jun. 1988, voir abrege.
Art Tech Gigadisc "ATG"
Ro Bentsu
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