Electricity: motive power systems – Plural diverse motor controls – Running-speed control
Patent
1997-06-27
1998-12-29
Ro, Bentsu
Electricity: motive power systems
Plural diverse motor controls
Running-speed control
31856818, 318630, G05B 19416
Patent
active
058545441
DESCRIPTION:
BRIEF SUMMARY
This application is a National Stage of International Application PCT/EP95/03973 under 35 USC .sctn.371, filed Oct. 9, 1995.
FIELD OF THE INVENTION
The present invention relates to a method for controlling the speed of electric drives, in particular of machine tools or robots.
BACKGROUND INFORMATION
Modern drives, for example for use in machine tools or robots, are distinguished by high dynamics. The values for speed control, which are prescribed on the desired value side by the industrial controllers and frequently also include jumps in acceleration, therefore produce acceleration shocks to the machine. If a gear mechanism which is connected to such a machine has so-called slack effects, i.e. play between, for example, gearwheels, has come about, for example in the course of the operating time, the gear mechanism is suddenly relieved of load. Owing to the hysteresis-like profile of such a slide drive with slack, considerable oscillations on the machine may be brought about. Such oscillations are, however, undesired since, for example in the case of grinding, they lead to degradation of the surface quality or, in the case of laser cutting, they lead to degraded dimensional accuracy. For this reason, efforts are made to design the speed control of such a modern drive in such a way that jolts, deriving from acceleration over time, are limited as far as possible.
It is known that, in order to fulfill this requirement, in conventional methods for controlling the speed in machine tool controllers either speed-independent acceleration limitation is taken into account, which limits the possible axle acceleration independently of the respective rotational speed of the electric drive or the speed values are filtered by means of a smoothing time constant on the path and an additional smoothing means in the drive as described in European Patent Application No. 0 477 412 and U.S. Pat. No. 4,603,286.
These two conventional methods which are used as standard ways of controlling the speed in machine tool controllers have, however, the disadvantage that, on the one hand, the axial smoothing causes speed-dependant and acceleration-dependant contouring errors and thus degrades the contouring accuracy. The only remaining way of preventing such a contouring error is to reduce the path acceleration limit in order to reduce shock loads and jolt loads. However, on the other hand, a consequence of this is that the efficiency of the machine is not completely utilized.
SUMMARY OF THE INVENTION
The present invention is therefore based on the object of designing a method for controlling speed, in such a way that impacts to the gear mechanism and machine can be avoided and the excitation of the machine which produces oscillations is reduced in an adjustable manner, and, at the same time, however, the efficiency of the machine can, if possible, be utilized to the greatest possible extent. Moreover, the effect of such jolt limitation is to be that slack effects do not, if possible, occur or already existing slack effects are not amplified further in the course of operation.
According to the present invention, this object is achieved by means of the following features: acceleration limit is approached in a plurality of steps whose number depends on the utilization of a maximum permissible jolt, and is thus kept at a constantly high value irrespective of the resulting overall acceleration change, prescribed over time, in which case, in a desired speed approach phase, the machine is adjusted to the desired speed as quickly as possible with optimum utilization of the maximum permissible acceleration and of the maximum permissible jolt, but with as few small jolt changes as possible, upper-limit which is to be maintained as long as possible, look-ahead manner in a target approach phase, acceleration, if there is an existing travel margin reducing it to the desired speed and, finally, braking to target speed at the latest possible time with the smallest possible continuous jolt changes.
A first, particularly advantageous refinement o
REFERENCES:
patent: 4603286 (1986-07-01), Sakano
patent: 5070287 (1991-12-01), Boehm
patent: 5510996 (1996-04-01), Kuhn et al.
patent: 5652490 (1997-07-01), Bradshaw et al.
Speth Wolfgang
Westermeyer Wilhelm
Ro Bentsu
Siemens Aktiengesellschaft
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