Electricity: motive power systems – Positional servo systems – Pulse-width modulated power input to motor
Patent
1994-10-13
1998-05-05
Masih, Karen
Electricity: motive power systems
Positional servo systems
Pulse-width modulated power input to motor
318254, 318138, 318439, G05B 1128
Patent
active
057479569
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a method of controlling the rpm of a motor by utilizing an incremental indicator.
It is known to perform an adjustment of the most varied devices, for example in motor vehicles, by means of servomotors. These servomotors are frequently used in motor vehicles to improve comfort, for example, in seat or window adjustment and the like. As a rule, these adjustment motors are equipped with integrated motor electronics, or are controlled by central electronics. To achieve precise positioning of the systems driven with the servomotors, it is known to integrate an incremental indicator or sensor configured as a path indicator which permits the devices to be adjusted to be transferred into different positions by means of an operating element.
It is, however, disadvantageous that, because of a possible jerky actuation of the servomotor, the actual adjustment mechanism is exposed to extremely high mechanical stress, which can lead to premature wear of the mechanical parts. Moreover, each actuation of the servomotor is associated with a startup short-circuit current that puts extreme stress on the voltage source only present to a limited degree in a motor vehicle.
SUMMARY AND ADVANTAGES OF THE INVENTION
The object of the invention is to create a method of controlling the rpm of a motor of the generic type, with which method motor control with a reduced startup short-circuit current and a reduced starting torque is possible.
In accordance with the invention, the above object generally is accomplished by a method of setting the rpm of an electric motor, wherein a control signal, which is supplied to a power output stage that actuates the motor, is pulse-width modulated and the actual rpm of the electric motor is measured via a measuring device (incremental indicator), and wherein the actual rpm is compared to a predetermined reference rpm value, and, if the reference rpm is not reached, the pulse width of the control signal is changed, e.g., increased, until the reference rpm value is reached.
By means of pulse-width modulation, it is accomplished that the control signal, cooperating with the incremental indicator, or sensor (RPM) can perform rpm control of the motor without problems. Through the availability of a plurality of possible rpms, a reduced starting torque in particular is achieved in addition to the improvement in comfort by means of more precise positioning options of the device to be adjusted. Thus, a jerky stress on the mechanical parts which effect the adjustment is avoided.
Furthermore, it is possible to perform a so-called soft start or soft stop of the motor by means of the adjustment of a motor rpm that is reduced initially. It is advantageous that the startup short-circuit current stressing the voltage source can be reduced by a gradual running-up of the motor rpm, and, in addition, a vibration-free and thus noise-reducing level adjustment of mechanical parts up to the maximum stress range is possible.
In a further embodiment of the invention, it is provided that the motor rpm is monitored and compared to a reference value. At the slightest deviation, an adaptation of the motor rpm can take place by means of the pulse-width modulation of the control signal. With this it can be accomplished in an advantageous manner that, despite a possibly exceedingly low battery voltage or excessive stress, the motor rpm can be set at the minimum necessary to achieve a sufficient adjustment speed.
Further advantageous embodiments of the invention ensue from the measures outlined in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWING
The invention is described in detail below in embodiments shown in the associated drawings wherein:
FIG. 1 is a block circuit diagram of an apparatus for practicing the method according to the invention;
FIG. 2 is a logic flow diagram for the circuit of FIG. 1;
FIG. 3 shows a control signal characteristic in the example of a soft start; and
FIG. 4 a shows control signal characteristic in the example of a soft stop.
DETAILING DESCRIPT
REFERENCES:
patent: 4782272 (1988-11-01), Buckley et al.
patent: 5084658 (1992-01-01), Nielsen et al.
patent: 5089761 (1992-02-01), Nakazawa
patent: 5146145 (1992-09-01), Wood et al.
patent: 5341452 (1994-08-01), Ensor
patent: 5459386 (1995-10-01), Okachi et al.
Masih Karen
Robert & Bosch GmbH
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