Electricity: motor control systems – Open loop speed control system for dc motor with commutator
Reexamination Certificate
2002-09-27
2003-11-25
Nappi, Robert E. (Department: 2837)
Electricity: motor control systems
Open loop speed control system for dc motor with commutator
C388S829000, C388S811000, C318S254100, C318S132000, C318S434000, C318S599000, C318S805000, C318S811000
Reexamination Certificate
active
06654548
ABSTRACT:
The present disclosure relates to the subject matter disclosed in international application No. PCT/EP02/00965 of Jan. 30, 2002, which is incorporated herein by reference in its entirety and for all purposes.
BACKGROUND OF THE INVENTION
The invention relates to a method for control of the speed of rotation of a separately excited direct current motor for model vehicles, the speed of rotation of the motor being controlled by means of a pulse sequence, the motor being alternately supplied with a supply voltage during a switch-on period and disconnected from the supply voltage during a switch-off period, the duration of the switch-off period being dependent on the deviation of an actual value from a set value for the speed of rotation of the motor.
The invention also concerns a control unit for control of the speed of rotation of a separately excited direct current motor for model vehicles for carrying out the method comprising an on-off controller for control of a switch element for alternate switch-on and switch-off of the direct current motor, the controller providing a series of pulses.
The invention further relates to a decoder unit for electrical model vehicles, in particular for vehicles for a model railway, having a control unit of this kind, as well as to a model vehicle, above all a model railway vehicle, having a separately excited direct current motor and a control unit of this kind.
Drive of electrical model vehicles, in particular electrical model railway vehicles, is frequently effected by means of separately excited direct current motors. If the required running properties of the model vehicles are to be assured, the speed of rotation of the motors must be capable of being controlled in a stable manner over a wide range. For this purpose, on-off controllers are generally used, by means of which a pulse sequence is provided for control of a switch element by which the motor can be supplied with a supply voltage. The voltage supply is effected by this during a switch-on period corresponding to the pulse sequence. The switch-on period may be preset to be fixed. During a switch-off period of the pulse sequence, the supply voltage is disconnected from the motor. The duration of the switch-off period is dependent on the deviation of the actual value from the set value for the speed of rotation of the motor. The actual value is determined by measurement of the induction voltage present at the armature winding of the motor during the switch-off period. This induction voltage is frequently also called “counter-EMF” (electromotive force). The higher the speed of rotation of the motor, the greater the induction voltage. This induction voltage is compared with an adjustable set value by means of the on-off controller, and according to the deviation of the actual value from the set value of the induction voltage and therefore from the desired speed of rotation of the motor, the switch-off period of the pulse sequence is extended or shortened.
A control method of this kind enables reliable control of the speed of rotation, especially in the slow speed range of the model vehicle. The noise output, which is inherent to the control principle is however disadvantageous, especially for high-grade motors, for example motors having bell-shaped armatures, the noise output being developed by the fixed preset switch-on period and the variable switch-off period. Especially for motors having bell-shaped armatures, the on-off control mentioned leads to mechanical vibrations in the range of several kHz, thus in the range of greatest hearing sensitivity.
In order to control the speed of rotation of separately excited direct current motors, PID-controllers may also be used in combination with a pulse width generator. In this case, the direct current motor is cyclically controlled by means of a pulse width modulated signal, the induction voltage (counter-EMF) of the motor being determined in the current-free condition of the motor and the pulse width generator then being controlled by means of the PID-controller in accordance with the deviation of the actual value from the set value for the speed of rotation of the motor, in order to generate the pulse width modulated signal. The disadvantage in the case of this method of control is to be seen in particular in that the parameters required for the PID-controller are to be determined only with difficulty. Especially in the slow speed range of the model vehicles, it has proven to be very difficult to optimize these parameters in such a manner that control instabilities are reliably avoided over as wide a control range as possible.
It is an object of the present invention to provide a method of the generic kind for control of the speed of rotation of a separately excited direct current motor for model vehicles which results in only a low level of noise output for the direct current motor and enables stable control over a wide range of speeds of rotation.
SUMMARY OF THE INVENTION
This object is met according to the invention in the case of a method of the kind mentioned at the beginning by a pulse width modulated signal being provided, the pulse width of which is dependent on the average torque loading of the motor, and by the pulse width modulated signal being combined with the pulse sequence by an AND-operation.
The method according to the invention combines the advantages of an on-off controller with those of pulse width modulation, the noise output associated with the on-off controller being however significantly reduced and it being possible to control the speed of rotation in a stable manner over a wide range. Noise output is diminished by the pulse sequence of the on-off controller being combined with a pulse width modulated signal by means of an AND-element, so that the resulting control signal for a switch element by which the supply voltage is provided to the motor, may have a frequency outside the range of human hearing. The stability of the control is increased by the pulse width of the pulse width modulated signal being dependent on the average torque loading of the motor, while a quick reaction to load fluctuations on the motor is assured by the pulse sequence of the on-off controller.
In an especially preferred embodiment of the method, the pulse width corresponding to the average torque loading of the motor is assured by an average value of the pulse sequence being established and a pulse width generator being controlled by means of this average value in order to generate the pulse width modulated signal. The average value of the pulse sequence provided by the on-off controller represents a measure of the average torque load on the motor. For fixed presetting of the switch-on period for the pulse sequence, the average value is greater according as the switch-off period is shorter, that is the greater the set value deviates from the actual value of the speed of rotation of the motor.
In order to guarantee an especially low noise output, it is advantageous for an operating frequency greater than about 17 kHz to be used for the pulse width modulated signal, in particular an operating frequency of approximately 20 kHz. Preferably, the operating frequency is accordingly above the range of human hearing, so that mechanical vibrations of the direct current motor which occur cannot be heard by the user.
It is also an object of the invention, in order to carry out the method mentioned above, to provide a control unit of the kind mentioned at the beginning, which results in a low level of noise output from the direct current motor and enables a wide and stable control range.
This object is met according to the invention in the case of a control unit of the generic kind by the control unit having a pulse width generator which provides a pulse width modulated signal having a pulse width corresponding to an average torque loading of the motor, and by the control unit including an AND-element for combination of the pulse sequence with the pulse width modulated signal.
As already explained, the use of an on-off controller in combination with a pul
Gebr. Maerklin & Cie. GmbH
Lipsitz Barry R.
Martin Edgardo San
Nappi Robert E.
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