Electricity: motive power systems – Switched reluctance motor commutation control
Reexamination Certificate
2001-07-03
2003-09-23
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Switched reluctance motor commutation control
C318S132000
Reexamination Certificate
active
06624602
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor driving apparatus adapted to switch an exciting phase according to the position of a rotor to carry out commutation control thereby to perform rotational drive as in a brushless DC motor or a step motor or the like, and more specifically, it relates to a motor driving apparatus adapted to control the commutation of a motor by making use of a position detector for detecting the position of an object driven by the motor.
DESCRIPTION OF THE RELATED ART
As an art for detecting the rotational position of a motor employing a permanent magnet for a rotor as in a brushless DC motor or a step motor or the like, there has conventionally been one that utilizes a counter-electromotive voltage generated in an open phase (unenergized phase) of a stator winding. More specifically, a counter-electromotive voltage obtained from an exciting coil is detected, and the zero-cross point at which the detected counter-electromotive voltage crosses a neutral point voltage is determined so as to detect the position of the rotor. The commutation control in this case is implemented by performing a commutation operation at a point where the phase has been shifted by, for example, 30 degrees from the foregoing zero-cross point.
Therefore, when the motor is at rest, no counter-electromotive voltage can be obtained from the exciting coil, and no sensorless drive can be performed. Hence, to start the motor at rest to rotationally drive it, so-called forced commutation is carried out to forcibly drive the rotor thereby to obtain a counter-electromotive voltage of a predetermined value or more from the exciting coil before proceeding to the sensorless drive.
In contrast to such sensorless control of a motor, there has also been known a method or the like wherein a motor is provided with a Hall element to thereby detect the position of a rotor to drive the motor on the basis thereof.
SUMMARY OF THE INVENTION
However, when conducting the sensorless control based on counter-electromotive voltage, the control cannot be conducted at low speed as described above, making it unsuited for carrying out drive control that involves repetitious stops and starts. According to the method whereby the control is conducted using a Hall element or the like, the control can be conducted even at low speed; however, the variations in the magnetic pole dividing width of the magnetic pole of a rotor, the variations in the position where the Hall element is installed, etc. directly affect control accuracy in the form of commutation timing errors. Hence, in an operation in a speed range wherein counter-electromotive voltages can be detected, the sensorless control based on counter-electromotive voltages is currently stable since it does not involve the errors mentioned above. There has been a demand for a driving method that allows control to be carried out even at low speed and also permits control of a motor with higher accuracy to be achieved.
Accordingly, the present invention has been made with attention focused on the above-mentioned conventional unsolved problems, and it is an object of the present invention to provide a motor driving apparatus capable of reliably carrying out control even at low speed and of controlling the drive of a motor with higher accuracy.
To attain the above object, a motor driving apparatus of the present invention is characterized by the provision of a position detector that outputs a pulse signal as an object driven by a motor travels, and commutation controlling means for controlling the commutation of the motor on the basis of the pulse signal from the position detector.
A pulse signal is output from a position detector or the like provided on an object to be driven by the motor as the object to be driven travels, and the commutation of the motor is controlled on the basis of the pulse signal. More specifically, the object to be driven is driven by the motor, so that the travel of the object to be driven is proportional to the rotational amount of the motor, and the rotational state of the motor can be detected from the traveling state of the object to be driven, thus enabling the detection of the position of the rotor. Hence, by controlling the commutation of the motor on the basis of a detection signal from the position detector, a commutation timing can be precisely detected even if the motor is in a low speed zone.
A motor driving apparatus can also be characterized by the provision of a position detector that outputs a pulse signal as an object driven by a motor travels, and is able to output at least one or more pulses per commutation section of the motor, counting means for adding or subtracting pulses from the position detector according to a rotational direction of the motor, taking a state wherein a rotor of the motor is in an initial position as a reference, commutation pattern storing means for storing a commutation pattern that specifies a commutation timing set on the basis of the number of pulses per commutation section of the motor, and commutation controlling means for performing the commutation of the motor if a count value of the counting means coincides with a commutation pattern stored by the commutation pattern storing means.
When the motor runs, thereby causing an object to be driven to travel, for example, a pulse of a pulse signal from a position detector provided on the object to be driven is counted according to the rotational direction of the motor, and the commutation of the motor is performed when a count value, which uses a reference when the rotor of the motor is at a position based on a commutation timing, coincides with a commutation pattern stored by the commutation pattern storing means. The commutation pattern is set on the basis of the number of pulse signals received per commutation section that has been detected in advance; therefore, commutation will be performed at an exact commutation timing by carrying out commutation at a point where the count value agrees with the commutation pattern.
The motor driving apparatus can further be characterized in that the commutation pattern is constructed by a string of commutation timing values set on the basis of a string of numeric values created by adding the number of section pulses, which is the number of pulses per commutation section, until a sum of the number of section pulses becomes an integral value, rounding off all digits to the right of a decimal point of the sum of the number of section pulses in each adding cycle so as to obtain an integral value, and arranging the integral values in an ascending order, and the commutation controlling means repeatedly switches the commutation timing values in the order in which the commutation timing values are arranged in the commutation pattern, and performs commutation each time the commutation timing value coincides with the count value.
The commutation pattern is constructed by a string of numeric values based on the number of additions performed until the sum of the number of section pulses, which indicates the number of pulses per commutation section, reaches an integral value when the numbers of section pulses are added in sequence. Since the number of section pulses is the number of pulse signal per commutation section, commutation may be performed each time the count value coincides with the number of section pulses. If, however, the number of section pulses is not an integral value, then the commutation timing based on the number of section pulses will be deviated from an actual commutation timing based on a count value.
If an integral value is obtained when the number of section pulses is added several times, then the commutation timing determined on the basis of the number of section pulses agrees with a true commutation timing based on the position of a rotor at the point when the integral value is reached; therefore, no difference in the commutation timing will result at that point. Hence, the number of times of additions performed until an integral value is reached when the numbers of
Ikegami Akihiko
Miyazaki Shinichi
Dang Khanh
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
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