Electricity: motive power systems – Positional servo systems – 'reset' systems
Reexamination Certificate
2003-03-10
2004-11-02
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Positional servo systems
'reset' systems
C318S599000, C318S621000, C318S632000
Reexamination Certificate
active
06812668
ABSTRACT:
The present application is based on Japanese Patent Application Nos. 2002-083102 and 2002-190106 respectively filed on Mar. 25, 2002 and Jun. 28, 2002, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to an apparatus, a method and a program for controlling an electric motor by feedback control using a state estimator or an observer and an apparatus and a method for controlling an operating speed of an electric motor by feedback control to drive a movable object such that a moving speed of the movable object coincides with a target speed value.
2. Discussion of Related Art
There is known an apparatus arranged to control an electric motor by feedback control using a state estimator.
FIG. 21
illustrates an example of a feedback control system using a state estimator. This feedback control system includes a state estimator
0
which estimates a state quantity x representative of an internal state of a movable object A, on the basis of a control input u that is a value of a control signal to be applied to an electric motor M, and a control output y representative of an actual operating state of the movable object A as driven by the electric motor M. The control input u to be applied to the electric motor M is generated on the basis of a product of the estimated state quantity x and a gain g, and a product of the gain g and an integrated error (r−y) between a target value r of a control quantity of the electric motor M and the control output y. According to this feedback control, the operation of the electric motor M is controlled such that the control output y eventually coincides with the target value r.
The operating state of the movable object A is usually detected on an output of an encoder, which is arranged to generate encoder signals as the rotor of the electric motor M is rotated. A count of the encoder signals is used as the control output y of the movable object A. When the control input u applied to the electric motor M is a positive value, the angular velocity of the motor M in its forward or normal operating direction is increased according to an absolute value of the control value u. When the control input u is a negative value, on the other hand, the angular velocity of the motor M in its reverse direction is increased, that is, the angular velocity of the motor M in its forward operating direction is reduced, according to the absolute value of the control input u.
However, the motor control apparatus arranged as described above suffers from a risk of temporary operation of the electric motor M (or the movable object) in the direction opposite to the direction in which the motor M is always operated to operate the movable object in the predetermined direction.
Where the electric motor is turned off immediately after the last encoder signal is generated by the encoder provided to detect the operating state of the movable object, there is a comparatively long time interval between the moment at which the motor is turned on again and the moment at which the next encoder signal is to be generated (at which the first encoder signal is to be generated after the motor is turned on again). Where the motor is turned off immediately before the next encoder signal is to be generated by the encoder, there is a comparatively short time interval between the moment at which the motor is turned on again and the moment at which the next encoder signal is to be generated. Thus, the time interval between the moment when the motor is turned on again and the moment at which the next encoder signal is to be generated varies depending upon the moment at which the motor is turned off at the end of the last operation.
Where there is a comparatively long time interval between the moment at which the motor is turned on again and the moment at which the next or first encoder signal is to be generated, only the state quantity x estimated by the state estimator increases during this comparatively long time interval, so that the control signal input to further increase the angular velocity of the motor is applied to the motor. As a result, the count of the encoder signals and the control output y accordingly increase, so that the count of the encoder signals eventually exceeds a value corresponding to the state quantity x as estimated by the state estimator. Consequently, the control signal input to reduce the angular velocity of the motor is applied to the motor. In a transient period immediately after the moment of starting of the motor, the angular velocity of the motor is not so high. In this transient period, therefore, a relatively large amount of reduction of the angular velocity of the motor as represented by the control signal input may cause a risk that the motor is not merely stopped with its operating velocity being zeroed, but the motor is operated in the opposite direction.
Where there is a comparatively short time interval between the moment at which the motor is turned on again and the moment at which the next or first encoder signal is to be generated, the count of the encoder signals and the control output y increase during this comparatively short time interval before the state quantity x estimated by the state estimator increases, so that the control signal input to reduce the angular velocity of the motor is applied to the motor. As in the case where there is a comparatively long time interval between the next or first encoder signal is to be generated after the motor is turned on again, a relatively large amount of reduction of the angular velocity of the motor as represented by the control signal input may cause a risk that the motor is not merely stopped, but the motor is operated in the opposite direction.
After the electric motor is thus operated in the opposite direction, the state quantity x estimated by the state estimator becomes larger than a value corresponding to the count of the encoder (the control output y), so that control signal input to increase the angular velocity of the motor is applied to the motor, whereby the operation of the motor in the opposite direction is terminated in a short time. However, the temporary operation of the motor in the direction opposite to the direction of the normal operation of the motor results in a temporary operation of the movable object in the opposite direction, leading to a considerable amount of vibration of the motor and the movable object.
Where the movable object is a paper feeding mechanism arranged to feed a paper in a printer, the temporary operation of the motor in the opposite direction causes the paper to be fed in the reverse direction during the operation of the paper feeding mechanism to feed the paper in the predetermined forward direction, thus giving rise to a risk of deterioration of accuracy of positioning of the paper.
In a serial printer (e.g., an ink-jet printer) wherein a printing head performs a printing operation on a sheet of paper while the printing head is moved relative to the sheet of paper, a carriage carrying the printing head is moved by a carriage drive motor. To assure high accuracy of positioning of images printed on the sheet of paper, the moving speed of the carriage is required to be controlled with high accuracy, within a predetermined printing area of the sheet of paper. To this end, the moving speed of the carriage is detected by a suitable detector such as an encoder, and an electric current to be applied to the carriage drive motor (CR motor) is controlled according to a suitable control algorithm such as a PID control algorithm such that the detected moving speed of the carriage coincides with a predetermined target speed value, so that a torque generated by the CR motor to drive the carriage is controlled.
In the PID control, control quantities in the form of a proportional control quantity, an integral control quantity and a differential control quantity are calculated on the basis of the detected moving speed of the carriage or a speed error between the detected mov
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Ro Bentsu
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