Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-12-17
2004-10-19
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000, C347S014000
Reexamination Certificate
active
06805426
ABSTRACT:
The present application is based on Japanese Patent Application No. 2001-387759 filed Dec. 20, 2001, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for controlling an operating speed of a motor provided to move an object body, such that a moving speed of the object body coincides with a predetermined target value.
2. Discussion of Related Art
In a conventional printer (e.g., an ink-jet printer) of a type wherein a printing head performs a printing operation on a sheet of paper during a movement of the printing head, an electric motor (hereinafter referred as “CR motor”) is used to drive a carriage which carries the printing head. To assure printing actions exactly as predetermined printing positions, a moving speed of the carriage is required to be held constant within a predetermined range or distance of printing. To this end, the moving speed of the carriage is detected by using an encoder, and an electric current to be applied to the CR motor is controlled according to a suitable control algorithm such as a PID algorithm, such that the detected moving speed coincides with a predetermined target value, so that a torque generated by the motor, namely, a drive force required to move the carriage is controlled.
Generally, a direct current (DC) motor is used as the CR motor. It is known that the DC motor has a variation in torque, or so-called “cogging” of torque, which takes place due to a variation in a magnetic attracting force produced between a stator and a rotor of the motor.
This cogging of torque disturbs a predetermined linear relationship between the drive current and the torque of the CR motor. Accordingly, a PID or other closed-loop control of the drive current of the CR motor having the cogging torque has a risk that the torque variation (speed variation) at the cogging frequency is undesirably amplified, resulting in considerable deterioration in the stability of the operating speed of the CR motor.
Described in detail, even when the drive current is adequately controlled so as to control the motor speed to the target value, the detected moving speed of the carriage has an error with respect to the target value at angular positions of the motor at which the torque cogging takes place. Since the drive current is conventionally controlled so as to eliminate this error, the operating speed of the motor cannot be controlled with a high degree of stability.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to control an electric motor provided to move an object body, such that the operating speed of the motor is controlled with high stability, to permit a printing operation with high image resolution, for example. This object may be achieved according to any one of the following modes of the present invention in the form of a motor control method or a motor control apparatus, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, for easier understanding of technical features disclosed in the present application and possible combinations of those features. However, it is to be understood that the invention is not limited to those technical features or combinations thereof, and that any one of a plurality of technical features described below with respect to any one mode of the invention may be a subject matter of the present invention, without the other technical feature or features being combined with that one technical feature.
(1) A method of controlling an operating speed of a motor provided to move an object body such that a moving speed of the object body coincides with a predetermined target value, comprising the steps of:
obtaining a speed control error between the target value and a speed value represented by a filtered speed signal obtained by removing a component having a frequency not lower than a predetermined threshold value, from an original speed signal corresponding to the moving speed of the object body; and
controlling the operating speed of the motor according to a control signal generated on the basis of results of a proportional calculating operation and an integral calculating operation of the speed control error, and a result of a differential calculating operation of the original speed signal.
In the motor control method according to the above mode (1) of this invention, the component (hereinafter referred to as “specific-frequency component”) which has a frequency not lower than the predetermined threshold value and which is included in the original speed signal is removed to obtain the filtered speed signal which is used to obtain the speed control error, which is used for the proportional and integral calculating operations. Accordingly, a periodic variation in the moving speed of the object body is not amplified due to the specific-frequency component, by a feedback control of the operating speed of the motor according to the control signal. On the other hand, the differential calculating operation is performed with respect to the original speed signal which includes the specific-frequency component.
Accordingly, the present motor control method not only prevents deterioration of stability of the moving speed of the object body due to the specific-frequency component included in the original speed signal, but also effectively minimizes minute variations in the moving speed of the object body due to the component having a frequency higher than the predetermined threshold value.
(2) A method according to the above mode (1), wherein the predetermined threshold value is not higher than a cogging frequency of the motor.
The predetermined threshold value of the frequency is preferably selected to be equal to or lower than the cogging frequency of the motor, where the motor is a direct-current (DC) motor, a stepping motor or any other motor which inevitably suffers from cogging of its torque.
(3) A method according to the above mode (1) or (2), wherein the object body is a carriage which carries a printing head.
Where the object body is a carriage carrying a printing head, the present motor control method permits a significant improvement in the quality of an image printed by the printing head.
In a printer, vibrations of various elements of the printer as well as the cogging torque of the motor influence the speed signal. In particular, minute variations in the moving speed (i.e., printing positions) of the carriage generated due to a signal component having a high frequency have a considerable adverse influence on the resolution of the printed image. These minute variations can be minimized by the differential calculating operation which is performed with respect to the original speed signal including such a high frequency component.
(4) A method according to any one of the above modes (1)-(3), wherein the control signal is generated by subtracting the result of the differential calculating operation from a sum of the results of the proportional and integral calculating operations.
(5) A method according to any one of the above modes (1)-(4), wherein the operating speed of the motor is controlled according to the control signal until the object body has reached a predetermined deceleration-start position at which deceleration of the object body is initiated.
(6) A method according to any one of the above modes (1)-(4), wherein the operating speed of the motor is controlled according to the control signal while the object body is moved between a predetermined acceleration-end position and a predetermined deceleration-start position at which acceleration and deceleration of the object body are terminated and initiated, respectively.
(7) A method according to any one of the above modes (1)-(6), wherein the predetermined threshold value is changed depending upon the target value of the operating speed of the object body.
(8) A motor control apparatus for controlling an operating speed of a motor provided to move an object body, the motor control app
Akiyama Shigeki
Kokubo Masatoshi
Brother Kogyo Kabushiki Kaisha
Dudding Alfred
Meier Stephen D.
Oliff & Berridg,e PLC
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