1. An electric motor system comprising:
a brushless direct-current motor having an output shaft for transmitting torque,
the motor rotating at a given rotational speed in a steady operational state thereof, and stopping rotation while being energized in a temporary, hold state thereof;
a driver circuit connected to the motor to supply power to the motor according to a control signal input thereto;
a position sensor adjacent to the motor to measure an angular, rotational position of the motor shaft; and
a control circuit connected between the position sensor and the driver circuit to control operation of the motor, the control circuit including:
a position sensor terminal connected to the position sensor to receive a feedback signal indicating the measured rotational position of the motor shaft;
a reference terminal connected to a reference signal source to receive a reference signal indicating a targeted rotational position of the motor shaft;
a differential calculator connected to the position sensor terminal and the reference terminal to generate an error signal representing a difference between the measured and targeted rotational positions of the motor shaft based on the feedback signal and the reference signal;
a controller connected to the differential calculator to generate the control signal based on the error signal through a combination of control actions, including at least a proportional action and an integral action employing a proportional gain and an integral gain, respectively; and
a gain adjuster connected to the controller to adjust the gain of each control action to a first value where the motor is in the steady operational state thereof, and to a second value different from the first value where the motor is in the hold state thereof.
2. The system according to claim 1, wherein the gain adjuster changes the gain from the first value to the second value where a predetermined time limit has elapsed since entry of the motor into the hold state thereof.
3. The system according to claim 1, wherein the gain adjuster changes the gain from the first value to the second value where the difference between the measured and targeted rotational positions of the motor shaft falls below a first threshold since entry of the motor into the hold state thereof.
4. The system according to claim 1, wherein the gain adjuster changes the gain from the first value to the second value where a predetermined time limit has elapsed since entry of the motor into the hold state thereof, and the difference between the measured and targeted rotational positions of the motor shaft falls below a first threshold since entry of the motor into the hold state thereof.
5. The system according to claim 1, wherein the gain adjuster changes the gain of each control action from the second value to the first value where the motor enters a ramp-up state thereof in which the rotational speed of the motor increases from zero to a given rotational speed.
6. The system according to claim 5, wherein the gain adjuster detects entry of the motor into the ramp-up state thereof based on the error signal indicating that the difference between the measured and targeted rotational positions of the motor shaft exceeds a second threshold.
7. The system according to claim 5, wherein the gain adjuster detects entry of the motor into the ramp-up state thereof based on an output signal from the driver circuit indicative of an operational state of the motor.
8. The system according to claim 5, further comprising a correction circuit connected between the gain adjuster and the driver circuit to correct the control signal for the difference between the measured and targeted rotational positions of the motor shaft upon entry of the motor into the ramp-up state thereof.
9. The system according to claim 1, wherein the second value of the gain of each control action is lower than the first value, so that the combination of control actions employing the second values does not cause a movement of the motor in the hold state thereof.
10. The system according to claim 1, wherein the controller comprises a P-PI controller, with the combination of control actions further including an additional proportional action in addition to the proportional action and the integral action.
11. The system according to claim 1, wherein the controller comprises a PID controller, with the combination of control actions further including a derivative action employing a derivative gain in addition to the proportional action and the integral action.
12. The system according to claim 11, wherein a ratio of the second value with respect to the first value is \xbd for the proportional gain, \xbc for the integral gain, and \xbd for the derivative gain, respectively.
13. An image forming apparatus incorporating the system according to claim 1, wherein the motor drives a roller selected from the group consisting of a feed roller, a registration roller, a transfer roller, an output roller, a belt supporting roller, and combinations thereof.
14. An image forming apparatus incorporating the system according to claim 1, the apparatus comprising:
a photoconductor device defining a photoconductive surface for forming a toner image thereon;
an exposure device with a light source directed to the photoconductor to irradiate the photoconductive surface with light to form an electrostatic latent image thereon; and
a development device adjacent to the photoconductor to render the electrostatic latent image into a visible, toner image,
wherein the motor drives a rotary member included in at least one of the photoconductor device, the exposure device, and the development device.
15. A method for controlling operation of a brushless direct-current motor having an output shaft for transmitting torque, the motor rotating at a given rotational speed in a steady operational state thereof, and stopping rotation while being energized in a hold state thereof,
the method comprising:
acquiring a measured rotational position of the motor shaft;
acquiring a targeted rotational position of the motor shaft;
calculating a difference between the measured and targeted rotational positions of the motor shaft;
generating a control signal based on the calculated difference through a combination of control actions, including at least a proportional action and an integral action employing a proportional gain and an integral gain, respectively;
supplying power to the motor according to the control signal; and
adjusting the gain of each control action to a first value where the motor is in the steady operational state thereof, and to a second value different from the first value where the motor is in the hold state thereof.
16. A circuit for controlling operation of a brushless direct-current motor having an output shaft for transmitting torque, the motor rotating at a given rotational speed in a steady operational state thereof, and stopping rotation while being energized in a hold state thereof,
the circuit comprising:
means for supplying power to the motor according to a control signal;
means for acquiring a measured rotational position of the motor shaft;
means for acquiring a targeted rotational position of the motor shaft;
means for calculating a difference between the measured and targeted rotational positions of the motor shaft;
a PID controller to generate the control signal based on the calculated difference through a combination of control actions, including at least a proportional action and an integral action employing a proportional gain and an integral gain, respectively; and
a gain adjuster connected to the controller to adjust the gain of each control action to a first value where the motor is in the steady operational state thereof, and to a second value different from the first value where the motor is in the hold state thereof.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A position estimation apparatus for a mobile object, said position estimation apparatus comprising:
a position prediction unit configured to drive a position prediction filter to carry out a filtering process on a sensor value generated by an odometry sensor mounted on said mobile object as a sensor value for the present frame and a result of estimating the position of said mobile object for a previous frame in order to produce a position prediction as a prediction of said position of said mobile object for the present frame;
an environment observation unit configured to measure the environment of said mobile object by making use of an environment observation sensor other than said odometry sensor used by said position prediction unit and observing positions of feature points in said environment by keeping track of said feature points from frame to frame;
a prediction-error check unit configured to produce a result of determination as to whether a position prediction produced by said position prediction unit as a prediction of the position of said mobile object is correct or incorrect on the basis of a result generated by said environment observation unit as a result of an operation to keep track of said feature points in said environment;
a position prediction correction unit configured to correct a position prediction produced by said position prediction unit as a prediction of the position of said mobile object if said prediction-error check unit produces a determination result indicating that said position prediction is incorrect; and
a positionposture updating unit configured to update the position andor posture of said mobile object if said prediction-error check unit produces a determination result indicating that a position prediction produced by said position prediction unit as a prediction of the position of said mobile object is correct.
2. The position estimation apparatus according to claim 1 wherein said environment observation unit finds a search range by making use of a position andor a posture, which are predicted by said position prediction unit, and keeps track of said feature points.
3. The posit on estimation apparatus according to claim 2 wherein said environment observation unit:
estimates positions of said feature points from positions known in advance as positions of said feature points in a three-dimensional space and from data estimated by a Kalman filter as the positional data of said mobile object;
deforms a template seen from the position of said mobile object as a template of the vicinity of each of said feature points in accordance with affinity constraints from luminance image data in the vicinity of each of said feature points and from posture data of a luminance image in said vicinity of each of said feature points; and
keeps track of said feature points by adoption of a template matching technique on the basis of said search range and said templates.
4. The position estimation apparatus according to claim 1 wherein said prediction-error check unit:
counts the number of feature points each successfully passing an operation carried out by said environment observation unit to keep track of said feature points and the number of feature points failing in the same operation; and
produces a determination result indicating that a position prediction produced by said position prediction unit as a prediction of the position of said mobile object is correct if said operation to keep track of feature points has been carried out by said environment observation unit at a success rate higher than a certain probability; or otherwise,
produces a determination result indicating that said position prediction produced by said position prediction unit as a prediction of the position of said mobile object is incorrect.
5. The position estimation apparatus according to claim 1 wherein said positionposture updating unit makes said position prediction unit use an estimation result of a position, which has been updated by said positionposture updating unit as the position of said mobile object, in an operation to produce a position prediction for the next frame as an estimation result of the position of said mobile object for the previous frame.
6. The position estimation apparatus according to claim 2 wherein said position prediction correction unit changes an existence probability distribution model showing a distribution of probabilities of existence of said mobile object in order to increase the value of the standard deviation of said existence probability distribution model and hence increase the width of said search range used by said environment observation unit if said prediction-error check unit produces a determination result indicating that a position prediction produced by said position prediction unit as a prediction of the position of said mobile object is incorrect.
7. A position estimation method for a mobile object, said position estimation method comprising the steps of:
driving a position prediction filter to carry out a filtering process on a sensor value generated by an odometry sensor mounted on said mobile object as a sensor value for the present frame and a result of estimating the position of said mobile object for a previous frame in order to produce a position prediction as a prediction of the position of said mobile object for the present frame;
measuring the environment of said mobile object by making use of an environment observation sensor other than said odometry sensor used in said position prediction process and observing positions of feature points in said environment by keeping track of said feature points from frame to frame;
producing a result of determination as to whether a position prediction produced in said position prediction process as a prediction of the position of said mobile object is correct or incorrect on the basis of a result generated in said environment observation process as a result of an operation to keep track of said feature points in said environment;
correcting a position prediction produced in said position prediction process as a prediction of the position of said mobile object if said prediction-error check process produces a determination result indicating that said position prediction is incorrect; and
updating the position andor posture of said mobile object if said prediction-error check process produces a determination result indicating that a position prediction produced in said position prediction process as a prediction of the position of said mobile object is correct.
8. A recording medium configured to record a position estimation program to be executed by a position estimation apparatus configured to predict the position of a mobile object wherein said position estimation program comprises:
a position prediction process of driving a position prediction filter to carry cut a filtering process on a sensor value generated by an odometry sensor mounted on said mobile object as a sensor value for the present frame and a result of estimating the position of said mobile object for a previous frame in order to produce a position prediction as a prediction of the position of said mobile object for the present frame;
an environment observation process of measuring the environment of said mobile object by making use of an environment observation sensor other than said odometry sensor used in said position prediction process and observing positions of feature points in said environment by keeping track of said feature points from frame to frame;
a prediction-error check process of producing a result of determination as to whether a position prediction produced in said position prediction process as a prediction of the position of said mobile object is correct or incorrect on the basis of a result generated in said environment observation process as a result of an operation to keep track of said feature points in said environment;
a position prediction correction process of correcting a position prediction produced in said position prediction process as a prediction of the position of said mobile object if said prediction-error check process produces a determination result indicating that said position prediction is incorrect; and
a positionposture updating process of updating the position andor posture of said mobile object if said prediction-error check process produces a determination result indicating that a position prediction produced in said position prediction process as a prediction of the position of said mobile object is correct.