Stepping motor control unit and method, printer employing the same, and information recording medium

• US 6,259,225 B1
• Filed: 08/05/1999
• Issued: 07/10/2001
• Est. Priority Date: 12/10/1997
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Matsumoto, Yoshiharu
• Primary Examiner(s): Masih, Karen
• Application Number:
  US09/367,066
• Time in Patent Office: 705 Days
• Field of Search: 318/696, 318/685, 318/138, 318/254, 318/439, 310/216
• US Class Current: 318/696
• CPC Class Codes: B41J 11/42 Controlling printing material conveyance for accurate alignment of the printing material with the printhead; Print registering
• CPC Class Codes: H02P 8/14 Arrangements for controlling speed or speed and torque H02P8/12, H02P8/22 take precedence

Abstract

A stepping motor control unit is capable of driving a stepping motor fast through feedback control. Slits bored in a disk fixed to a rotor of a stepping motor are located at positions that precede magnetically stable positions of the rotor in a direction of rotation of the rotor. Light passing through the slits is detected by an optical sensor, and a signal t is output thereby. The signal t is delayed by a predetermined time according to the rotating speed of the rotor and then transmitted to a control unit. The control unit receives a position detection signal earlier according to the rotating speed of the rotor. Therefore, the wait time required for switching phases can be shortened. Moreover, when the signal t is generated twice or more during a signal t detection time during which a signal t indicating a certain phase is detected, the second and subsequent signals t are ignored. Thus, incorrect detection can be avoided.

Claims

1. A stepping motor control unit, comprising:

(a) an electromagnet having a plurality of excitable phases;

(b) a rotor assembly having a plurality of slits formed therein, and a plurality of stable positions, each of which corresponds to a respective one of the plurality of phases of the electromagnet;

(c) a sensing element that detects the position of the rotor assembly, wherein the plurality of slits are positioned on the rotor assembly such that at least one edge of a given slit is offset by a predetermined angle relative to the sensing element when the rotor assembly is in a corresponding stable position, and wherein the sensing element detects the position of the rotor assembly as it rotates between a first stable position and a second stable position at the predetermined angle before the rotor assembly reaches the second stable position relative to the direction of rotation and outputs a detection signal; and

(d) a control circuit that selectively controls the excitation of each of the plurality of phases of the electromagnet in response to the detection signal and a corresponding one of a plurality of predetermined step times based on the rotational speed of the rotor assembly, wherein the control circuit excites the phase of the electromagnet corresponding to a third stable position of the rotor assembly at a predetermined time after receiving the detection signal.

2. A stepping motor control unit according to claim 1, further comprising:

(e) a delay circuit that delays the detection signal output by the sensing element by a predetermined delay time based on the rotating speed of the rotor assembly and then outputs the detection signal to the control circuit.

3. A stepping motor control unit according to claim 1, wherein the predetermined angle is an electrical angle within a range of 15°

to 35°

.

4. A stepping motor control unit according to claim 1, wherein the rotor assembly includes a rotor and a disk fixed to the rotor, wherein the plurality of slits are formed in the fixed disk, and wherein the sensing element comprises an optical sensor that detects light as it selectively passes through each of the plurality of slits and outputs the detection signal based on the detection result.

5. A stepping motor control unit according to claim 1, further comprising a filter, wherein, if a plurality of detection signal pulses are detected by the control circuit during a detection signal detection time, the filter inhibits all but the first pulse detected during the detection signal detection time.

6. A stepping motor control unit according to claim 5, further comprising a recording medium that records the plurality of predetermined step times, a plurality of delay times, and a plurality of detection times, each associated with a corresponding one of the plurality of predetermined step times, wherein the control unit controls the excitation of each of the plurality of phases of the electromagnet in response to the detection signal and the plurality of delay, step and detection times recorded in the recording medium.

7. A stepping motor control unit according to claim 5, wherein each of the plurality of detection times shortens as a rotating speed of the rotor assembly increases proportionally to the step times.

8. A print head moving unit for a printer using a stepping motor control unit set forth in claim 1 to supply power by which a print head of a printer is moved.

9. A paper feeding unit for a printer using a stepping motor control unit set forth in claim 1 to supply power by which a paper feeding mechanism of a printer is driven.

10. A printer having a stepping motor control unit set forth in claim 1.

11. A stepping motor control unit according to claim 1, wherein the at least one edge of the given slit is aligned with the sensing element before the rotor assembly reaches the corresponding stable position.

12. A stepping motor control unit according to claim 1, wherein each slit has first and second radially extending edges, the first radially extending edge of the given slit being offset in a first direction by the predetermined angle relative to the sensing element when the rotor assembly is in the corresponding stable position and the second radially extending edge of the given slit being offset in a second direction opposite the first direction by the predetermined angle relative to the sensing element when the rotor assembly is in the corresponding stable position.

13. A stepping motor control method employing an electromagnet having a plurality of excitable phases, a rotor assembly having a plurality of slits formed therein, and a plurality of stable positions, each of which corresponds to a respective one of the plurality of phases of the electromagnet, and a sensing element that detects the position of the rotor assembly, wherein the plurality of slits are positioned on the rotor assembly such that at least one edge of a given slit is offset by a predetermined angle relative to the sensing element when the rotor assembly is in a corresponding stable position, said method comprising the steps of:

(a) detecting the position of the rotor assembly at the predetermined angle before the rotor assembly reaches each stable position relative to the direction of rotation and outputting a detection signal; and

(b) selectively controlling the excitation of each of the plurality of phases of the electromagnet in response to the detection signal and a corresponding one of a plurality of predetermined step times based on the rotational speed of the rotor assembly.

14. A stepping motor control method according to claim 13, wherein the detecting step (a) comprises:

(a)(1) detecting the rotor assembly as it rotates between a first stable position and a second stable position at the predetermined angle before reaching the second stable position; and

wherein the controlling step (b) comprises;

(b)(1) exciting the phase of the electromagnet corresponding to a third stable position of the rotor assembly at a predetermined time after the control circuit receives the detection signal.

15. A stepping motor control method according to claim 13, further comprising the step of:

(c) delaying the detection signal output in the detecting step (a) by a predetermined delay time based on the rotating speed of the rotor assembly and then outputting the detection signal to the control circuit.

16. A stepping motor control method according to claim 13, wherein the detecting step (a) comprises:

(a)(1) filtering all but a first pulse detected during the detection signal detection time if a plurality of detection signal pulses are detected during a detection signal detection time.

17. An information recording medium embodying a program of instructions for controlling a stepping motor that has an electromagnet having a plurality of excitable phases, a rotor assembly having a plurality of slits formed therein, and a plurality of stable positions, each of which corresponds to a respective one of the plurality of phases of the electromagnet, and a sensing element that detects the position of the rotor assembly, wherein the plurality of slits are positioned on the rotor assembly such that at least one edge of a given slit is offset by a predetermined angle relative to the sensing element when the rotor assembly is in a corresponding stable position, the program of instructions comprising:

(a) instructions on the medium for detecting the position of the rotor assembly at the predetermined angle before the rotor assembly reaches each stable position relative to the direction of rotation and outputting a detection signal; and

(b) instructions on the medium for selectively controlling the excitation of each of the plurality of phases of the electromagnet in response to the detection signal and a corresponding one of a plurality of predetermined step times based on the rotational speed of the rotor assembly.

18. An information recording medium according to claim 17, wherein the detecting instructions (a) comprises:

(a)(1) instructions on the medium for detecting the rotor assembly as it rotates between a first stable position and a second stable position at the predetermined angle before reaching the second stable position; and

wherein the controlling instructions (b) comprises;

(b)(1) instructions on the medium for exciting the phase of the electromagnet corresponding to a third stable position of the rotor assembly at a predetermined time after the control circuit receives the detection signal.

19. An information recording medium according to claim 17, further comprising:

(c) instructions on the medium for delaying the outputted detection signal by a predetermined delay time based on the rotating speed of the rotor assembly and then outputting the detection signal to the control circuit.

20. An information recording medium according to claim 17, wherein the detecting instructions (a) comprises:

(a)(1) instructions on the medium for filtering all but a first pulse detected during the detection signal detection time if a plurality of detection signal pulses are detected during a detection signal detection time.