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EP-3829052-B1 - MOTOR CONTROL APPARATUS AND IMAGE FORMING APPARATUS WITH LIMITING COIL CURRENT FLOWING THROUGH MOTOR COIL

EP3829052B1EP 3829052 B1EP3829052 B1EP 3829052B1EP-3829052-B1

Inventors

  • ITOH, MASATOSHI

Dates

Publication Date
20260513
Application Date
20201105

Claims (12)

  1. A motor control apparatus comprising: setting means (31) adapted to set a limit value (IL) of coil current flowing through a coil of a motor; current supply means (121) adapted to supply the motor with the coil current in a range not exceeding the limit value set by the setting means; detection means (128) adapted to detect a current value of the coil current; and comparison means (31) adapted to compare an average value (Iave) of the current value detected by the detection means (128) over a predetermined time period with a first temperature rise threshold value (Th), the first temperature rise threshold value (Th) being smaller than the limit value (IL), wherein the setting means (31) is adapted to update the limit value (IL) in a decreasing manner, when the average value (lave) has exceeded the first threshold value, characterized in that , the first temperature rise threshold value (Th) is determined based on the current value of the coil current that turns a coil temperature into a rated temperature, and is in that the current supply means is adapted to supply the motor with the coil current for rotating a rotor of the motor at a predetermined target speed, and an initial value of the limit value set by the setting means is larger than a value of the coil current required to rotate the rotor at the predetermined target speed relative to load variation in a steady load state under normal operation of the motor.
  2. A motor control apparatus comprising: setting means (31) adapted to set a limit value (VL) of rotation speed of a rotor of a motor; determination means (31) adapted to determine a target value of a rotation speed of the rotor based on a target speed initial value (VTD) and the limit value (VL); current supply means (121) adapted to supply a coil of the motor with coil current for rotating the rotor at the target value; and detection means (128) adapted to detect a current value of the coil current; characterized by comparison means (31) adapted to compare an average value (Iave) of the current value detected by the detection means (128) over a predetermined time period with a first temperature rise threshold value (Th), the first temperature rise threshold value (Th) being determined based on the current value of the coil current that turns a coil temperature into a rated temperature, wherein, when the average value (Iave) has exceeded the first temperature rise threshold value (Th), the setting means (31) is adapted to update the limit value (VL) in a decreasing manner, and the determination means (31) is adapted to determine a smaller one of the limit value (VL) and the target speed initial value (VTD) to be the target value.
  3. The motor control apparatus according to claim 2, wherein the target speed initial value is lower than an initial value of the limit value.
  4. The motor control apparatus according to claim 2 or 3, wherein the current supply means is adapted to supply the motor with the coil current in a range not exceeding a predetermined maximum value and the maximum value is larger than a value of the coil current required to rotate the rotor at the target speed initial value relative to load variation in a steady load state under normal operation of the motor.
  5. The motor control apparatus according to any one of claims 1 to 4, wherein, when the average value has exceeded the first temperature rise threshold value, the setting means is adapted to update the limit value in a decreasing manner by a first predetermined value.
  6. The motor control apparatus according to any one of claims 1 to 4, wherein, when the average value has exceeded the first threshold temperature rise value, the setting means is adapted to update the limit value in a decreasing manner by a decrement value obtained based on difference between the average value and the first temperature rise threshold value.
  7. The motor control apparatus according to claim 6, wherein the setting means is adapted to increase the decrement value, as the difference between the average value and the first temperature rise threshold value becomes larger.
  8. The motor control apparatus according to any one of claims 1 to 7, wherein, when the average value is lower than a second temperature rise threshold value, the setting means is adapted to update the limit value in an increasing manner, and the second temperature rise threshold value is lower than the first temperature rise threshold value.
  9. The motor control apparatus according to claim 8, wherein, when the average value is lower than the second temperature rise threshold value, the setting means is adapted to update the limit value in an increasing manner by a second predetermined value.
  10. The motor control apparatus according to claim 8, wherein, when the average value is lower than the second temperature rise threshold value, the setting means is adapted to update the limit value in an increasing manner by an increment value obtained based on difference between the average value and the second temperature rise threshold value.
  11. The motor control apparatus according to claim 10, wherein the setting means is adapted to increase the increment value, as the difference between the average value and the second temperature rise threshold value becomes larger.
  12. An image forming apparatus comprising: image forming means (11, 13, 15, 16, 18, 19, 29, 30) adapted to form an image on a sheet; a motor (101) for rotationally driving a rotating member of the image forming means; and a motor control apparatus according to any one of claims 1 to 11.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a motor control technique. Description of the Related Art A brushless motor is used as the drive source of a rotating member in an image forming apparatus. Japanese Patent Laid-Open No. JP 2001-209276 A discloses a configuration that limits the motor operating current based on a limit value. Along with downsizing of image forming apparatuses in recent years, brushless motors (hereinafter simply referred to as "motors") serving as the drive source of rotating members in such image forming apparatuses are also required to be downsized. Here, an unexpected increase of motor load may result in a rise of coil temperature due to an increase of current flowing through the coil of the motor (hereinafter, coil current). When the coil temperature eventually exceeds the insulation temperature of the coil, there may occur a motor failure. For example, using a motor with a small margin relative to the required output to downsize the motor makes the coil temperature more likely to exceed the insulation temperature of the coil in case of an unexpected increase of motor load, whereby a motor failure may occur more frequently. However, excessively limiting the coil current in order to prevent motor failure may hinder proper handling of load variation under normal operation. Document US 5040630 A discloses a power steering system of a motor drive type wherein a motor current controller regulates the maximum level of motor current in accordance with the mean motor current determined at predetermined intervals of time. Furthermore, document US 2016/072415 A1 discloses a method of monitoring an electric motor serving to drive a pump, wherein within a time interval current values are measured, an average value of the current values measured is determined and said average value is compared to a predetermined reference value. A maximum permissible value for a motor feed current predetermined by the motor control is reduced if the average value of the current values measured is greater than the predetermined reference value. Still further, document US 2015/207438 A1 refers to an inverter apparatus for controlling an AC motor included in an electric compressor. Moreover, according to document JP 3 241784 B2, a basic speed command No is compared with a rotational speed signal to produce a speed error signal which is subjected to an automatic speed regulation APR to produce a current command signal. When a DC input current exceeds an input current limit value, the APR generates a speed correction signal which is subtracted from the basic speed command No thus lowering the number of revolution of the fan motor. SUMMARY OF THE INVENTION The present invention in its first aspect provides a motor control apparatus as specified in claims 1 to 11. The present invention in its second aspect provides an image forming apparatus as specified in claim 12. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a configuration diagram of an image forming apparatus according to one embodiment;FIG 2 is a configuration diagram of a motor control unit according to one embodiment;FIG 3 is a configuration diagram of a motor according to one embodiment;FIG 4A illustrates a relation between the load torque and the coil current;FIG 4B illustrates relations of the load torque with the coil temperature and the switching element temperature, respectively.FIG 5 illustrates a variation of coil current due to the load variation under normal load;FIGS. 6A and 6B are explanatory diagrams of motor control according to one embodiment;FIG 7 is a flowchart of motor control according to one embodiment;FIGS. 8A and 8B are explanatory diagrams of motor control according to one embodiment; andFIG 9 is a flowchart of motor control according to one embodiment. DESCRIPTION OF THE EMBODIMENTS Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. First Embodiment FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus forms a full color image by superimposing toner images including four colors: yellow (Y), magenta (M), cyan (C), and black (K). In FIG. 1, Y, M, C, and K at ends of reference numerals indicate that the colors of the toner images involved in the formation of members indicated by the reference numerals are yellow, magenta, cyan, and black. In the following description, when it is not necessary to distinguish the colors from each other, reference numerals excluding Y, M, C, an