Stepping motor drive control system

Abstract: In a stepping motor drive control mechanism, a step drive command is applied sequentially at irregular intervals to drive a stepping motor. Therein, when the step drive command is applied, the stepping motor is driven by one step angle. According to the response characteristic of the stepping motor, an inhibited period when the reception of the next step drive command is inhibited and a reception period when the reception is enabled are set up. If the next step drive command is applied during the inhibited period, the system waits until the reception period comes. Then, the stepping motor is driven by one step angle.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a stepping motor drive control system suitable for a facsimile system, or more particularly, to a stepping motor drive control system which optimizes precision in rotation of a motor. Related Background Art It is known to use a stepping motor for sheet transportation in a facsimile system. The stepping motor is driven by one step angle upon reception of a step drive command. The motor drive can be controlled so that sheet feed in a facsimile system can be done continuously or intermittently, or stopped temporarily, depending on how the step drive commands are provided. The time elapsed from when a step drive command is provided to the stepping motor of a facsimile system until when the next step drive command is provided is rarely uniform but often variable. With the stepping motor, the intervals between the step drive commands can vary largely. Therefore, the stepping motor has come to be used for a facsimile system. Figure 1 shows a general response characteristic in a case where a stepping motor is driven with a step drive command. A rotor of the stepping motor attains a stable state while subject to decreasing vibrations. The stepping motor shows such a response characteristic. In a stepping motor employed for a prior facsimile system, a minimum response time shown with A in Figure 1 is determined, and the next drive command is applied after time A when the rotor has moved one step angle. Therefore, the aforesaid prior stepping motor for facsimile systems would be effective for continuous drive control with uniform intervals between the step drive commands. However, when the intervals between the step drive commands vary largely, the problems below attributable to the response characteristic of the stepping motor are inevitable. When the intervals between the step drive commands vary largely, a next step drive command may be applied during time B or time C in Figure 1. During times B and C, the angular position of a rotor varies greatly. The directivity of the rotor varies largely, too. For sheet transportation in a facsimile system, the inertial force and backlash of a driving system are added. Comparing between the operation when the next step drive command is applied during time B in Figure 1 and the operation when the next step drive command is applied during time C in Figure 1, the operating states of the stepping motor are completely different. When the next step drive command is applied during time B in Figure 1, the stepping motor is oriented in the rotating direction and, therefore, the operation of the stepping motor is stable. When the next step drive command is applied during time C in Figure 1, the stepping motor is oriented inversely from the rotating direction and, therefore, the operation of the stepping motor is unstable. This causes noise and vibrations in sheet transportation of a facsimile system. The aforesaid problems are negligible for an expensive system equipped with a stepping motor having a sufficient size and a highly precise structure, but very serious for a compact and low-price system. Facsimile systems have remarkably spread into our societies. There is a growing demand for a compact and low-price system with high precision. A stepping motor employed for such a system has been designed to be compact and low-price. Therefore, the aforesaid problems associated with the stepping motor employed for a compact and low-price facsimile system are gaining people's attentions. SUMMARY OF THE INVENTION An object of the present invention is to solve the aforesaid drawbacks. More particularly, this invention attempts to provide a stepping motor drive control system which optimizes precision in rotation of a stepping motor which is driven with a step drive command applied at irregular intervals. In accordance with the invention, this object is achieved by a stepping motor drive control system as specified in claim 1 or claim 6. Anoher object of the invention is to permit high-precision sheet feed control using a compact and low-price stepping motor for sheet transportation in a facsimile system. Other objects will be apparent in conjunction with the embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a response characteristic of a stepping motor related to the present invention when the motor is driven with a step drive command. Figure 2 is a block diagram an electric control circuit for the stepping motor of a facsimile system embodying the invention. Figure 3 is a flowchart of the control circuit shown in Figure 2. Figure 4 shows a response characteristic of a stepping motor of an embodiment different from the one in Figure 1. Figure 5 is a diagram of an electric control circuit for the stepping motor shown in Figure 2 which includes one timer. Figure 6 is a flowchart of the control circuit shown in Figure 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is described below in conjunction with the drawings. In this embodiment, a stepping motor is employed for sheet transportation in a facsimile system. Figure 2 shows an electric control circuit of a stepping motor for a facsimile system. 1 represents a main CPU. 2 is a slave CPU having timers T1 and T2, a controller 2₁, and a current controller 2₂. The timers T1 and T2 in the slave CPU 2 are initialized at the start of a communication. The timer T2 is set to a minimum response time. 3 is a motor driver, and 4, a stepping motor. The stepping motor 4 is driven by one step angle with a step drive command. Depending on the way how the main CPU 1 provides step drive commands, the stepping motor 4 realizes such drive control that sheet feed in the facsimile system will be done continuously or intermittently, or stopped temporarily. In the facsimile system, the main CPU 1 provides the step drive commands for driving the stepping motor 4 at irregular intervals. This is because the time elapsed from when a step drive command is provided until when the next step drive command is provided is rarely uniform but often variable. The intervals between the step drive commands vary greatly. Therefore, the main CPU 1 provides the step drive commands in such a way that the minimum response time is determined as A in Figure 1, and then the next step command is applied in time A when the rotor has moved one step angle. The slave CPU 2 sets the phase excitation timing for the motor driver 3 and controls current when a step drive command is applied by the main CPU 1. With the timers T1 and T2 installed, the slave CPU 2 executes the step drive command or inhibits the execution. These timers monitor if the time elapsed from the previous step drive command is within an inhibited period or a reception period, when the second or subsequent step drive command is sent from the main CPU 1 to the slave CPU 2. The inhibited period when the execution of a step drive command is inhibited and the reception period when the execution is enabled are determined according to the response characteristic of the stepping motor 4 shown in Figure 1. Taking into account the position and directivity of the rotor of the stepping motor 4, a period when the operation of the stepping motor 4 is stabilized is defined as reception period, and a period when the operations are unstable, as inhibited period. A period a when the orientation of the rotor coincides with the rotating direction of the stepping motor but the angular position of the rotor has not attained one step angle is an inhibited period. A period b when the orientation of the rotor coincides with the rotating direction of the stepping motor and the angular position of the rotor has attained to or beyond one step angle is a reception period. A period c when after the rotor oscillates at the period b, the orientation of the rotor does not coincide with the rotating direction of the stepping motor or the angular position of the rotor does not attain one step angle is an inhibited period. A period d when the directivity of the rotor gets very weak and the angular position of the rotor converges at one step angle is a reception period. The operations of the aforesaid configuration are described using the flowchart shown in Figure 3. First of all, assume that the main CPU 1 issues a first step drive command to the slave CPU 2. A facsimile communication starts. With a start signal, timers T1 and T2 are initialized at a step S1. At a step S2, the main CPU 1 applies a step drive command to the slave CPU 2. At a step 3, it is determined if the timer T2 value indicates a reception period. The value of the initialized timer T2 represents a minimum response time. Therefore, control is passed to a step S4. Then, the timer T2 is cleared to zero. At a step S5, a step control operation is started. That is to say, the current controller is actuated to enable the stepping motor 4 to start a one-step angular motion. At a step S6, the timer T1 starts to perform a counting operation. At a step S7, the timer T1 is left intact until a time required for the stepping motor 4 to make a multi-step angular motion according to a step angle mode of the stepping motor 4 has elapsed. At a step S8, the timer T1 is cleared to zeros. At a step S9, the step control operation is stopped. Then, the timer T2 starts to perform the counting operation at a step S10. Next, assume that the main CPU 1 applies the second or subsequent step drive command to the slave CPU 2. In this case, the operating sequence starts at the step S2. At the step S2, the main CPU 1 applies the second or subsequent step drive command to the slave CPU 2. At the step S3, it is determined if the timer T2 value indicates the reception period. If it indicates the reception period, control is passed to the step S4. If the timer T2 value indicates an inhibited period, the system waits until the timer T2 value indicates the reception period. When the reception period comes, control is passed to the step S4. The operations at and after the step S4 are identical to those when the first step drive command is applied to the slave CPU 2. Therefore, the description is omitted. Thus, when the second or subsequent step drive command is given to the slave CPU 2, the timer T2 counts the time passed after the previous step drive command. If the value indicates the reception period, the stepping motor is driven by one step angle. If the value indicates the inhibited period, the system waits until the timer T2 value indicates the reception period. When the reception period comes, the stepping motor is driven by one step angle. In the aforesaid embodiment, the inhibited period when the execution of the step drive command is inhibited and the reception period when the execution is enabled are determined according to the response characteristic of the stepping motor shown in Figure 1. The present invention is not confined to this response characteristic of the stepping motor. The response characteristic of any stepping motor causing diverse oscillations can be used. For instance, the response characteristic of a stepping motor shown in Figure 4 can be used. When determining the inhibited and reception periods, consideration must be taken to the position and directivity of the rotor of the stepping motor. Then, a period when the operation of the stepping motor is stabilized is defined as the reception period. A period when the operation of the stepping motor is unstable is defined as the inhibited period. In Figure 4, a period a₁ is defined as inhibited period, and a period b₁ as reception period. In a period c₁, periods c₁₁ and c₁₃ are inhibited periods, and a period c₁₂ a reception period. A period d is defined as a reception period. These periods are defined based on the same standards as those for Figure 1. If all the the c₁ periods are defined as inhibited periods, the program contained in the slave CPU 2 can be simplified. As a result, the price of the facsimile system can be minimized. Using the aforesaid embodiments, motor drive control for a stepping motor used for sheet transportation in a facsimile system is described. In the facsimile system, the sheet feed speed varies depending on the mode. Therefore, two timers T1 and T2 are needed. For a facsimile system supporting only one mode, only one timer T is installed as shown in Figure 5. The operations of the facsimile system are performed according to the flowchart shown in Figure 6. The operations of the aforesaid configuration are described below using the flowchart shown in Figure 6. First of all, assume that the main CPU 1 applies the first step drive command to the slave CPU 2. A facsimile communication starts. With a start signal, the timer T is initialized at a step S11. At a step S12, the main CPU 1 applies a step drive command to the slave CPU 2. At a step S13, it is determined if the timer T value indicates a reception period. The value of the initiated timer T represents a minimum response time. Therefore, control is passed to a step S14. Then, the timer T is cleared to zero. At a step S15, a step control operation is started. That is to say, a current controller is actuated to enable a stepping motor to start a one-step angular motion. At a step S16, the timer T is started to perform a counting operation. At a step S17, the timer T is left intact until a time required for the stepping motor to make a one-step angular motion has elapsed. At a step S18, the step control operation is stopped. Next, assume that the main CPU 1 issues the second or subsequent step drive command to the slave CPU 2. The operating sequence starts at the step S12. At the step S12, the main CPU 1 applies the second or subsequent step drive command to the slave CPU 2. At the step S13, it is determined if the timer T value indicates the reception period. If the value indicates the reception period, control is passed to the step S14. If the value indicates an inhibited period, the system waits until the timer T value indicates the reception period. When the reception period comes, control is passed to the step S14. The operations at and after the step S14 are identical to those when the first step drive command is applied to the slave CPU 2. Therefore, the description is omitted. Thus, when the second or subsequent step drive command is applied to the slave CPU 2, the timer T counts the time elapsed after the previous step drive command. If the value indicates the reception period, the stepping motor is driven by one step angle. If the value indicates the inhibited period, the system waits until the timer T value indicates the reception period. When the reception period comes, the stepping motor is driven by one step angle. As described previously, in a stepping motor drive control system according to the present invention, a step drive command is applied sequentially at irregular intervals to drive a stepping motor. With the step drive command applied, the stepping motor is driven by one step angle. According to the response characteristic of the stepping motor, an inhibited period when the execution of the next step drive command is inhibited and a reception period when the execution is enabled are set up. If the next step drive command is applied during the inhibited period, the system waits for the reception period. Then, the stepping motor is driven by one step angle. Therefore, the subsequent step drive operation can be performed at a good drive timing of the stepping motor. This helps stabilize the operation of the stepping motor. Thus, noise or vibrations of the stepping motor can be avoided.

Claims: A stepping motor drive control system for facsimile systems, comprising: a stepping motor (4) for transporting sheets; a motor driver (3) which controls switch-over of exciting current for said stepping motor (4) in accordance with step drive commands; first control means (1) for generating a start signal which starts a facsimile communication and said step drive commands, said first control means generating said step drive commands at irregular intervals; and characterised by second control means (2) for receiving said step drive commands from said first control means (1), said second control means (2) determining if the time elapsed after a switch-over operation in response to a previous step drive command is within a reception period when it receives a second or subsequent step drive command, enabling said motor driver (3) to perform a switch-over operation during the reception period, and inhibiting said motor driver (3) from performing a switch-over operation during an inhibited period distinct of said reception period. A stepping motor drive control system for facsimile systems according to claim 1, wherein the reception period when said second control means (2) enables said motor driver (3) and the inhibited period when the motor driver (3) is inhibited are determined such that the operation of said stepping motor (4) is stable during the reception period and the operation of said stepping motor (4) is unstable during the inhibited period. A stepping motor drive control system for facsimile systems according to claim 2, wherein the reception and inhibited periods for said second control means (2) are set by a timer (T₂; T). A stepping motor drive control system for facsimile systems according to claim 1, wherein said second control means (2) has first and second timers (T₁, T₂), the first timer (T₁) sets a given time required for a step control operation and the second timer (T₂) sets the reception and inhibited periods, and said second timer (T₂) is actuated after said first timer (T₁). A stepping motor drive control system for facsimile systems according to claim 4, wherein the first and second timers (T₁, T₂) are initialized with a start signal, and said second timer (T₂) is set to a minimum response time. A stepping motor drive control system, comprising: a stepping motor (4); a motor driver (3) which controls switch-over of exciting current for said stepping motor (4) in accordance with step drive commands; first control means (1) which generates a start signal and said step drive commands, said first control means generating said step drive commands at irregular intervals; and characterised by second control means (2) which receives said step drive commands from said first control means (1); said second control means (2) determining if the time elapsed after a switch-over operation in response to a previous step drive command is within a reception period or an inhibited period when it receives a second or subsequent step drive command, inhibiting said motor driver (3) to perform a switch-over operation during said inhibited period, making said motor driver wait until the reception period comes, and enabling said motor driver to perform the switch-over operation during the reception period.

Inventors: KATAOKA JUNNOSUKE, KATAOKA, JUNNOSUKE
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H02P8
IPC codes: H02P8