JPS6292797A - Control method for drive of stepping motor - Google Patents

Abstract

PURPOSE:To attain precise speed control by conducting open-loop control on starting and performing closed-loop control after an entering within a predetermined revolution range. CONSTITUTION:On starting, a changeover switch 34 is connected to the terminal 34a side, and a reference clock signal is brought to the state in which it is transmitted over an address counter 40. Consequently, the revolution of a stepping motor 12 is controlled under open-loop control. When the speed of rotation detected by a rotary encoder 30 reaches the predetermined speed of rotation, the switch 34 is changed over to the terminal 34b side by an output from a digital frequency comparator 32, and a closed loop control system using the rotary encoder 30 as a rotational speed detector is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stepping motor drive control method for controlling the stepping motor by microstep drive or sine wave drive.

The operation of a stepping motor is divided into two types: intermittent operation for position control and continuous operation for speed control. Among these, in the latter continuous operation, there is a disadvantage that speed unevenness occurs unless the step gap is finely provided. Therefore, in order to avoid the occurrence of this speed unevenness, methods such as (A) microstep drive (B) sine wave drive are adopted.

However, even if the stepping motor is continuously driven by the methods (A) and (B) above, the speed is actually controlled in an open loop, so it is free from the inconvenience of uneven rotation when load fluctuations occur. I can't do that.

Further, the general closed-loop control of a stepping motor using a lead angle is aimed at increasing torque to prevent step-out, and there is a problem in that it cannot be expected to reduce rotational unevenness.

Therefore, for example, when this type of motor is incorporated into a scanning device and the scanning device attempts to read image information, the movement of the record carrier in the sub-scanning direction is no longer constant, resulting in pitch unevenness of the scanning lines, which causes the reading to be difficult. Distortion or the like occurs in the image information to be read, resulting in the inconvenience that accurate and precise image information cannot be obtained.

For example, the present applicant utilizes a stimulable phosphor sheet and irradiates the radiation image of the subject stored and recorded on the stimulable phosphor sheet with excitation light. We have developed a radiation image reading device that emits light and uses a photoelectric element to read the stimulated emitted light and obtain it as an electrical signal for use in various diagnoses, and have filed a patent application. Here, a storage phosphor is a type of phosphor that is exposed to radiation (X-rays, α-rays, β-rays, T-rays, etc.).
When irradiated with ultraviolet rays, electron beams, etc., a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor changes depending on the accumulated energy. A stimulable phosphor that performs stimulated luminescence, and a stimulable phosphor formed into a sheet is called a stimulable phosphor sheet.

In the radiation image reading device, this stimulable phosphor sheet is transported at a constant speed via a transport device, and during this time, excitation light is deflected and irradiated onto the stimulable phosphor sheet one-dimensionally in a direction perpendicular to the transport direction. However, a system has been adopted that photoelectrically reads the stimulated luminescence light obtained thereby and electrically extracts radiation image information. In other words, a stimulable phosphor sheet (record carrier) is scanned two-dimensionally with a light beam (reading medium) such as a laser beam, and this spontaneously emitted stimulated luminescent light is detected by a photodetector such as a photomultiplier. Image information is obtained by sequential detection.

Therefore, two-dimensional scanning of the light beam is usually carried out by mechanically transporting the stimulable phosphor sheet in one direction, thereby performing sub-scanning, and at the same time directing the light beam in a direction perpendicular to the direction in which the sheet is transported. This is performed by performing main scanning with one-dimensional deflection.

When attempting to read image information from a stimulable phosphor sheet by performing two-dimensional scanning in this manner, it is preferable to transport the stimulable phosphor sheet in one direction at a stable speed.

In other words, if the sheet is not transported at a constant speed with high precision,
This is because uneven reading of image information occurs, and the final visible image used for observation and interpretation is inevitably an image whose observation and interpretation are degraded.

However, if the motor driving method according to the prior art is followed, as described above, the movement of the record carrier, that is, the stimulable phosphor sheet, in the sub-scanning direction is not always constant, and therefore, after reading There is an inconvenience in that it is impossible to avoid the occurrence of pitch unevenness in the image information G of the scanning lines.

The present invention has been made to overcome the above-mentioned disadvantages, and an object of the present invention is to provide a stepping motor drive control method that reduces rotational unevenness during constant speed rotation when the stepping motor is operated continuously. .

In order to achieve the above object, the present invention detects the rotation speed of a stepping motor in microstep drive or sine wave drive of the stepping motor, and detects the rotation speed when the detected rotation speed falls within a predetermined range with respect to a specified speed. closed-loop control that changes the drive signal frequency supplied to the stepping motor in a direction in which the deviation becomes zero in response to the deviation between the specified setting speed and the detected rotational speed from the time of the judgment. It is characterized by doing.

Next, a preferred embodiment of the stepping motor drive control method according to the present invention in relation to an image reading device for a stimulable phosphor sheet incorporating the stepping motor will be listed, and will be described below with reference to the accompanying drawings. Explain in detail.

Therefore, reference numeral 10 indicates a stimulable phosphor sheet as a record carrier storing radiation images, and a light beam such as a He-Ne laser as a reading medium is irradiated onto this stimulable phosphor sheet 10. This generates stimulated luminescence light on the sheet 10, and by reading this photoelectrically, radiation image information is obtained. That is, the stimulable phosphor sheet 10 is conveyed in the sub-scanning direction indicated by arrow A by a roller 14 that is rotationally driven by a stepping motor 12. The roller 14 is, for example, a suction roller, and is connected to a suction device (not shown). Therefore, air is sucked from the outer periphery of the roller 14 toward the center to prevent the stimulable phosphor sheet 10 being conveyed from slipping and to position it.

On the other hand, reference symbol 6 indicates an excitation light generating light source, which is preferably composed of a He-Ne laser, and the laser light from the He-NQ laser 16 is scanned in the main scanning direction shown by arrow B. It is configured to irradiate the galvanometer mirror 18 that is to be used. The galvanometer mirror 18 is rotationally driven by the output of the sawtooth wave generation circuit 20, and supplies the output of the frequency divider 22 to the sawtooth wave generation circuit 20 as a trigger signal to control the generation timing of the sawtooth wave output. It consists of

Note that the light collecting body 24 that collects the stimulated luminescent light emitted from the stimulable phosphor sheet 10 excited by the laser beam from the galvanometer mirror 18 has an incident surface 24a for light collecting on the stimulable phosphor sheet 10. It is provided facing the scanning line 26 on the IO, and the light collected by this condenser 24 is amplified by a photomultiplier tube 28 and then, for example, by a CR (not shown).
Output to T, etc. In the figure, reference numeral 30 indicates a rotary encoder connected to the rotational drive shaft of the stepping motor 12.

Next, a drive control circuit for the stepping motor 12 is shown in FIG. 2, and will be described in detail.

The output signal from a reference clock signal generator (not shown) is branched, one of which is introduced into the digital frequency comparator 32, and the other is connected to one terminal 34a of the changeover switch means 34. The output side of the digital frequency comparator 32 is connected to a voltage/frequency converter 38 (hereinafter referred to as a V/F converter) via a low-pass filter 36, and this V/F
The output side of the converter 38 is connected to the other terminal 34b of the changeover switch means 34. The changeover switch means 34 is further connected to an address counter 40, and its output side is connected to a ROM 42 addressed by the address counter 40.

The output side of the ROM 42 is then connected to an amplifier 46 via a digital/analog signal converter (hereinafter referred to as a D/A converter) 44 . Note that the output side of the rotary encoder 30 is connected to a digital frequency comparator 32,
Further, the output of the comparator 32 is used for switching the terminals of the changeover switch means 34.

That is, in this embodiment, the reference clock signal is transmitted via the ROM 42 storing the amplitude data of the sine wave for each division time when one cycle period of the sine wave is divided at predetermined time intervals, and the changeover switch means 34. an address counter 40 that specifies a read address from the ROM 42 based on the counted value; and a D/A converter 44 that converts the data read from the ROM 42 into an analog signal.
A variable frequency generator 50 is provided. In other words, by changing the frequency of the read signal from the ROM 42, the frequency of the sine wave signal generated by the variable frequency generator 50 changes.

The apparatus for carrying out the method of the present invention is basically constructed as described above, and its operation and effects will be explained next.

Therefore, at startup, the changeover switch means 34 is switched from the state shown in FIG. 2 and is connected to the terminal 34a side, so that the reference clock signal is supplied to the address counter 40. Therefore, the data read address address of the ROM 42 is incremented by "+1" at the cycle of the reference clock signal, and the rotation of the stepping motor 12 is controlled under open loop control.

By starting in this state, the stepping motor 12
When the rotational speed of the rotary encoder 30 increases and the rotational speed detected by the low-resolution encoder 30 reaches a rotational speed corresponding to the reference clock signal frequency, the output of the digital frequency comparator 32 causes the changeover switch means 34 to switch to the rotational speed shown in FIG. The position is switched to the position shown in , that is, to the terminal 34b side, and a closed loop control system using the low-return encoder 30 as a rotational speed detector is configured.

During this time, the output of the rotary encoder 30 is supplied to the digital frequency comparator 32, and the output of the rotary encoder 30 is supplied to the digital frequency comparator 32.
A frequency comparison is made between the output frequency and the reference clock frequency.

That is, the frequency comparison output from the digital frequency comparator 32 is supplied to a low-pass filter 36 to cut off high-frequency components of the frequency comparison output, and then supplied to the V/F converter 38 to be converted into a frequency signal. Therefore, by switching the changeover switch means 34 to the terminal 34b, the ROM
42 data are sequentially read out at the output frequency of the V/F converter 38 and converted into analog signals by the D/A converter 44. As a result, the output of the variable frequency generator 50 is amplified by the amplifier 46 and drives the stepping motor 12 in a sine wave. Therefore, it is easily understood that the frequency of the drive current that drives the stepping motor 12 corresponds to the output frequency from the V/F converter 38.

Therefore, when the rotation speed of the stepping motor 12 is slow, the drive current frequency of the stepping motor 12 is increased, while when the rotation speed of the stepping motor 12 is high, the drive current frequency is decreased. That is,
The rotational speed of the stepping motor 12 operates to be a constant rotational speed corresponding to the reference clock signal frequency.

In this embodiment, the reference clock signal frequency is described as being constant, but it goes without saying that the reference clock signal frequency may be changed sequentially.

As explained above, according to the present invention, when the stepping motor is started, open-loop control is performed, and when the rotational speed of the stepping motor enters a predetermined rotational speed range, closed-loop control is performed to increase the rotational speed of the stepping motor. It will be controlled to be constant. Therefore, precise speed control in the stepping motor is achieved, and recording unevenness or reading unevenness is avoided, especially in the case of a scanning system that uses a stimulable phosphor sheet to record or read radiation image information. A suitable effect can be obtained.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
Of course, various improvements and changes in design are possible without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of a radiation image reading device using a stimulable phosphor sheet, and FIG. 2 is a block diagram of an embodiment to which the method of the present invention is applied. 12...Stepping motor 30...Rotary encoder 32...Digital frequency comparator 34...Switching means 36...Low pass filter 38...V/
F Variable tAR340...Address counter 42
...ROM44...D/A converter 46.
...Amplifier 50...Variable frequency generator

Claims (1)

[Claims] (1) In microstep drive or sine wave drive of a stepping motor, the rotational speed of the stepping motor is detected, it is determined that the detected rotational speed is within a predetermined range with respect to the set specified speed, and the above-mentioned determination is performed. The stepping motor is characterized in that a closed-loop control is performed in which a drive signal frequency supplied to the stepping motor is changed from time to time in a direction in which the deviation becomes zero in response to a deviation between the set specified speed and the detected rotational speed. Drive control method.