Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
1999-05-11
2001-08-14
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
Reexamination Certificate
active
06274996
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a drive control method for a stepping motor used for driving a printing head, and more particularly a drive control method for a stepping motor driver of the slow-decay type.
There is proposed a method for driving and controlling a printing head of a printer by use of a slow-decay type of a stepping motor.
A drive circuit for the stepping motor is of the bipolar type in which to efficiently use the coils, each motor phase is operated by use of a bridge circuit and the polarity of the motor phase is alternately inverted by flowing bipolar current thereto.
FIGS. 8 and 9
show a drive circuit for driving a slow-decay type of a stepping motor. As shown, a bridge circuit is formed by use of four diodes D
1
to D
4
. Switching transistors Q
1
to Q
4
are coupled across those diodes, respectively. To set up a chopping mode in the bridge circuit, switching transistors Q
1
and Q
4
are turned on, and current flows through a current path including a coil L (FIG.
8
). To remove the chopping mode, the switching transistor Q
4
remains on, and the switching transistor Q
1
is turned off. As a result, current supply to the coil L is stopped. At this time, the coil L generates an electromotive force because of electromagnetic nature thereof, so that current flows through the coil L, the switching transistor Q
4
, and the diode D
2
in this order (FIG.
9
). As a result, the current flowing through the coil L is gradually attenuated. The same thing is true for a case where the coil L is energized by the transistors Q
2
and Q
3
.
The conventional drive circuit for the stepping motor of the slow-decay type uses a W1-2 phase driving method (as shown in
FIG. 7
) for the motor speed control in all acceleration, constant-speed and deceleration states or conditions.
In
FIG. 7
, a signal PH
1
is a signal indicative of a polarity of current flowing through a first phase coil; signals I
01
and I
11
are step pulses for controlling the current flowing through the first phase coil; a signal OUT
1
is a current output to the first phase coil; a signal PH
2
is a signal indicative of a polarity of current flowing through the second phase coil; signals I
01
and I
12
are step pulses for controlling the current flowing through the second phase coil; and a signal OUT
2
is a current output to the second phase coil. The current waveforms indicated by solid lines shown in OUT
1
and OUT
2
in
FIG. 7
are logic waveforms, and their actual waveforms are as indicated by dashed lines.
The waveform of the current signal OUT
1
is configured in four steps by combinations of signal states “H” and “L” of two step pulse signals I
01
and I
11
. Namely, when both of I
01
and I
11
are “H”, OUT
1
becomes 0%. When I
01
is “L” and I
11
is “H”, it becomes 33% (or −33%). When I
01
is “H” and I
11
is “L”, it becomes 66% (or −66%). When both of I
01
and I
11
becomes “L”, it becomes 100%. The above combination relationships are correspondingly applied to the combination relationships between the current signal OUT
2
flowing into the second phase and the two pulse signals I
01
and I
02
for controlling it.
As seen from the above description, in the W1-2 phase driving method, when current is supplied to the first phase coil, the output current signal OUT
1
is gradually increased (in four steps) up to 100% (or −100%). When current supply to the first phase coil is stopped, the output current signal OUT
1
is gradually decreased (in four steps) up to 0%.
More specifically, during a time period from a time point t
1
(at which current supply to the first phase coil starts) to a time point t
2
, the pulse signal I
01
is set at “H” and the pulse signal I
11
is set at “H”, and the output current signal OUT
1
is 0%. During the succeeding time period from t
2
to t
3
, the pulse signal I
01
is “L” and the pulse signal I
11
is “H”, and the output current signal OUT
1
is 33%. During the succeeding time period from t
3
to t
4
, the pulse signal I
01
is “H” and the pulse signal Ill is “L”, and the output current signal OUT
1
is 66%. During the succeeding time period from t
5
to t
6
, the pulse signal I
01
is “L” and the pulse signal I
11
is “L”, and hence the output current signal OUT
1
is 100%. Thus, the output current signal OUT
1
is gradually increased from 0% to 100% during a time period from t
1
to t
4
.
During a time period from time points t
4
to t
7
, the output current signal OUT
1
is kept at 100%. During a time period from t
7
to t
8
, the pulse signal I
01
is “H” and the pulse signal Ill is “L”, and then the output current signal OUT
1
is 66%. During a time period from t
8
to t
9
, the pulse signal I
01
is “L” and the pulse signal I
11
is “H”, and hence the output current signal OUT
1
is 33%. During a time period from t
9
to t
10
, the pulse signal I
01
is “L” and the pulse signal I
11
is “L”, so that the output current signal OUT
1
is 0%. Thus, during a time period from t
7
to t
10
, the output current signal OUT
1
is gradually decreased from 100% to 0%.
Similarly, when current is also fed to the second phase coil, the output current signal OUT
2
is gradually increased (in four steps) to 100% (or −100%). Also when current feeding to the second phase coil is stopped, the output current signal OUT
2
is gradually decreased (in four steps) to 0%.
In case where the W1-2 phase driving method is used for the speed control of the printing head, drive sound and vibrations are diminished in particular when the printing head is accelerated (driven to start its movement) and decelerated (stopped).
In case where the W1-2 phase driving mode is performed in the constant-speed state where the printing is carried out by the printing head, the current control fails when the drive circuit for the slow-decay type stepping motor is operated in a microstep driving mode, in particular when the current is attenuated. Comparing an actual waveform (depicted by dashed lines) of the output current signal OUT
1
(OUT
2
) with a logic waveform (depicted by solid lines) of the same in their amplitude decreasing portions. As seen from the comparison, the actual waveform more gently decreases its amplitude than the logic waveform, and after a short time, its amplitude abruptly decreases to 0% while the logic waveform stepwise decreases its amplitude. This output current variation will causes printing head vibrations and vertical stripes which appear in the printed picture or print while being spaced at fixed intervals. Those vertical stripes are a little distinguished in normal print; however, those are likely to occur and becomes problematic in high definition print.
To solve the stripe problem, there is a proposal of a drive control method for a stepping motor (referred frequently to as a motor drive control method), disclosed in Unexamined Japanese Patent Publication No. 5-278293. In the motor drive control method, in acceleration and deceleration states or conditions, the motor speed control progresses selectively using the 1-2 phase driving mode and the 2-2 phase driving mode. More precisely, in low speed states, the 1-2 phase driving mode is used which less produces vibrations and noisy sounds (drive sound). In high speed states, the 2-2 phase driving mode is used which requires a small number of motor-drive switching.
The conventional motor drive control method succeeds in suppressing generation of vertical stripes in a satisfactory level in normal print. However, it has still such a problem that a definition of the print is unsatisfactory in high definition print.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made to solve the above problems, and has an object to provide a drive control method for a stepping motor which improves a definition of the print, and completely suppresses vibrations and drive sounds of the motor by completely eliminating generation of the stripes in the printed picture.
In order to achieve the above object, there is provided a drive control apparatus for a stepping motor compri
Funai Electric Co. Ltd.
Lackenbach Siegel Marzullo Aronson & Greenspan P.C.
Ro Bentsu
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