Step motor driving device

Details Step motor driving device Step motor driving device

1999-12-30

2001-08-07

Ro, Bentsu (Department: 2837)

Electricity: motive power systems

Positional servo systems

With particular motor control system responsive to the...

C318S696000, C318S671000, C318S714000, C318S567000

Reexamination Certificate

active

06271641

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel step motor driving device which drives a step motor free from jumping out of synchronism
BACKGROUND OF THE INVENTION
Step motors have been recently used in numbers of office automation apparatuses and computer peripherals such as printers, facsimile machines, image scanners, copying machines, laser beam printers and the like, as well as factory automation equipment including machine tools. The step motors are thus now extensively used both in applications and quantity, because an extremely simple and extraordinarily inexpensive system employing a step motor can perform a speed control or a positioning control.
FIG.
73
A and
FIG. 73B
illustrate a construction and a circuit diagram of a conventional step-motor-driving device in accordance with a first conventional instance.
In
FIG. 73A
, two-phase step motor
801
includes two-phase driving windings, which are hereinafter referred to as phase-A winding and phase-B winding. Exciters
802
a
and
802
b
receive driving-instruction-signals DrA, DrB, thereby exciting phase-A winding and phase-B winding.
As shown in
FIG. 73B
, exciter
802
a
comprises a bridge circuit formed by four transistors, and this circuit works as follows: When input IN-A is at H level, output A takes H level and output /A takes L level. When input IN-A is at L level, output A takes L level and output /A takes H level. In other words, when input IN-A is at H level, a voltage VDC of dc current (not shown) allows the current to flow in plus direction, i.e. flowing from A to /A. When input IN-A is at L level, the voltage VDC allows the current to flow in minus direction, i.e. from /A to A. Another exciter
802
b
is identical to exciter
802
a
both in construction and operation.
On-delay circuits
811
-
814
(Dly) are provided as shown in
FIG. 73B
in order to prevent the transistor switches—making up the bridge circuit—from shorting the power supply by an error.
In
FIGS. 73A and 73B
, a plus voltage VDC is applied between inputs A and /A of exciter
802
a
when signal DrA is at H level. This voltage excites phase-A winding to be plus. On the other hand, a minus voltage VDC is applied between inputs A and /A when signal DrA is at L level, and this voltage excites phase-A winding to be minus. Phase-B winding excited by exciter
802
b
experiences the same phenomena as discussed above.
FIGS. 74A-74D
illustrate an operation of the conventional motor driving device employed in the first conventional instance.
FIG. 74A
illustrates relation between mover's position &thgr; and torque T generated there, where torque T is obtained by providing the driving windings of motor
801
with a given excitation. The relations between position &thgr; and torque T in respective instances are expressed in
FIG. 74A
as follows:
Ta: phase-A winding is excited to be plus;
Th: phase-B winding is excited to be plus;
−Ta: phase-A winding is excited to be minus; and
−Tb: phase-B winding is excited to be minus.
When the mover travels in positive direction, mover's position &thgr; corresponds to the rightward direction in
FIG. 74A
, and when the mover travels in negative direction, it corresponds to the leftward direction in FIG.
74
A. Regarding torque T, a forward direction allows the mover to travel in the positive direction and a reverse direction allows the mover to travel in the negative direction. The torque in the forward direction heads upper side of FIG.
74
A.
In
FIG. 74A
, a torque generated by exciting the phase-A winding has a difference of 90-degree electrical angle from a torque generated by exciting the phase-B winding. Because driving windings of respective phases are mounted with a shift of 90-degree electrical angle with regard to polarity pitch of the mover.
FIG. 74B
illustrates a relation between mover's position &thgr; and torque T generated there by exciting both phase-A and phase-B windings (2-phase exciting drive). The relations between &thgr; and T in respective instances in
FIG. 74B
are expressed as follows:
Ta+Th: phase-A and phase-B windings are excited to be plus;
−Ta+Tb: phase-A winding is excited to be minus and phase-B winding is excited to be plus;
−Ta−Tb: phase-A and phase-B windings are excited to be minus; and
Ta−Tb: phase-A winding is excited to be plus and phase-B winding is excited to be minus.
Each instance discussed above is a composite of each torque shown in FIG.
74
A. Regarding mover's position &thgr; and the direction of torque,
FIG. 74B
expresses them in the same manner as
FIG. 74A
does.
According to the above description regarding the step motor, it is roughly concluded that a relation between mover's position &thgr; and torque T generated there can be uniquely determined when the driving windings of respective phases are excited to a given level.
FIG. 74C
illustrates driving instruction signals DrA, DrB are fed, with 90 degree out of phase, into exciter
802
a
and
802
b
, and
FIG. 74D
illustrates how motor
801
works with these driving instructions.
Before time t
1
, since signals DrA, DrB are at H level, both phase-A and phase-B windings are excited to be plus, and torque “Ta+Th” drives the mover during this plus period. At time t
1
, when signal DrA changes from H level to L level, the polarity of exciting phase-A winding changes so that torque changes to be expressed “−Ta+Tb” and turns to the forward direction again. Due to these changes, the mover is further driven in the same (positive) direction until time t
2
when signal DrB changes from H level to L level.
At time t
2
, when signal DrB changes from H level to L level, the polarity of exciting phase-B winding changes so that torque changes to be expressed “−Ta−Tb” and turns to the forward direction again. The mover is then further driven in the same (positive) direction without pause.
In the same manner, at time t
3
, t
4
and t
5
, whenever signals DrA, DrB change, the polarities of exciting phase-A and phase-B windings alternately change so that torque changes to be expressed “Ta−Tb”, “Ta+Tb”, and “−Ta+Tb” and turns to the forward direction sequentially. The mover is thus kept driving in the same (positive) direction.
The first conventional step motor driving device operates as discussed above. In this first conventional instance, when the frequencies of signals DrA, DrB increase, the torque for driving the mover of the motor lowers so quick that the mover loses speed. As a result, the motor jumps out of synchronism.
There are two major factors for the motor to jump out of synchronism:
1. Inductance of driving windings affects the current to be insufficient for exciting the windings so that a desirable torque cannot be generated. Several methods have been proposed to overcome this factor. For example, a method of putting a series resistor in order to reduce electrical time constant of the windings, and a method of boosting a driving voltage temporarily to establish an exciting current quickly, were proposed. Another method is disclosed in the Japanese Patent Application Examined Publication No. S41-9489, i.e. a driving voltage is changed responsive to a frequency of a driving instruction signal.
2. A switch timing of exciting the windings is off the relation between the mover's position &thgr; determined by excitation of the windings and torque T generated there. This second factor is described hereinafter with reference to
FIGS. 75A-75D
.
FIGS. 75A and 75B
illustrate relations between the mover's position &thgr; and torque T generated there when the windings of respective phases are excited. Those FIGS. are identical to
FIGS. 74A and 74B
.
Assume that driving instruction signals DrA, DrB, of which frequencies are higher than those shown in
FIG. 74C
, are fed to be exciting signals IN-A and IN-B into exciters as shown in FIG.
75
C.
Signals DrA, DrB switch the direction of respective excitations applied to the driving windings, thereby generating a torque as i

Affiliated with

Also associated with

Rating

Step motor driving device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Step motor driving device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Step motor driving device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2492647