Lens controlling apparatus

Details Lens controlling apparatus Lens controlling apparatus

1996-07-09

2001-09-04

Martin, David S. (Department: 2837)

Electricity: motive power systems

Positional servo systems

With particular motor control system responsive to the...

C318S696000, C396S080000, C396S086000, C396S082000, C359S698000

Reexamination Certificate

active

06285154

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens controlling apparatus suitable for use in a still camera, a video camera or the like.
2. Description of the Related Art
It has heretofore been known that stepping motors are employed in many precision machines which require highly accurate position control.
Stepping motors are also employed in, for example, video cameras for the purpose of lens control. This is primarily because such a stepping motor can achieve a high positioning accuracy and can be controlled easily and at high speed because of its open-loop control.
FIG. 1
shows the arrangement and operation of a stepping motor. Referring to
FIG. 1
, the central magnetic poles constitute a rotor, while the peripheral magnetic poles constitute a stator. Each of the magnetic poles of the rotor is formed by a permanent magnet, while each of the magnetic poles of the stator is formed by the magnetization of the stator by the current supplied to the stepping motor.
In the stepping motor shown in
FIG. 1
, if the polarity of the stator is varied in the order of from (a) to (d), the rotor moves as indicated by the respective arrows:
(a) Magnetic poles A and -A become a south pole and a north pole, respectively, and magnetic poles B and -B have no polarities;
(b) The magnetic poles A and -A have no polarities, and the magnetic poles B and -B become a south pole and a north pole, respectively;
(c) The magnetic poles A and -A become a north pole and a south pole, respectively, and the magnetic poles B and -B have no polarities; and
(d) The magnetic poles A and -A have no polarities, and the magnetic poles B and -B become a north pole and a south pole, respectively.
As can be seen from
FIG. 1
, to rotate the stepping motor, it is only necessary to vary the polarity of the stator in the above-described manner.
In some existing stepping motor driving apparatus, to cope with the problem of noise or the like, the stator is magnetized by using a sinusoidal, driving current waveform such as shown in FIG.
2
. In the current waveform shown in
FIG. 2
, the positions indicated at (a) to (d) respectively correspond to the positions indicated by the arrows in FIG.
1
.
In the case where the stator is magnetized by using the driving current waveform shown in
FIG. 2
, if the stepping motor stops at a phase position other than the phases indicated by the respective arrows in
FIG. 1
, the relationship between the magnetic poles of the stator and those of the rotor becomes imperfect and the rotor becomes extremely unstable. As a result, the rotor moves by a particular magnetic pole of the rotor being attracted by either one of two adjacent magnetic poles of the stator opposite to the particular magnetic pole. For this reason, in the case of the driving current waveform shown in
FIG. 2
, the stepping motor must not be stopped at any phase position other than predetermined phases (the positions indicated by the respective arrows in
FIG. 1
, i.e., the positions indicated at (a) to (d) in FIG.
1
).
After the stepping motor has been stopped, to hold the stepping motor at that stop position, it is necessary to continue to supply current having a phase identical to the phase of the driving current waveform supplied to the stepping motor immediately before the stop of the stepping motor. The magnitude of the current may be far smaller than that of the driving current supplied during the driving of the stepping motor.
FIG. 3
diagrammatically shows one example of the stepping motor driving apparatus, and
FIG. 4
shows in detail the output current waveform of the driving apparatus of
FIG. 3
which corresponds to either one phase.
The driving apparatus shown in
FIG. 3
includes a control device
50
for performing control of the apparatus in which a stepping motor
52
is disposed, the control device
50
being formed by a microcomputer, and a motor driving device
51
for driving the stepping motor
52
on the basis of a control signal supplied from the control device
50
, as well as the stepping motor
52
. The internal arrangement of the motor driving device
51
will be described below. Input/output lines
501
to
505
are disposed between the control device
50
and the motor driving device
51
. The line
501
is a clock input line for inputting a clock signal to the motor driving device
51
, the line
502
is a driving-direction input line for inputting a driving-direction signal to the motor driving device
51
, the line
503
is a monitor output line for outputting a signal indicating that the phase of the motor driving circuit
14
is a predetermined phase, the line
504
is a stop instruction input line for inputting a stop instruction to the motor driving device
51
, and the line
505
is a power saving instruction input line for inputting a power saving instruction to decrease the amount of current to be supplied to the stepping motor
52
.
The motor driving device
51
includes a counter
511
for counting the number of clocks which are supplied from the control device
50
via the clock input line
501
, a current waveform forming circuit
512
for forming a current waveform in accordance with a count value provided by the counter
511
, a switch
513
disposed between the clock input line
501
and the counter
511
and operated via the stop instruction input line
504
, a constant current source
514
for supplying a constant current to the stepping motor
52
during a power saving operation, and a switch
515
for selecting current to be supplied to the stepping motor
52
by performing switching between the output of the current waveform forming circuit
512
and the output of the constant current source
514
. The switch
515
is operated via the power saving instruction input line
505
.
Clocks supplied via the clock input line
501
are counted by the counter
511
included in the motor driving device
51
, and a current value which is set by the current waveform forming circuit
512
advances step by step in accordance with the count value of the counter
511
, thereby forming a motor driving current waveform. A logic level supplied via the driving-direction input line
192
determines whether the stepping motor
52
is to be driven in the forward or backward direction.
Each time the current waveform reaches a predetermined phase, a low-level (L) signal is outputted to the monitor output line
503
as shown in FIG.
4
. If the stop instruction input line
504
goes to a high level (H), the switch
513
is opened to disconnect the clock input line
501
and the counter
511
from each other. Accordingly, even if a clock is inputted, the counting of the counter
511
does not advance any more so that the stepping motor
52
stops. If the level of the power saving instruction input line
505
is “H”, the output of the current waveform forming circuit
512
is connected to the stepping motor
52
, while if the level of the power saving instruction input line
512
is “L”, the output of the constant current source
514
is connected to the stepping motor
52
.
The control device
50
controls the motor driving device
51
in the following manner:
(1) When the stepping motor
52
is to be driven, the control device
50
sets a direction in which to drive stepping motor
52
via the driving-direction input line
502
. Then, the control device
50
inputs a clock signal to the clock input line
501
and causes the current waveform forming circuit
512
to output a motor driving current waveform, thereby driving the stepping motor
52
.
(2) When the stepping motor
52
is to be stopped, after the control device
50
confirms through the monitor output line
503
that the stepping motor
52
is positioned at any one of the predetermined phases, the control device
50
sets the level of the stop instruction input line
504
to “H”.
(3) When the direction of driving of the stepping motor
52
is to be changed, the control device
50
temporarily stops the stepping motor
52
in the manner stated above in the paragraph (2), and inverts the le

Affiliated with

Also associated with

Rating

Lens controlling apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2543422