Method and circuit for controlling an electromagnetic actuator in photographic apparatus
First Claim
1. In photographic apparatus having an electromagnetic actuator of the type including an armature mounted for movement between a rest position and an extreme position in a magnetic field and means for urging the armature toward the rest position, a control circuit comprising:
- means for applying a first polarity voltage pulse to said armature of duration effective for moving said armature against the force of said urging means to a programmed position between said rest position and said extreme position; and
means for applying an opposite polarity voltage pulse to said armature of duration effective for braking said armature at said programmed position.
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Accused Products
Abstract
An improved control circuit for an electromagnetic actuator of the type having an armature mounted for movement in a magnetic field, and means connected to the armature for urging the armature toward a rest position. The circuit applies an electrical pulse of a first polarity, magnitude and duration to the armature to quickly move the armature to a programmed position determined by the magnitude and duration of said pulse, the programmed position lying within a range of positions between said rest position, and an extreme position achievable by the armature. The control circuit then applies a pulse of opposite polarity and of magnitude and duration effective to stop the armature at the programmed position. The control circuit applies a periodic train of pulses of said first polarity, of fixed magnitude and of duration, effective to hold the actuator in the programmed position, the period of said train of pulses being above the natural cutoff frequency of the actuator. To quickly return the armature to the rest position, the control circuit applies a pulse of opposite polarity and of duration and magnitude effective to the armature to move the armature in cooperation with the urging means, to the rest position. The circuit then applies a braking pulse of said first polarity and of duration and magnitude effective to stop the armature at the rest position.
In a preferred embodiment, the actuator controls a shutter/aperture in a camera, the duty cycle (i.e. pulse duration) of the train of pulses determines the aperture size, and the number of pulses in the pulse train determines the shutter time. The control circuit also includes means for boosting the voltage of the moving and braking pulses to achieve extremely short shutter times.
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Citations
23 Claims
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1. In photographic apparatus having an electromagnetic actuator of the type including an armature mounted for movement between a rest position and an extreme position in a magnetic field and means for urging the armature toward the rest position, a control circuit comprising:
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means for applying a first polarity voltage pulse to said armature of duration effective for moving said armature against the force of said urging means to a programmed position between said rest position and said extreme position; and means for applying an opposite polarity voltage pulse to said armature of duration effective for braking said armature at said programmed position. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In photographic apparatus having an electromagnetic actuator of the type including an armature with an electrical conductor, means for producing a magnetic field in the vicinity of the armature, means for mounting the armature for relative movement with respect to the field producing means between a rest position and an extreme position in response to an electrical current in the conductor, and urging means connected to the armature for urging the armature toward the rest position, an improved actuator control circuit comprising:
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means for applying a series of 50 percent duty cycle positive and negative voltage "leader" pulses to said conductor, the frequency of said "leader" pulses being above the cutoff frequency of said actuator, for overcoming the static friction of said actuator; means for applying a positive voltage pulse to said conductor of duration effective for moving said armature against the force of said urging means to a programmed position away from said rest position; means for applying a negative voltage pulse to said conductor of duration effective for braking said armature at said programmed position; means for applying a negative pulse to said conductor of duration effective for moving said armature in cooperation with said urging means to said rest position; and means for applying a positive pulse to said conductor of duration effective for braking said armature at said rest position. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method of controlling an electromagnetic actuator of the type having an armature including an electrical conductor, means for producing a magnetic field in the vicinity of the armature, means for mounting the armature for relative movement with respect to the field producing means between a rest position and an extreme position in response to an electrical current in the armature, and urging means connected to the armature for urging the armature toward the rest position, said method comprising the steps of:
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applying a series of 50 percent duty cycle positive and negative voltage "leader" pulses to said conductor, the frequency of said leader pulses being above the cutoff frequency of said actuator, for overcoming the static friction of said actuator; applying a positive voltage pulse to said conductor of duration effective for moving said armature against the force of said resilient means to a programmed position between said rest position and said extreme position; applying a negative pulse to said conductor of duration effective for braking said armature at said programmed position; applying a negative pulse to said conductor of duration effective for moving said armature in cooperation with said urging means to said rest position; and applying a positive pulse to said conductor of duration effective for braking said armature at said rest position. - View Dependent Claims (16, 17, 18, 19)
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20. In a photographic apparatus, a control circuit for an electromagnetic actuator of the type having an armature including an electrical conductor, means for producing a magnetic field in the vicinity of the armature, means for mounting the armature for relative movement with respect to the field producing means between a rest position and an extreme position in response to an electrical current in the conductor, and urging means connected to the armature for urging the armature toward a rest position, said control circuit comprising:
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a microcomputer, including a memory containing a control program, having first and second digital signal output lines; a first electrical power supply; and drive circuit means, including a high gain differential amplifier, connected to said microcomputer, to said power supply, and to said electromagnetic actuator for supplying electrical current to said armature under control of said microcomputer, said differential amplifier having a power input connected to said power supply, first and second differential inputs connected to said first and second digital output lines, and first and second complementary power outputs for connection to said actuator, said differential amplifier being responsive to a logical one on said first input and a logical zero on said second input for producing a positive voltage across said complementary outputs, responsive to a logical zero on said first input and a logical one on said second input for producing a negative voltage across said outputs, and responsive to a logical zero applied to both said first and second inputs for producing no voltage across said outputs, said microcomputer being programmed to cause said drive circuit means to produce across said complementary outputs;
(1) a series of 50 percent duty cycle positive and negative voltage "leader" pulses, the frequency of said leader pulses being above the cutoff frequency of said actuator, for overcoming the static friction of said actuator;
(2) a positive voltage pulse of duration effective for moving said armature against the force of said resilient means to a programmed position between said rest position and said extreme position;
(3) a negative voltage pulse of duration effective for braking said armature at said programmed position;
(4) a negative voltage pulse of duration effective for moving said armature in cooperation with said urging means to said rest position; and
(5) a positive voltage pulse of duration effective for braking said armature at said rest position. - View Dependent Claims (21, 22, 23)
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Specification