Stepping motor control having a dynamically variable loop filter circuit
First Claim
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1. A stepping motor control circuit for starting and maintaining a desired motor operating speed comprising in combination:
- a voltage controlled oscillator;
a phase comparator;
means for providing a motor speed signal;
means for providing a desired speed signal;
said motor and desired speed signal means being connected to the input of said phase comparator;
a main loop filter;
a boot strap loop filter;
said main and bootstrap loop filters being connected in parallel in operative relation with said comparator and said voltage controlled oscillator; and
means for gradually removing the bootstrap loop filter effect from the circuit as the stepping motor approaches operating speed.
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Accused Products
Abstract
Apparatus for controlling a stepping motor drive system during start up and maintenance of a desired oeprating speed. A dynamically variable loop filter i.e. a boot strap loop filter is used in a phase locked loop circuit to ramp the stepping motor to operative speed faster and with less transient instability than heretofore available. Protection from transients tending to cause slower or faster speeds is obtained with the same circuits. Stall sensing and restart capabilities are provided and the circuits use fewer components and less PCB real estate than prior art.
17 Citations
15 Claims
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1. A stepping motor control circuit for starting and maintaining a desired motor operating speed comprising in combination:
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a voltage controlled oscillator; a phase comparator; means for providing a motor speed signal; means for providing a desired speed signal; said motor and desired speed signal means being connected to the input of said phase comparator;
a main loop filter;
a boot strap loop filter;said main and bootstrap loop filters being connected in parallel in operative relation with said comparator and said voltage controlled oscillator; and means for gradually removing the bootstrap loop filter effect from the circuit as the stepping motor approaches operating speed. - View Dependent Claims (2)
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3. In a color video system of the type having a motor driven color video wheel, apparatus for synchronizing the color video wheel with the video field rate of the system that includes:
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a rotatably mounted color filter wheel having a series of different color filters that are passed in sequence through a fixed optical axis as the wheel is rotated; a stepping motor operatively connected to said color wheel for rotation thereof; a color wheel drive circuit operatively connected to said stepping motor for rotating said motor in response to an input stepping signal applied thereto; a second order phase locked loop filter circuit connected to said drive circuit; said second order phase locked loop filter circuit further including a phase comparator, a voltage controlled oscillator, a main loop filter and a bootstrap loop filter; said bootstrap loop filter being operatively connected with said main loop filter to form an RC network having a dynamically changing time constant; means to effectively remove said bootstrap loop filter from the circuit when the stepping motor approaches operating speed; and a timing pin and optical sensor for indicating color wheel position and speed. - View Dependent Claims (4)
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5. In a color video system of the type having a rotatably mounted color filter wheel having a series of different color filters that are passed in sequence through a fixed optical axis as the wheel is rotated;
- and a stepping motor operatively connected to said color wheel for rotation thereof;
apparatus for synchronizing the color video wheel with the video field rate of the system that includes;a color wheel drive circuit including a stepping motor encoder and driver circuit connected to the stepping motor; a voltage controlled oscillator circuit connected to the input of said encoder and driver circuit; a dynamically variable loop filter circuit connected to the input of said voltage controlled oscillator; a timing pin operatively connected to rotate with said color wheel; an optical sensor circuit for sensing the rotation of said pin; and a phase comparator circuit for comparing the output signal from said optical sensor and a field index signal from the video system connected to the input to said dynamically variable loop filter circuit. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
- and a stepping motor operatively connected to said color wheel for rotation thereof;
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14. A method of controlling the rotational speed of a color filter wheel in a video system that includes the steps of:
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driving a color filter wheel with a stepping motor to sequentially advance different color filters past a fixed optical axis; applying the output of a voltage controlled oscillator to the input of said stepping motor; deriving a control voltage for said voltage controlled oscillator by comparing a timing pulse from said color wheel and a field index signal from a video system; applying said control voltage to a dynamically variable loop filter circuit before applying it to the input of said voltage controlled oscillator; limiting the magnitude of said control voltage by adjusting the time constant of the dynamically variable loop filter circuit to a level suitable for ramping the stepping motor up to operating speed; and varying the time constant of said dynamically variable loop filter circuit proportional to the difference between desired and actual motor speed.
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15. A method of controlling the rotational speed of a color filter wheel in a video system that includes the steps of:
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driving a color filter wheel with a stepping motor to sequentially advance different color filters past a fixed optical axis; applying the output of a voltage controlled oscillator to the input of said stepping motor; deriving a control voltage for said voltage controlled oscillator by comparing a timing pulse from said color wheel and a field index signal from a video system; applying said control voltage to a variable loop filter circuit; dynamically varying the time constant of said variable loop filter circuit as the stepping motor changes speed; and applying the output of said variable loop filter circuit to said voltage controlled oscillator; whereby said stepping motor is rapidly ramped up to stable synchronous operating speed.
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Specification