Absolute position sensing by phase shift detection using a variable capacitor
First Claim
1. A capacitive position sensor comprising:
- a first stator and a second stator, each of said first and second stators coupled to a driver signal input to allow a driver signal to be input to said first and second stators;
a resistor coupled between said driver signal input and said first stator;
a vane, wherein said vane moves parallel to said first stator such that said vane overlaps at least a portion of said first stator, thereby creating a capacitance that varies as said vane moves;
a dielectric provided between said vane and said first stator; and
a circuit coupled to said first stator, said circuit sensing a voltage on said first stator based on relative positions of said first stator and said vane, said circuit providing a phase-shifted signal describing a phase shift of said voltage with reference to said driver signal, said phase shifted signal suitable for deriving an absolute position of said vane with respect to said first stator.
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Accused Products
Abstract
A low-cost, high-resolution capacitive position sensor is provided using a variable capacitor. A vane moves parallel to a stator, where a dielectric is interposed between vane and stator, such that the vane overlaps at least a portion of the stator, creating a capacitance that varies as the vane moves relative to the fixed stator. The capacitor circuit outputs a signal having a phase shift relative to an input driver signal based on the relative positions of the vane and stator. The phase-shifted signal is used to derive the absolute position of the vane with respect to the stator. Two or more stator can be provided to provide two phase-shifted signals and a difference signal free of common mode effects. Enhanced embodiments include interdigitated stator portions for greater sensing resolution, and/or a two or three-pole filter to double or triple the dynamic range of the sensor.
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Citations
31 Claims
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1. A capacitive position sensor comprising:
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a first stator and a second stator, each of said first and second stators coupled to a driver signal input to allow a driver signal to be input to said first and second stators;
a resistor coupled between said driver signal input and said first stator;
a vane, wherein said vane moves parallel to said first stator such that said vane overlaps at least a portion of said first stator, thereby creating a capacitance that varies as said vane moves;
a dielectric provided between said vane and said first stator; and
a circuit coupled to said first stator, said circuit sensing a voltage on said first stator based on relative positions of said first stator and said vane, said circuit providing a phase-shifted signal describing a phase shift of said voltage with reference to said driver signal, said phase shifted signal suitable for deriving an absolute position of said vane with respect to said first stator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. An interface device including a capacitive position sensor, said interface device being coupled to a host computer and providing input to said host computer based on manipulations of a user of said interface device to manipulate computer-generated objects, said interface device comprising:
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(a) a position sensor, including;
(i) a stator coupled to a driver signal input to allow a driver signal to be input to said stator;
(ii) a resistor coupled between said driver signal input and said stator;
(iii) a dielectric provided on one side of said stator;
(iv) a vane positioned such that said dielectric is between said stator and said vane, wherein said vane moves parallel to said stator such that said vane overlaps at least a portion of said stator, thereby creating a capacitance that varies as said vane moves; and
(v) a circuit coupled to said stator, said circuit sensing a voltage on said stator based on relative positions of said stator and said vane, said circuit outputting a signal describing a phase shift of said voltage with reference to said driver signal, wherein an absolute position of said vane with respect to said stator is derivable from said signal describing said phase shift; and
(b) a user manipulandum grasped and moved by a user in a degree of freedom, wherein said user manipulandum is coupled to said vane such that movement of said vane corresponds to movement of said user manipulandum in said degree of freedom. - View Dependent Claims (20, 21, 22, 23, 24)
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25. A method for sensing the position of a moving member, the method comprising:
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providing an input signal having a frequency;
shifting a phase of said input signal by inputting said input signal to a first RC circuit and to a second RC circuit to provide a first phase-shifted signal and a second phase-shifted signal, said first RC circuit including a resistor and a capacitor coupled in series, wherein said input signal is input to said resistor, and wherein said capacitor of said first RC circuit is a variable capacitor having two plates and having a capacitance based on a position of a first one of said plates with reference to a second one of said plates, wherein said relative positions of said plates are determined based on a position of said moving member; and
providing said first phase-shifted signal to a phase detector circuit, said phase detector circuit having a first input coupled at a node between said resistor and said capacitor to sense a voltage at said node and having a second input that is said input signal, said phase detector circuit outputting a pulse width modulated signal which is linearly proportional to the position of one of said plates with respect to the other of said plates. - View Dependent Claims (26, 27, 28, 29, 30)
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31. A capacitive position sensor comprising:
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a fixed conductive plate;
a movable conductive plate coupled to a driver signal input to allow a driver signal to be input to said movable conductive plate, wherein said movable conductive plate moves parallel to said fixed conductive plate such that said movable conductive plate overlaps at least a portion of said fixed conductive plate, thereby creating a capacitance that varies as said movable conductive plate moves;
a resistor coupled between said driver signal input and said movable conductive plate;
a dielectric provided between said movable conductive plate and said fixed conductive plate; and
a circuit coupled to said movable conductive plate, said circuit sensing a voltage on said movable conductive plate based on relative positions of said fixed conductive plate and said movable conductive plate, said circuit providing a phase-shifted signal describing a phase shift of said voltage with reference to said driver signal, said phase shifted signal suitable for deriving an absolute position of said movable conductive plate with respect to said fixed conductive plate.
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Specification