Control methods for the reduction of limit cycle oscillations for haptic devices with displacement quantization
First Claim
1. In a haptic device having a manipulandum, wherein a position of the manipulandum is determined at regular sampling times, a method for reducing limit cycle oscillations of the manipulandum, comprising:
- in a first servo loop operating at a first servo rate, determining a primary force based on the position of the manipulandum at a current sampling time;
in a second servo loop operating at a second servo rate;
detecting an oscillation of the manipulandum; and
determining a secondary force in response to the oscillation;
combining the primary force and the secondary force; and
applying the combined force to the manipulandum.
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Abstract
Systems and methods for reducing limit cycle oscillations of a haptic device. A net force applied to the device is a combination of a primary force computed in a main haptic loop and a secondary force computed in a damping loop that cancels or minimizes the oscillations. Various algorithms for computing the secondary force are provided. In one algorithm, the secondary force is determined from the momentum error associated with crossing of a wall position by the manipulandum and is applied immediately after the crossing is detected. In another algorithm, a periodically varying secondary force with a phase shift relative to the phase of the oscillating manipulandum is computed.
100 Citations
30 Claims
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1. In a haptic device having a manipulandum, wherein a position of the manipulandum is determined at regular sampling times, a method for reducing limit cycle oscillations of the manipulandum, comprising:
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in a first servo loop operating at a first servo rate, determining a primary force based on the position of the manipulandum at a current sampling time;
in a second servo loop operating at a second servo rate;
detecting an oscillation of the manipulandum; and
determining a secondary force in response to the oscillation;
combining the primary force and the secondary force; and
applying the combined force to the manipulandum. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
computing a momentum error associated with the crossing of the virtual wall position; and
computing a secondary force offsetting the momentum error.
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5. The method of claim 4, wherein computing a momentum error associated with the crossing includes:
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computing an applicable force for a position inside the virtual wall region;
computing an error time corresponding to a time spent inside the virtual wall region before the applicable force is applied; and
multiplying the applicable force by the error time.
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6. The method of claim 5, wherein computing an applicable force for a position inside the virtual wall region includes:
computing the product of a spring constant associated with the virtual wall times a displacement resolution associated with the position of the manipulandum.
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7. The method of claim 5, wherein computing an error time includes:
setting the error time equal to half an interval between sampling times.
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8. The method of claim 4, wherein computing a secondary force offsetting the momentum error includes:
dividing the momentum error by a period of the second servo loop.
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9. The method of claim 1, wherein detecting an oscillation includes detecting at least two crossings of a zero position by the manipulandum within a predetermined time interval.
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10. The method of claim 9, wherein determining a secondary force in response to the oscillation includes:
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computing a period of the oscillation;
identifying a last zero crossing time;
computing a displacement phase of a periodic displacement function based on the oscillation period and the last zero crossing time;
computing a secondary force from the displacement phase, the secondary force having a damping phase offset from the displacement phase by a constant offset.
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11. The method of claim 10, wherein computing an oscillation period includes:
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identifying two successive zero crossing times; and
computing an oscillation period equal to twice the difference between the two successive zero crossing times.
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12. The method of claim 9, wherein the zero position corresponds to a position of a virtual wall.
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13. A control system for a haptic device having a manipulandum, comprising:
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a processor configured to generate a primary force signal at a main haptic loop rate;
a damping circuit configured to detect an oscillation of the manipulandum and to generate a secondary force signal at a damping loop rate in response to the detected oscillation; and
a combining circuit configured to combine the primary force signal and the secondary force signal, thereby generating a control signal for controlling a haptic feedback force of the haptic device. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A haptic feedback device, comprising:
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a manipulandum;
an actuator coupled to the manipulandum and configured to exert a force on the manipulandum in response to an actuator control signal;
a processor configured to generate a primary force signal at a main haptic loop rate;
a damping circuit configured to detect an oscillation of the manipulandum and to generate a secondary force signal in response to the detected oscillation; and
a combining circuit configured to combine the primary force signal and the secondary force signal, thereby generating the actuator control signal. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30)
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Specification