Current control loop bias calibration by integration
View Patent ↗Ascertaining through integration a bias calibration level for a current control loop of a driver motor of a tape drive. The driver motor includes a current controller having as inputs a demand signal, a bias signal, and a feedback signal. The current controller includes an integrator coupled to the output. The method includes setting the demand signal to a zero current level, setting the bias signal to a level that substantially prevents the integrator from driving itself high, stepping down the bias signal to form a stepped down bias signal, measuring a sense parameter at the output of the current controller, determining whether the sense parameter is high for the stepped down bias signal, and setting the bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator is not driven high when the demand signal is set to the zero current level.
1. A method for ascertaining through integration a bias calibration level for a current control loop of a driver motor, the driver motor includes a current controller having as inputs a demand signal, a bias signal, and a feedback signal, the current controller includes an integrator having an output that is coupled to the output of the current controller, the method comprises:
setting the demand signal to a zero current level;
setting the bias signal to a level that substantially prevents the integrator from driving the output toward the positive voltage direction;
stepping down the bias signal by an amount quantified by a step size to form a stepped down bias signal;
measuring a sense parameter at the output of the current controller;
determining whether the sense parameter is high for the stepped down bias signal; and
when the determination is made that the sense parameter is high, setting the bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator is not driving the output toward the positive voltage direction when the demand signal is set to the zero current level.
2. The method as defined in claim 1 , further comprising when the determination is made that the sense parameter is not high, repeating the steps of stepping down, measuring, and determining until a high determination is reached.
3. The method as defined in claim 1 , further comprising disabling the feedback signal prior to the step of stepping down the bias signal.
4. The method as defined in claim 3 , wherein the step of disabling comprises isolating the current controller.
5. An apparatus for ascertaining through integration a bias calibration level for a current control loop of a driver motor, the driver motor includes a current controller having as inputs a demand signal, a bias signal, and a feedback signal, the current controller includes an integrator having an output that is coupled to the output of the current controller, the apparatus comprises:
means for setting the demand signal to a zero current level;
means for setting the bias signal to a level that substantially prevents the integrator from driving the output toward the positive voltage direction;
means for stepping down the bias signal by an amount quantified by a step size to form a stepped down bias signal;
means for measuring a sense parameter at the output of the current controller;
means for determining whether the sense parameter is high for the stepped down bias signal; and
when the determination is made that the sense parameter is high, means for setting the bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator is not driving the output toward the positive voltage direction when the demand signal is set to the zero current level.
6. The apparatus as defined in claim 5 , further comprising means for disabling the feedback signal.
7. The apparatus as defined in claim 6 , wherein the means for disabling comprises means for isolating the current controller.
8. A method for ascertaining through integration at least one bias calibration level for a tape drive, the tape drive includes a motor controller, a first current controller, and a second motor controller, the motor controller includes a sense input, a first demand output, a first bias output, a second demand output, and a second bias output, the first current controller includes a demand input coupled to the first demand output, a bias input coupled to the first bias output, a feedback input, an output coupled to the sense input, and an integrator having an output coupled to the output of the first current controller, the second current controller includes a demand input coupled to the second demand output, a bias input coupled to the second bias output, a feedback input, an output coupled to the sense input, and an integrator having an output coupled to the output of the second current controller, the method comprises:
isolating the second current controller from the sense input;
setting the first demand output to a zero current level;
setting the first bias output to a level that substantially prevents the integrator of the first current controller from driving the output toward the positive voltage direction;
stepping down the first bias output by an amount quantified by a step size to form a stepped down bias output;
measuring a sense parameter at the sense input;
determining whether the sense parameter is high for the stepped down bias output; and
when the determination is made that the sense parameter is high, setting a first bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator of the first current controller is not driving the output toward the positive voltage direction when the first demand output is set to the zero current level.
9. The method as defined in claim 8 , further comprising when the determination is made that the sense parameter is not high, repeating the steps of stepping down, measuring, and determining until a high determination is reached.
10. The method as defined in claim 8 , further comprising disabling the feedback input of the first current controller prior to the step of stepping down the bias output.
11. The method as defined in claim 8 , further comprising:
isolating the first current controller from the sense input;
setting the second demand output to a zero current level;
setting the second bias output to a level that substantially prevents the integrator of the second current controller from driving the output toward the positive voltage direction;
stepping down the second bias output by an amount quantified by a step size to form a stepped down bias output;
measuring a sense parameter at the sense input;
determining whether the sense parameter is high for the stepped down bias output; and
when the determination is made that the sense parameter is high, setting a second bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator of the second current controller is not driving the output toward the positive voltage direction when the second demand output is set to the zero current level.
12. The method as defined in claim 11 , further comprising when the determination is made that the sense parameter is not high, repeating the steps of stepping down, measuring, and determining until a high determination is reached.
13. The method as defined in claim 11 , further comprising disabling the feedback input of the second current controller prior to the step of stepping down the bias output.
14. An apparatus for ascertaining through integration at least one bias calibration level for a tape drive, the tape drive includes a motor controller, a first current controller, and a second motor controller, the motor controller includes a sense input, a first demand output, a first bias output, a second demand output, and a second bias output, the first current controller includes a demand input coupled to the first demand output, a bias input coupled to the first bias output, a feedback input, an output coupled to the sense input, and an integrator having an output coupled to the output of the first current controller, the second current controller includes a demand input coupled to the second demand output, a bias input coupled to the second bias output, a feedback input, an output coupled to the sense input, and an integrator having an output coupled to the output of the second current controller, the apparatus comprises:
means for isolating the second current controller from the sense input;
means for setting the first demand output to a zero current level;
means for setting the first bias output to a level that substantially prevents the integrator of the first current controller from driving the output toward the positive voltage direction;
means for stepping down the first bias output by an amount quantified by a step size to form a stepped down bias output;
means for measuring a sense parameter at the sense input;
means for determining whether the sense parameter is high for the stepped down bias output; and
when the determination is made that the sense parameter is high, means for setting a first bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator of the first current controller is not driving the output toward the positive voltage direction when the first demand output is set to the zero current level.
15. The apparatus as defined in claim 14 , further comprising means for disabling the feedback input of the first current controller.
16. The apparatus as defined in claim 14 , further comprising:
means for isolating the first current controller from the sense input;
means for setting the second demand output to a zero current level;
means for setting the second bias output to a level that substantially prevents the integrator of the second current controller from driving the output toward the positive voltage direction;
means for stepping down the second bias output by an amount quantified by a step size to form a stepped down bias output;
means for measuring a sense parameter at the sense input;
means for determining whether the sense parameter is high for the stepped down bias output; and
when the determination is made that the sense parameter is high, means for setting a second bias calibration level to a level sufficiently above the stepped down bias signal such that the integrator of the second current controller is not driving the output toward the positive voltage direction when the second demand output is set to the zero current level.
17. The apparatus as defined in claim 16 , further comprising means for disabling the feedback input of the second current controller prior to the step of stepping down the bias output.
18. A tape drive enabled to ascertain through integration at least one bias calibration level for a current control loop of the tape drive, the tape drive comprises:
a motor controller including a sense input, a first demand output, and a first bias output; and
a first current controller including a demand input coupled to the first demand output, a bias input coupled to the first bias output, an output coupled to the sense input, and an integrator having an output coupled to the output of the first current controller,
wherein the sense input is utilized during a calibration sequence to ascertain a first bias calibration level for the first current controller where the integrator of the first current controller is not driving the output toward the positive voltage direction when the first demand output is set to a zero current level and the first bias output is set to the first bias calibration level.
19. The tape drive as defined in claim 18 , wherein the motor controller further includes a second demand output and a second bias output and the tape drive further comprises:
a second current controller including a demand input coupled to the second demand output, a bias input coupled to the second bias output, an output coupled to the sense input, and an integrator having an output coupled to the output of the second current controller,
wherein the sense input is utilized during a calibration sequence to ascertain a second bias calibration level for the second current controller where the integrator of the second current controller is not driving the output toward the positive voltage direction when the second demand output is set to a zero current level and the second bias output is set to the second bias calibration level.
20. The tape drive as defined in claim 18 , further comprising a signal processor connected in series with the sense input of the motor controller.