Adaptive vibration control using synchronous demodulation with machine tool controller motor commutation

• US 7,370,524 B2
• Filed: 08/15/2005
• Issued: 05/13/2008
• Est. Priority Date: 08/13/2004
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Inventors: Hopkins, David James
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): BELLAMY, TAMIKO D
• Application Number:
  US11/205,551
• Publication Number:
  US 20060036351A1
• Time in Patent Office: 1,002 Days
• Field of Search: 734/30, 734/57, 734/60, 734/62
• US Class Current: 73/146.2
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 13/024 in which a parameter or coefficient is automatically adjusted to optimise the performance
• CPC Class Codes: G05D 19/02 characterised by the use of electric means

Abstract

A control system and method for actively reducing vibration in a spindle housing caused by unbalance forces on a rotating spindle, by measuring the force-induced spindle-housing motion, determining control signals based on synchronous demodulation, and provide compensation for the measured displacement to cancel or otherwise reduce or attenuate the vibration. In particular, the synchronous demodulation technique is performed to recover a measured spindle housing displacement signal related only to the rotation of a machine tool spindle, and consequently rejects measured displacement not related to spindle motion or synchronous to a cycle of revolution. Furthermore, the controller actuates at least one voice-coil (VC) motor, to cancel the original force-induced motion, and adapts the magnitude of voice coil signal until this measured displacement signal is brought to a null. In order to adjust the signal to a null, it must have the correct phase relative to the spindle angle. The feedback phase signal is used to adjust a common (to both outputs) commutation offset register (offset relative to spindle encoder angle) to force the feedback phase signal output to a null. Once both of these feedback signals are null, the system is compensating properly for the spindle-induced motion.

Claims

1. A control system for dampening spindle housing vibration induced by an unbalanced rotating spindle, comprising:

an angular position sensor for sensing the rotary angular position of the spindle rotating about its spindle axis;

at least one displacement sensor(s) for measuring displacements associated with the spindle housing vibration;

means for exerting a mechanical dampening force on the spindle housing in the measurement direction(s) of the at least one displacement sensor(s); and

a controller capable of synchronously demodulating a displacement measurement with respect to a rotary angular position measurement of the spindle to determine the magnitude and location of a maximum unbalance signal, and controlling the mechanical dampening force exerting means based on said magnitude and location of the maximum unbalance signal so as to actively dampen the spindle housing vibration.

2. The system of claim 1,

wherein three displacement sensors are used to measure displacements of the spindle housing, with a first sensor positioned to measure displacement in an x-direction, and second and third sensors positioned opposite each other to measure displacement in a y-direction

and the means for exerting a mechanical dampening force on the spindle housing comprises three voice coil motors, each positioned opposite a corresponding one of the three displacement sensors.

3. The system of claim 2,

wherein the second and third sensors, and their corresponding voice coil motors, are offset from each other for sensing and controlling s rotational displacements of the spindle housing.

4. A control system for reducing spindle housing vibration induced by an unbalanced rotating spindle, comprising:

an angular position sensor for sensing the angular position of the rotating spindle;

at least one displacement sensor(s) for measuring displacements associated with the spindle housing vibration;

means for exerting a mechanical dampening force on the spindle housing in the measurement direction(s) of the at least one displacement sensor(s); and

a first controller module capable of synchronously demodulating a displacement measurement with respect to an angular position measurement of the spindle to produce a first demodulated output, and a second demodulated output which is 90 degrees out of phase from the first demodulated output;

a second controller module capable of filtering the first and second demodulated outputs to produce a magnitude of phase error correction associated with the first demodulated output, and a magnitude of amplitude error correction of the displacement measurement corresponding to the second demodulated output;

a third controller module capable of using the magnitude of amplitude error correction as input for demodulating said input with respect to the angular position measurement of the spindle;

a fourth controller module capable of recursively adjusting the angular position measurement of the spindle used by the first and third controller modules so that the magnitude of phase error correction is reduced to zero, and

a fifth controller module capable of producing a signal for actuating the means for exerting a mechanical dampening force on the spindle housing to reduce the vibrations on said spindle housing.

5. A control method for dampening spindle housing vibration induced by an unbalanced rotating spindle, comprising:

using an angular position sensor for sensing the rotary angular position of the spindle rotating about its spindle axis;

using at least one displacement sensor(s) for measuring displacements associated with the spindle housing vibration;

synchronously demodulating a displacement measurement with respect to a rotary angular position measurement of the spindle to determine the magnitude and location of a maximum unbalance signal; and

controlling a mechanical dampening force exerting means on the spindle housing based on said magnitude and location of the maximum unbalance signal so as to actively dampen the spindle housing vibration.