Digital control servo system

• US 20020049513A1
• Filed: 09/21/2001
• Published: 04/25/2002
• Est. Priority Date: 09/21/2000
• Status: Active Grant

• Current Assignee: Novanta Corporation (Novanta Inc.)
• Original Assignee: GSI Lumonics Corporation (Novanta Inc.)
• Inventors: Stewart, Fredrick A., Nussbaum, Michael B., Shannon, Michael R.
• Granted Patent: US 7,200,464 B2
• Time in Patent Office: Days
• US Class Current: 700/186
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03

Abstract

An improved servo system for galvanometers, scanners and similar devices which uses digital processing to increase the dynamic range and provide greater effective resolution. The system provides digital control of a reference point that directly influences the excitation, which in turn directly influences the gain of the circuit. A high and low resolution switching path is provided to optimize dynamic range. Wide angle torque compensation improves uniformity of response at large angular deflections from zero. Improved thermal protection allows safe operation near system thermal limits. A graphical user interface allows adjustments and changes response on the fly for tuning due to input conditions or user control.

Claims

1. A digital servo system for an optical scanner, comprising a digital processor and computer code, and a signal processing circuit, said circuit comprising

a first input for an analog position command signal,

a second input for an analog position feedback signal, and

an error signal output, said circuit comprising

a first circuit element for producing from said position command signal and said position feedback signal an analog position error signal,

a second circuit element for producing from said analog position error signal a first digitized error signal known as a high resolution error signal,

a third circuit element for producing a digitized said analog position command signal,

a fourth circuit element for producing a digitized said analog position feedback signal,

said digital processor and computer code generating a second digitized error signal known as a low resolution error signal as a difference signal between said digitized command signal and said digitized feedback signal,

said digital processor and computer code providing automatic switching of said error signal output from said high resolution error signal to said low resolution signal during periods when said second circuit element is at its maximum positive or negative output limit.

2. A digital servo system for an optical scanner according to claim 1, said servo system further comprising a digitally operative scanner angle torque compensation control effort multiplier derived from digitized position feedback signal input.

3. A digital servo system for an optical scanner according to claim 1, said processor and computer code connected to a graphical user interface.

4. A digital servo system for an optical scanner according to claim 3, said graphical user interface providing simulated analog presentations of servo algorithms and operating parameters, and permitting simulated analog control inputs in real time via hand or finger motion for a multiplicity of servo system operating parameters.

5. A digital servo system for an optical scanner, comprising:

an analog position command signal input,

a digital error signal output

an analog position feedback signal processing circuit with positive and negative angular position sensors connected to an analog differential amplifier,

an analog position error signal with gain, said analog position error signal derived from said analog command and said differential amplifier by said feedback signal processing circuit,

a digital processor and computer code,

a reference voltage controlled by said processor and computer code connected to said feedback signal processing circuit for controlling gain thereof,

a high resolution error signal consisting of a digitized said analog position error signal,

a low resolution error signal consisting of a digital differential of a digitized said command signal input and a digitized said analog position error signal,

said digital processor and computer code providing automatic switching of said error signal output from said high resolution error signal to said low resolution signal during periods when said second circuit element is at its maximum positive or negative output limit.

6. A digital servo system for an optical scanner according to claim 5, further comprising a digital control output from said processor and computer code connected to said feedback signal processing circuit for adjusting the gain of said differential amplifier.

7. A digital servo system for an optical scanner according to claim 6, said gain of said differential amplifier being adjustable through two equal resistor sets in said feedback signal processing circuit, one each of said resistor sets being connected between each said position sensor and said differential amplifier, said resistor sets ganged for concurrent selection of equal subsets thereof by operation of said processor and computer code.

8. A digital servo system for an optical scanner according to claim 6, further comprising an offset voltage controlled by said processor and computer code and connected to said feedback signal processing circuit for adjusting the zero point of said servo system.

9. A digital servo system for an optical scanner according to claim 5, further comprising a digitally constructed scanner angle torque compensation control effort multiplier derived from said feedback position signal by said processor and computer code.

10. A digital servo system for an optical scanner according to claim 5, said processor and computer code connected to a graphical user interface.

11. A digital servo system for an optical scanner according to claim 10, said graphical user interface providing simulated analog presentations of servo algorithms and operating parameters, and permitting simulated analog control inputs in real time via hand or finger motion for a multiplicity of servo system operating parameters.

12. A digital servo system for an optical scanner according to claim 11, said graphical user interface comprising a general purpose computer, keyboard and a hand or finger analog motion cursor control device.

13. A digital servo system for an optical scanner according to claim 12, said processor, computer code and graphical user interface providing for simulated analog control inputs for programming of sequentially executable user constructed tunes, said tunes recordable in said processor for automated sequencing during subsequent scanner operations.

15. A digital servo system for an optical scanner according to claim 13, further comprising a thermal sensor proximate the stator, a coil current sensor, a thermal model in said processor associating temperature rise said optical scanner with coil current level, and a program in said processor for calculating said temperature rise assumed from affect of coil current and adding actual temperature from said thermal sensor.

14. A process for calculating system operating temperature in a galvanometer, comprising the steps of:

sensing stator temperature of a galvanometer with a thermal sensor proximate the stator,

sensing coil current in said galvanometer,

calculating temperature rise from stator to coil from effect of coil current, and

adding calculated temperature rise to ambient stator temperature.