Spectrometer with direct drive high speed oscillating grating

• US 4,969,739 A
• Filed: 01/09/1989
• Issued: 11/13/1990
• Est. Priority Date: 01/09/1989
• Status: Expired due to Term

• Current Assignee: NIR Instruments Company
• Original Assignee: Nirsystems Incorporated
• Inventors: McGee, Philip A.
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US07/294,679
• Time in Patent Office: 673 Days
• Field of Search: 356/305, 356/308, 356/328, 356/334
• US Class Current: 356/308
• CPC Class Codes: G01J 2003/062 motor-driven
• CPC Class Codes: G01J 2003/1213 Filters in general, e.g. dichroic, band
• CPC Class Codes: G01J 2003/1273 Order selection
• CPC Class Codes: G01J 3/06 Scanning arrangements arrangements for order-selection
• CPC Class Codes: G01J 3/18 using diffraction elements, e.g. grating gratings per se G02B
• CPC Class Codes: H02P 7/04 by means of a H-bridge circuit

Abstract

An optical grating is oscillated at a high rate to scan a narrow wavelength band of light through the spectrum dispersed by the grating. The grating is connected integrally with the rotor of a motor, which is energized to oscillate its rotor between selected limits. The direction of rotation of the motor is controlled by an H drive circuit connected to a coil of the motor. The speed of the motor is controlled by a pulse train applied to the motor coil through the H drive. The pulse train has a duty cycle varying inversely with the motor speed. The duty cycle of the pulse train is controlled by a counter which is connected to count high frequency pulses and which is reset each time the grating rotates through an angular increment. The limits of the oscillation of the grating and the rate of rotation of the grating between the limits are selectively variable. Output readings from the spectrophotometer are taken at equal angular increments of the grating and these readings are converted to values occurring at equal wavelength increments by a computer.

Claims

1. An optical instrument comprising an optical grating mounted for oscillating, means to illuminate said grating with light radiation to cause said radiation to disperse said radiation into a spectrum, means to receive a narrow bandwidth of the spectrum dispersed by said grating, a motor having its rotor fixed to said grating so that said rotor and said grating rotate as one piece, and motor control means to energize said motor to oscillate said rotor between limits to thereby oscillate said grating and scan the narrow wavelength band to be received by said receiving means through said spectrum, said motor control means energizing said motor with a first polarity of electrical energy to positively drive said motor in one direction between said limits in the oscillation of said motor and energizing said motor with a second polarity of electrical energization to positively drive said rotor in the opposite direction between said limits in said oscillation.

2. An optical instrument comprising an optical grating mounted for oscillating, means to illuminate said grating with light radiation to cause said radiation to disperse said radiation into a spectrum, means to receive a narrow bandwidth of the spectrum dispersed by said grating, a motor having its rotor fixed to said grating so that said rotor and said grating rotate as one piece, and motor control means to energize said motor to oscillate said rotor to thereby oscillate said grating and scan the narrow wavelength band to be received by said receiving means through said spectrum, said motor control means including means to indicate the angular position of said grating and means to reverse the direction of rotation of said motor in response to said position indicating means indicating an angular position at one of two preselected limits of the oscillation of said grating.

3. An optical instrument comprising an optical grating mounted for oscillating, means to illuminate said grating with light radiation to cause said radiation to disperse said radiation into a spectrum, means to receive a narrow bandwidth of the spectrum dispersed by said grating, a motor having its rotor fixed to said grating so that said rotor and said grating rotate as one piece, and motor control means to energize said motor to oscillate said rotor to thereby oscillate said grating and scan the narrow wavelength band to be received by said receiving means through said spectrum, said motor control means including speed control means to accelerate the motor speed quickly to a target speed each time the direction of rotation of said motor reverses at one of the limits of the motor oscillation and the maintain the speed of rotation of said motor at said target speed until the angular position of said grating reaches the other one of the limits of the motor oscillation.

4. An optical instrument as recited in claim 3 wherein said motor includes a coil arranged to torque said rotor in accordance with the energization of said coil and wherein said motor speed control means includes means to energize said coil with a pulse train having a duty cycle varying inversely with the speed of said motor.

5. An optical instrument as recited in claim 3 wherein said speed control means includes a counter connected to count high frequency clock pulses, means to reset said counter each time said grating rotates through an angular increment and means to control the speed of said motor between said limits in accordance with the count in said counter each time said counter is reset.

6. In an optical instrument having an optical grating mounted for oscillation, a motor coupled to said grating to oscillate the grating between limits, said motor having a coil arranged to torque said motor in accordance with the energization of said coil, the improvement comprising means to energize said coil with a pulse train having a duty cycle varying inversely with the speed of said motor between said limits.

7. In an optical instrument as recited in claim 6, wherein the duty cycle of said pulse train varies from a hundred percent at the limits of said oscillation to a minimum duty cycle just great enough to maintain the angular rate of rotation of said grating at a selected target speed.

8. An optical instrument as recited in claim 7, wherein said selected target speed is selectively variable.

9. An optical instrument as recited in claim 6, wherein said means to energize said motor includes a counter connected to count high frequency clock pulses, means to reset said counter each time said grating rotates through a predetermined angular increment, and mean to control said duty cycle in accordance with the count in said counter each time said counter is reset.

10. In an optical instrument having an optical grating mounted for oscillation, a motor coupled to said grating and means to energize said motor to oscillate said grating between limits, the improvement wherein said means to energize said motor includes motor speed control means to accelerate said motor quickly to a target value each time said motor reverses direction at one of said limits, said motor speed control means including a counter connected to count high frequency clock pulses, means to reset said counter each time said grating rotates through an angular increment, and means to control the speed of said motor between said limits in accordance with the count in said counter each time said counter is reset.

11. An optical instrument comprising an optical grating mounted for oscillation, means to illuminate said grating with light radiation to cause said grating to disperse said radiation into a spectrum, means to receive a narrow bandwidth of the spectrum dispersed by said grating, a motor having its rotor fixed to said grating so that said rotor and said grating rotate as one piece, a motor control means to oscillate said motor between limits to thereby oscillate said grating and scan the narrow wavelength band to be received by said receiving means through said spectrum, said motor control means energizing said motor by applying a sequence of pulses to said motor as said motor is driven in one direction between said limits to control the speed of said motor as it is driven between said limits.