Angular position sensing and control system, apparatus and method

• US 3,974,699 A
• Filed: 03/10/1975
• Issued: 08/17/1976
• Est. Priority Date: 08/28/1973
• Status: Expired due to Term

• Current Assignee: New SD, Inc.
• Original Assignee: Systron Donner Corporation (Parker-Hannifin Corporation)
• Inventors: Sigworth, Frederick J., Morris, Harold D.
• Primary Examiner(s): Gill, James J.
• Application Number:
  US05/556,572
• Time in Patent Office: 526 Days
• Field of Search: 73/178, 73/504, 73/510, 73/432 R, 235/150.25, 33/328
• US Class Current: 73/865.9
• CPC Class Codes: E02F 3/764 with the scraper blade being pivotable about a vertical axis
• CPC Class Codes: E02F 3/765 with the scraper blade being pivotable about a horizontal axis disposed perpendicular to the blade
• CPC Class Codes: E02F 3/845 using mechanical sensors to determine the blade position, e.g. inclinometers, gyroscopes, pendulums
• CPC Class Codes: G05D 3/14 using an analogue comparing device

Abstract

A structural body is monitored in angular position about at least one axis by utilizing a level sensor and a sensor responsive to angular motion of the body about the axis being monitored. An output indicative of long term angular variations of the body about the axis is provided by the level sensor and short term angular variations are indicated by the output from the sensor responsive to angular motion about the axis. The signals indicative of long term and short term angular variations are combined to provide a broad band output signal indicative of angular position which is immune to high frequency translational variations appearing at the level sensor output, but which is responsive to high frequency angular inputs. The fast response angular sensor output is compared with the slow response level sensor output and an error signal is produced which drives the angular sensor output signal into coincidence with the level sensor output signal. The combined broad band angular output indication may be utilized for angular position monitoring for controlling one part of a machine relative to a predetermined external angular position reference for driving a stable platform to assume a predetermined angle about the axis.

Claims

1. In apparatus for sensing the attitude relative to a local horizontal reference of a part on a machine having a framework supporting said part while said framework is free to move relative to the local horizontal reference, a linear accelerometer adapted to be mounted on said part having a sensitive axis for detecting departure thereof from the local horizontal reference and for producing a first signal representing a slow response angular displacement of said part, means for summing connected to receive said first signal and producing a summed output, means for receiving said summed output and for attenuating high frequencies therein, said last named means providing an error compensation signal, means adapted to be mounted on said part for sensing rotational motion thereof, said last named means producing a second signal representing a fast response indication of angular displacement of said part, means for combining said error compensation signal and said second signal and for providing a combined signal, means for feeding back said combined signal to said means for summing, said first signal and said combined signal having opposing sense for the same motion sense, whereby steady state errors in said second signal are compensated in said combined signal by said error compensation signal and transients in said second signal appear in said combined signal.

2. Apparatus as in claim 1 wherein said means for sensing rotational motion comprises an angular accelerometer, said second signal being an output indicative of angular acceleration, and said means for combining including means for double integrating said output indicative of angular acceleration.

3. Apparatus as in claim 1 wherein said means for sensing rotational motion comprises an angular rate gyro, said second signal being an output indicative of angular velocity, and said means for combining including means for performing a single integration of said output indicative of angular velocity.

4. In a sensing apparatus a linear accelerometer for producing a first signal, an angular accelerometer for producing a second signal, means for receiving said first signal, said means for receiving operating to pass steady state signals, to attenuate transient signals, and to provide a compensation signal, means for combining said compensation signal and said second signal and for providing a combined output signal, said combined output signal containing components resulting from said second signal having a sense opposite to said first signal for the same motion sense, means for coupling said combined output signal to said means for receiving, said combined output signal thereby being substantially free of the effects of spurious linear acceleration in said first signal and being substantially free of steady state errors in said second signal.

5. In an angular position sensing system for broad band detection of the angular position of a structural body referenced to earth'"'"'s coordinates about at least one axis, a level sensor mounted to detect angular position of the structural body about said one axis and producing an angular position output related thereto, means for attenuating short term components in said angular position output and providing a long term angular position output, means for detecting angular motion about said one axis substantially solely sensitive to angular motion and producing an angular motion output related thereto, means for combining said long term angular position and motion outputs, said means for combining including means for converting said angular motion output to a second angular position output, whereby a combined angular position output is produced, said combined angular position output being coupled to said means for attenuating, whereby short term second angular position output is present in said combined angular position output thereby providing a continuous broad band combined angular position output containing long and short term outputs related to angular position.

6. An angular position sensing system as in claim 5 together with means for providing a reference signal for said one axis indicative of a predetermined angular position of the structural body about said one axis, and means for comparing the combined angular position output with said reference signal for generating an error signal, said error signal providing indication of angular departure from said predetermined angular position.

7. An angular position sensing system as in claim 5 wherein said level sensor comprises a linear accelerometer having a sensitive axis oriented perpendicular to said one axis of rotation, wherein said means for detecting angular motion includes an angular accelerometer having a sensitive axis oriented parallel to said one axis of rotation, wherein said means for converting includes a double integrator for receiving said angular motion output and providing said second angular position output.

8. An angular position sensing system as in claim 5 wherein said level sensor comprises a linear accelerometer having a sensitive axis oriented perpendicular to said one axis of rotation, said angular position output providing a steady state output signal responsive to rotational movement of said sensitive axis about said one axis, and said means for detecting angular motion comprises an angular velocity transducer having a sensitive axis oriented parallel to said one axis of rotation, said angular motion output providing a transient output signal responsive to rotational movement, wherein said means for converting includes an integrator for receiving said transient output signal and for providing said second angular position output, and wherein said long term angular position outputs are below a corner frequency and said short term second angular position outputs are above said corner frequency.

9. An angular position sensing system as in claim 5 wherein said level sensor and means for detecting angular motion are mounted directly to the structural body, together with means for measuring linear displacement having a sensitive axis aligned with the nominal vertical axis of the structural body, and producing output related to displacement along the nominal vertical axis, and coordinate transformation means for receiving said combined angular position output and said output related to displacement and for transforming structural body displacement to earth'"'"'s coordinate displacement, whereby an output signal indicative of vertical displacement of the structural body is provided.

10. The method of sensing the angular position of a structural body relative to a predetermined angular position about at least one axis referenced to earth'"'"'s coordinates, comprising the steps of sensing the deviation from local horizontal of a plane in the body about said one axis, sensing the angular acceleration of the body about said one axis, rejecting the high frequency components in the sensed deviation from local horizontal, integrating the sensed angular acceleration twice, rejecting the low frequency components in the twice integrated signal, and combining the remaining low and high frequency components in the sensed deviation and twice integrated signals respectively, thereby providing a broad band signal indicative of angular position.

11. Apparatus for sensing angular position of a structure about an axis wherein the structure is free to move about the axis comprising a level sensor for monitoring angular position of the structure relative to a level reference and providing a level indicative output, an angular motion sensor for monitoring angular motion of the structure about the axis and providing an angular motion indicative output, a compound amplifier, first and second means for summing included in said compound amplifier, said level indicative output being coupled to said first means for summing, and said angular motion indicative output being coupled to said second means for summing, said compound amplifier operating to convert said angular motion indicative output to an angular position indicative output and to provide a combined angular position indicative output including components related to said angular position and level indicative outputs, means for feeding back said combined angular position indicative output to said first means for summing, said compound amplifier further operating to remove long term angular position indicative outputs and short term level indicative outputs from said combined angular position indicative output, thereby providing said last named output free of errors induced by steady state angular motion indicative output and transient level indication output.

12. Apparatus as in claim 11 wherein said compound amplifier comprises a positive follower having said first means for summing connected to the input thereof, said positive follower operating to amplify low frequency inputs, to attenuate high frequency inputs, and to provide an error compensation signal, said error compensation signal being coupled to said second means for summing, and an inverting amplifier having said second means for summing connected to the input thereof and providing said combined angular position indicative output.

13. Apparatus as in claim 11 wherein said compound amplifier includes means for providing said components related to angular position and level indicative outputs with a sense opposing the sense of said angular motion and level indicative outputs for the same sense of angular displacement.