Accelerometers

• US 3,901,086 A
• Filed: 06/26/1974
• Issued: 08/26/1975
• Est. Priority Date: 06/30/1973
• Status: Expired due to Term

• Current Assignee: Peter Stanley Levis, William Edward Griffiths
• Original Assignee: Peter Stanley Levis, William Edward Griffiths
• Inventors: Griffiths, William Edward, Levis, Peter Stanley
• Primary Examiner(s): Gill, James J.
• Application Number:
  US05/483,416
• Time in Patent Office: 426 Days
• Field of Search: 73/490,503,516R,517B
• US Class Current: 73/490
• CPC Class Codes: G01P 15/132 with electromagnetic counterbalancing means

Abstract

An accelerometer of the force-balance type has an inertial mass, able to be displaced under the action of an acceleration force, and electromagnetic coil responsive to a current flow in the coil to generate a restoring force on the mass to oppose the acceleration force. The mass controls a switch such that when the mass is displaced under acceleration operation of the switch causes a linearly increasing current to be applied to the coil up to a predetermined value in a reference time period. The current is generated by an oscillator, a first counter and binary resistor ladder network and the time period is that for the number of oscillations required to generate the predetermined value of current. When the current flow causes the mass to be restored further operation of the switch causes a counter, started with the first counter, to stop counting. In any one reference time period the total in the second counter is an indication of the acceleration value (by equating the acceleration force with the current generated force required to overcome it). The second counter provides a serial binary output for further processing or for passing to an integrating or summating circuit to provide in the same form signals representing the velocity of, and distance travelled by, the accelerometer.

Claims

1. A force-balance accelerometer comprising an inertial mass arranged to be acted upon and displaced by an acceleration force, an electromagnetic coil responsive to a current flow therein to exert a restoring force on the mass in opposition to the acceleration force, switching means operable to maintain a first state while the acceleration force is greater than the restoring force and operable to maintain a second state while the restoring force is greater than the acceleration force, coil energising means responsive to entry of the switching means to the first state to apply to the coil a reference signal in the form of a current, the magnitude of which varies within a reference time period, and in accordance with a predetermined law, from a datum value to a predetermined reference value, thereafter returning to the datum value, and output means responsive to entry of the switching means to the second state in any reference time period to provide an output signal representative of the magnitude of the reference signal, with respect to the datum value, at which the restoring force equals the acceleration force and indicative of the magnitude of the acceleration force in that reference time period.

2. An accelerometer as claimed in claim 1 in which the coil energising means comprises an oscillator, a counter of oscillations produced, said counter being enabled to count by an external signal derived from said switching means arranged to return automatically to zero after a predetermined number of oscillations have been counted and operable to provide as an output signal the accummulating total count in binary parallel form, a resistor ladder network fed by an external voltage source and connected to the counter output such that as the count increases appropriate resistor values are switched into series with the voltage source and the coil to provide a current increasing from the datum value in a stepwise manner.

3. An accelerometer as claimed in claim 2 in which the coil energising means further comprises synchronisation means comprising a bistable element SET by the entry of the switching means to its first state to provide a counter enabling signal and RESET by return of the counter to zero to remove the signal.

4. An accelerometer as claimed in claim 2 in which the output means comprises a further counter of oscillations produced by the oscillator and responsive to entry of the switching means to its first state to begin counting and responsive to entry of the switching means to its second state to stop counting.

5. An accelerometer as claimed in claim 2 in which the output means comprises a buffer circuit having a parallel binary input, said circuit being responsive to entry of the switching means to the second state to receive the instantaneous parallel binary output of the counter of the coil energising means.

6. An accelerometer as claimed in claim 2 including a control element comprising a generator of shift pulses operable to remove the contents of the output means in response to a trigger signal.

7. An accelerometer as claimed in claim 6 in which the trigger signal is produced in response to the counter of the coil energising means returning to zero.

8. An accelerometer as claimed in claim 6 in which thE trigger signal is produced is responsive to the switching means entering the second state.

9. An accelerometer as claimed in claim 1 in which there is also provided summation means operable to summate a plurality of accelerometer output signals over a plurality of reference time periods to provide a second output signal.

10. An accelerometer as claimed in claim 9 in which the summation means comprises a serial input/output shift register and an addition element operable to add the contents of the accelerometer output means and the shift register in each reference time period and to return the contents to the shift register, the contents of the shift register comprising the said second output signal.

11. An accelerometer as claimed in claim 9 in which there is provided further summation means operable to summate the second output signal over a plurality of reference time periods to provide a third output signal indicative of the distance travelled by the accelerometer.

12. An accelerometer as claimed in claim 1 including gating means operable to inhibit the removal of output signals while those signals are changing in value.