United States Patent 3,643,513 (HW 2-25) (RCTA)

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General Information

Assignment: Figure out how the best embodiment works and also what is claimed. Pretend your boss gave them to you and wants to know how they work and what is claimed so that your company's product can be evaluated in terms of patentability.

  • Accelerometer
  • Inventor: Preston R. Weaver
  • Assignee: UMC Electronics Company
  • Filed: Aug. 1, 1968
  • Issued: Feb. 22, 1972

Workings and Claims

N.B. Numbers refer to diagram numbers in the Weaver patent.

The Weaver patent describes an accelerometer that senses and records acceleration loading of an aircraft that is due only to structurally damaging airplane maneuvers of pronounced durations. It uses an electrical signal that is proportional to the loading and magnitude of loading above a threshold value to accomplish this task (i.e. it generates a voltage waveform). The device is able to discriminate between loads due to maneuvers and parasitic accelerations resulting from local vibrations or high-frequency impulses.

A prior Weaver patent describes an accelerometer that functions using a mechanical switch—as opposed to the electrical switch disclosed here. It required switches of large dimensions and employed damping techniques that were difficult to control due to temperature sensitivity and lack of sharp rolloff. The current Weaver patent circumvents these problems by employing electric and electromagnetic sensors.

The Weaver accelerometer employs flexure members arranged such that they achieve linear motion within a high degree of sensitivity along their axis. They do not respond to accelerations that are transverse to this axis. Further, in order to generate an electrical signal that is proportional to the loads experienced by the aircraft, the accelerometer uses the displacement of a seismic mass. The force coil (17) and capacitative displacement sensor (18) comprise this seismic mass. While the mass remains stationary, plate 19 moves with the permanent magnet assembly (11) and the accelerometer case (10). This displacement between the seismic mass and the case allows sensor 18 to create an output signal. This motivates a current through the force coil (17). The current through the force coil (17) results in an electromagnetic field. This field interacts with the permanent magnetic field and creates a force that returns the seismic mass to its starting position.

As shown in Figure 3, a voltage E is generated that is proportional to acceleration loading. Weaver discloses the control scheme necessary to generate this output signal. When the seismic mass is displaced, the capacitance bridge (26) becomes displaced, applying a high-frequency signal across the diode bridge (28). The diode bridge (28) then creates an output voltage that is proportional to the unbalance of the capacitance bridge (26). The voltage is fed to a differential amplifier (29). A series of signals goes through a current amplifier (30) and back to the force coil (17) (whose current results in the restorative force). The current through the force coil (17) flows to terminal 31, which is connected to an RLC filter. The filter uses a reference level that is a fraction of the supply voltage as determined by the ratio of resistances 42 and 43. The response of two filters working together allows for a well-defined corner frequency and high rolloff. There is much greater sensitivity than in the mechanical accelerometer. The filters also serve to discriminate the loading signals from the higher frequency signals.

The accelerometer can also sense and record duration of load. If the duration does not meet a threshold value, it can be eliminated from the record. The voltages referenced in the patent are used on for illustrative purposes and may be altered as necessary.

When the acceleration signal E reaches a value of 1.5 volts at time t0, timer 53 is energized. Timer 53 begins a timing cycle. At time t1, timer 53 applies a signal to information release gate 54. Gate 54 energizes line 55 to all the counting devices. Before gate 54 energizes the other devices, amplifiers 46b and 47b turn on and latches 46c and 47c latch. Their contacts (56) in the associated counter circuits then close. As the voltage signal E increases, other amplifiers turn on and their latches close their contacts to latch in. In turn, other coils become energized. At time t2, or if the signal falls below the reference level, the associated amplifier will turn off and the switches will release. The relays are deenergized and their contacts open. Thus, the acceleration forces are only recorded if they persist for a predetermined time.

Weaver claims an accelerometer for counting a variety of acceleration maneuvering loadings of predetermined magnitude. He claims the means for providing a signal proportional to these accelerations, of sensing and storing those signals, of recording the accelerations levels, of timing their cycles, and of determining the response relative to a reference level. He further claims the means for filtering high-frequency components from the wave signal employed in this device. He claims the means and arrangement of gates that apply an advance signal from the sensing and storing means to the counters. Finally, he claims the means for sensing when a signal exceeds a reference value and for disabling the sensing and storing means if the signal falls below the reference value.