Linearized force measuring apparatus

Claim 2

Linearized force measuring apparatus, comprising, in combination, a differential capacitor having a first plate, a second plate mounted parallel to said first plate in a reference position at a predetermined distance from said first plate and adapted to move in the direction perpendicular to said first plate under action of the force being measured, a third plate mounted in a fixed position parallel to said second plate at said predetermined distance therefrom on the side away from said first plate; displacement measuring means connected to said capacitor for furnishing a displacement signal having an amplitude varying as a function of displacement of said second plate from said reference position; analog/pulse converter means connected to said displacement measuring means and having a first and second converter output, for furnishing a sequence of positive pulses and a sequence of negative pulses at said first and second converter outputs respectively, the difference between the number of said positive and the number of said negative pulses per unit time varying as a function of said amplitude of said displacement signal, the total number of pulses per unit time remaining constant; and connecting means for connecting said converter output to said capacitor in such a manner that the electric force on said second plate created by said pulses opposes said force being measured, whereby the difference between the number of said positive and the number of said negative pulses per unit time constitutes a measure of the amplitude of said force being measured.

Claim 3

Force measuring apparatus as set forth in claim 1, wherein said analog/pulse converter means comprises comparator means connected to said displacement measurement means, for comparing said displacement signal to a reference signal and furnishing a positive and negative comparator output signal when said displacement signal is, respectively, greater than or less than said reference signal; timing signal furnishing means for furnishing timing signals at predetermined time intervals; and pulse furnishing means connected to said timing signal furnishing means and said comparator means, for furnishing a positive pulse at said first converter output in response to the simultaneous presence of a timing signal and said positive comparator output signal and for furnishing a negative pulse at said second converter output in response to the simultaneous presence of a timing signal and said negative comparator output signal, whereby the number of pulses per unit time corresponds to the number of said timing signals per unit time while the polarity of said pulses corresponds to the polarity of said comparator output signal.

Claim 4

Apparatus as set forth in claim 2, wherein said pulse furnishing means comprise control bistable circuit means adapted to change from a first to a second stable state in response to the simultaneous presence of said negative comparator output signal and one of said timing signals and from said second to said first stable state in response to the simultaneous presence of one of said timing signals and said positive comparator output signal, fur furnishing a first and second polarity control signal when in said first and second state respectively; and first and second bistable circuit means connected to said control bistable circuit means for furnishing said positive and negative pulses under conTrol of said timing signals in response to said first and second polarity control signals respectively.

Claim 5

Apparatus as set forth in claim 3, wherein said second bistable circuit means comprise a first constant voltage source for furnishing a positive d.c. voltage, a first bistable multivibrator having a set state for connecting said positive d.c. voltage to said first converter output, a reset state for connecting ground potential to said first converter output, and adapted to change from said reset to said set state under control of said timing signal only in the presence of said first polarity control signal; and wherein said second bistable circuit means comprise a second constant voltage source for furnishing a negative d.c. voltage, a second bistable multivibrator interconnected between said second constant voltage source and said second converter output, for applying said negative d.c. voltage to said second converter output when in a set state and for applying zero potential to said second converter output when in the reset state, said second multivibrator switching from said reset to said set state under control of said timing signal only in the presence of said second polarity control signal.

Claim 6

Apparatus as set forth in claim 2, wherein said force to be measured acts in a first direction or in a second direction opposite to said first direction; wherein said comparator means comprise a first comparator and a second comparator for comparing said displacement signal to a determined positive and negative voltage respectively, and furnishing said first and second polarity control signal only when said displacement signal is more positive than said determined positive voltage and more negative than said determined negative voltage, respectively; and wherein said pulse furnishing means comprise a first and second flip-flop each having a set and reset input, a set and reset output, and a clock input connected to receive said timing signals, means for connecting the respective set outputs to the corresponding reset inputs and the respective reset outputs to the corresponding set inputs, and means for connecting said set input of said first flip-flop to the output of said first comparator and said set input of said second flip-flop to the output of said second comparator, a first constant voltage source furnishing a positive d.c. voltage, a second constant voltage source furnishing a negative d.c. voltage, a first bistable multivibrator adapted to trigger on positive-going pulse edges, having a set input connected to said set output of said first flip-flop and a reset input connected to said reset output of said first flip-flop, and interconnected between said first constant voltage source and said first converter output in such a manner that said positive voltage is applied to said first converter output when said first bistable multivibrator is set, second bistable circuit means, adapted to trigger on negative-going pulse edges, having a set input connected to said reset output of said second flip-flop and a reset input connected to said set output of said first flip-flop, and inter-connected between said second constant voltage source and said second converter output in such a manner that said negative voltage is applied to said second converter output when said second bistable multivibrator is set.

Claim 7

Force measuring apparatus comprising, in combination, a capacitor having a first plate and a second plate mounted parallel to said first plate in a reference position at a predetermined distance from said first plate and adapted to move in the direction perpendicular to said first plate under action of the force being measured; displacement measuring means connected to said capacitor for furnishing a displacement signal having an amplitude varying as a function of displacement of said second plate from said reference position; analog/pulses converter means connected to said displacement measuring means and having a converter output, for furnishing a sequence of pUlses at said converter output, the number of pulses per unit time in said sequence of pulses varying as a function of said amplitude of said displacement signal, while the amplitude and width of said pulses remain substantially constant; and connecting means for connecting said converter output to said capacitor in such a manner that the electric force on said second plate created by said pulses opposes said force being measured, whereby the number of pulses per unit time in said sequence of pulses at said converter output constitutes a measure of the amplitude of said force being measured.

Claim 8

Force measuring apparatus comprising, in combination, a capacitor having a first plate and a second plate mounted parallel to said first plate in a reference position at a predetermined distance from said first plate and adapted to move in the direction perpendicular to said first plate under action of the force being measured; displacement measuring means connected to said capacitor for furnishing a displacement signal having an amplitude varying as a function of displacement of said second plate from said reference position; analog/pulses converter means connected to said displacement measuring means and having a converter output, for furnishing a sequence of pUlses at said converter output, the number of pulses per unit time in said sequence of pulses varying as a function of said amplitude of said displacement signal, while the amplitude and width of said pulses remain substantially constant; and connecting means for connecting said converter output to said capacitor in such a manner that the electric force on said second plate created by said pulses opposes said force being measured, whereby the number of pulses per unit time in said sequence of pulses at said converter output constitutes a measure of the amplitude of said force being measured.

Claim 9

Apparatus as set forth in claim 6, further comprising amplifier means having a predetermined amplification factor connected to the output of said displacement measuring means; and switch means connected between the output of said amplifier means and said capacitor for connecting said output of said amplifier means to said capacitor in synchronism with the application of said pulses to said capacitor.

Claim 10

Apparatus as set forth in claim 5, further comprising auxiliary amplifier means having a predetermined amplification factor and having an input connected to the output of said displacement measurement means; wherein said third plate of said capacitor comprises a first and second planar conducting surface respectively opposite said first and second plates, and insulator means between said first and second conducting planar surfaces; further comprising first and second switch means for connecting the output of said auxiliary amplifier means to said first and second conducting planar surfaces respectively under control of said timing pulses, in such a manner that said first switch means operates in synchronism with the pulses in said sequence of positive pulses and said second switch means operates in synchronism with the pulses in said sequence of negative pulses. 28

Claim 11

Force measuring apparatus comprising, in combination, a capacitor having a first plate and a second plate mounted parallel to said first plate in a reference position at a predetermined distance from said first plate and adapted to move in the direction perpendicular to said first plate under action of the force being measured; displacement measuring means connected to said capacitor for furnishing a displacement signal having an amplitude varying as a function of displacement of said second plate from said reference position; analog/pulse converter means connected to said displacement measuring means and having a converter output, for furnishing a sequence of pulses at said converter output, the number of pulses per unit time in said sequence of pulses varying as a function of said amplitude of said displacement signal; connecting means for connecting said converter output to said capacitor in such a manner that the electric force on said second plate created by said pulses opposes said force being measured; amplifier means having a predetermined amplification factor proportional to the amplitude of said pulses divided by said predetermined distance between said first and second plates connected to the output of said displacement measuring means; and switch means connected between the output of said amplifier means and said capacitor for connecting said output of said amplifier means to said capacitor in synchronism with the application of said pulses to said capacitor.

Claim 12

Force measuring apparatus comprising, in combination, a capacitor having a first plate and a second plate mounted parallel to said first plate in a reference position at a predetermined distance from said first plate and adapted to move in the direction perpendicular to said first plate under action of the force being measured; displacement measuring means connected to said capacitor for furnishing a displacement signal having an amplitude varying as a function of displacement of said second plate from said reference position; analog/pulse converter means connected to said displacement measuring means and having a converter output, for furnishing a sequence of pulses at said converter output, the number of pulses per unit time in said sequence of pulses varying as a function of said amplitude of said displacement signal; connecting means for connecting said converter output to said capacitor in such a manner that the electric force on said second plate created by said pulses opposes said force being measured; amplifier means having a predetermined amplification factor proportional to the amplitude of said pulses divided by said predetermined distance between said first and second plates connected to the output of said displacement measuring means; and switch means connected between the output of said amplifier means and said capacitor for connecting said output of said amplifier means to said capacitor in synchronism with the application of said pulses to said capacitor.