AUTOMATIC TOP-LOADING WEIGH APPARATUS WITH ELECTRONIC MEASURING AND RECORDING CIRCUIT

• US 3,604,525 A
• Filed: 08/15/1969
• Issued: 09/14/1971
• Est. Priority Date: 08/15/1969
• Status: Expired due to Term

• Current Assignee: Charles B. Blethen, James E. Smith
• Original Assignee: Charles B. Blethen, James E. Smith
• Inventors: Blethen, Charles B., Smith, James E.
• Primary Examiner(s): Wilkinson, Richard B.
• Assistant Examiner(s): Miller, Jr., George H.
• Application Number:
  US04/850,397
• Time in Patent Office: 760 Days
• Field of Search: 177/1,200,210,212,211
• US Class Current: 177/210.00R
• CPC Class Codes: G01G 7/04 with means for regulating the current to solenoids

Abstract

A top-loading weigh apparatus has a stabilized balance beam mechanism with the load being vertically applied through a horizontal balance arm on a pair of spaced pivots, and a differential capacitance is developed by sensing the horizontal displacement of a stabilized beam isolated from the weighing area. The capacitance developed in response to beam displacement is converted into a variable current output and applied as a restoring force proportional to but in opposition to the unbalancing force in order to quickly and accurately return the beam mechanism to its null position. A voltage is developed in direct proportion to the variable current output required to restore the beam to its null position and which is translated for recording and visual display of the applied weight.

Claims

1. In an automatic weigh balance having a balance beam wherein the load applied to the balance beam is measured by beam displacement from a null position, the improvement of:

variable capacitance means associated with said balance beam for measuring the displacement of said balance beam by a change in capacitance;

an AC signal source for generating an AC reference signal, said AC signal source being connected across said variable capacitance means to excite said capacitance means with said AC reference signal and generate an AC output representative of the change in the capacitance of said capacitance means;

trigger means connected to said AC signal source for generating trigger pulses from said AC reference signal at the instant the AC output of said capacitance means is only the capacitive component of said AC output, and circuit means connected to said variable capacitance means and selectively triggered by said trigger pulses for generating a DC signal proportional to the magnitude of said AC output at the instants said trigger pulses are generated whereby to generate a DC signal proportional onLy to the capacitive component of said AC output of said variable capacitive means thereby to reject the unwanted quadrature component of said AC output.

2. The invention recited in claim 1 wherein said variable capacitance means is a capacitive bridge having two legs of said bridge formed by variable capacitors, one plate of each of said variable capacitors being fixed relative to said balance beam and the other plate of each of said variable capacitors being connected to said balance beam for movement therewith whereby the deflection of said balance beam from its null position is measured by the change in capacitance of said variable capacitors, and including:

electrical null restoring means associated with said balance beam; and

means including an operational amplifier connected between said circuit means and said null restoring means for driving said null restoring means in response to the DC signal generated by said circuit means an amount proportional to beam displacement whereby to return said beam to its null position.

3. In an automatic top-loading balance apparatus, the combination comprising a frame, a balance beam mechanism including a stabilized vertical balance beam leg movable from a null position in response to variations in load applied to said balance beam mechanism, electromagnetic actuating means between said frame and said balance beam including relatively movable field and core members with at least one of said members having an excitable forcer coil, a capacitive bridge including a pair of fixed capacitors and a pair of variable capacitors, each of said variable capacitors having a frame-mounted capacitor plate and a capacitor plate movable with said beam leg and so arranged as to sense the direction and extent of movement of said beam leg in a positive or negative direction, oscillator means connected to said capacitive bridge for generating an AC reference signal and exciting said capacitive bridge therewith, differential amplifier means for measuring the differential increase and decrease in capacitance of said variable capacitors and for generating a sinusoidal wave form proportional thereto, a sampling circuit for sensing the amplitude and phase of each wave form generated by said differential amplifier, said sampling circuit being selectively triggered by the AC reference signal to develop a variable DC output as a function only of the direction and extent of balance beam movement as measured by the changes in the capacitance of said variable capacitors by sampling only the capacitive component of each wave generated by said differential amplifier means thereby to reject the unwanted quadrature component of each wave generated by said differential amplifier means, and means connected to said sampling circuit for receiving said DC output and exciting the forcer coil of said electromagnetic actuating means with a DC signal proportional to beam displacement whereby to return said balance beam to its null position.

4. In an automatic top-loading balance apparatus according to claim 3, further including a level detector in said sampling circuit operative to generate sampling pulses synchronous with the capacitive component of said sinusoidal wave form in response to the AC reference signal whereby to selectively trigger said sampling circuit whenever one of said sampling pulses is generated and develop said DC output.

5. In an automatic top-loading balance according to claim 4, wherein said means connected to said sampling circuit for receiving said DC output and exciting said forcer coil includes an operational amplifier having a frequency compensation network to drive said forcer coil negatively or positively according to the negative or positive condition of the variable DC output of said sampling circuit.

6. In an automatic weigh balance system, the combination comprising a frame, a balance beam mounted on the frame for limited mOvement from a null position in response to variations in applied load, electrical null restoring means associated with said balance beam, sensor means for sensing the beam position in response to variations in applied load including a pair of vehicle capacitors and an AC signal source connected across said variable capacitors to apply an AC reference signal thereto, each of said variable capacitors having a stationary capacitive sensor and a beam-mounted capacitive sensor so arranged as to differentially sense the direction and extent of balance beam movement by changes in their respective capacitances, differential amplifier means connected to said variable capacitors for differentially amplifying the AC signals generated across said variable capacitors by said AC signal source and for generating a differential AC output in response to the direction and extent of balance beam movement as measured by the changes in the capacitances of said variable capacitors, circuit means for generating a DC signal as a function only of the capacitive component of the differential AC output generated thereby to reject the unwanted quadrature component of the differential AC output, and means connected to the circuit means for receiving the DC signal generated by said circuit means and energizing said null restoring means an amount proportional to beam displacement whereby to return said beam to the null position.

7. In an automatic weigh balance system according to claim 1, wherein said AC signal source is an oscillator and further including a capacitive bridge, said bridge including said variable capacitors and a pair of fixed capacitors, and said capacitance bridge being interposed between said oscillator and said differential amplifier means.

8. In an automatic weigh balance system according to claim 6 wherein said stationary capacitive sensors are mounted on said frame in adjacent relation to one another and said beam-mounted capacitive sensors are disposed on opposite sides of said stationary capacitive sensors.

9. In an automatic weigh balance system according to claim 6, said electrical null restoring means being defined by electromagnetic actuating means having relatively movable field and core members with at least one of said members having an excitable forcer coil.

10. In an automatic weigh balance system according to claim 9, further including a reference circuit having a resistor in series with the said forcer coil to generate a voltage proportional to the signal applied to said forcer coil.