JPS58601B2 - length measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an element (hereinafter referred to as a conversion resistor) that converts an angular displacement into a change in electrical resistance value.

This invention relates to a length measuring instrument that digitally displays measured values using a resistance-pulse width conversion circuit that converts the resistance value of ) into a pulse width.

FIG. 1 is a diagram showing a measuring instrument conventionally used to measure the length of certain body parts such as the head and chest of a newborn baby.

In FIG. 1, L1. L2 is an arm, M is a scale plate engraved with a distance scale between the tips of the arms proportional to the angle between the arms, P is the fulcrum, and D is the distance between the tips of the arms.

In the conventional measuring instrument shown in Fig. 1, one end of two arms L1 and L2 intersect, the intersection is set as a fulcrum P, one arm L2 is fixed to a scale plate M, and the other arm L1 is set as a fulcrum P. It is configured so that it can rotate around the scale plate M
The rotation angle of arm L1 is arm L1. A length scale proportional to the angle is engraved to indicate the distance between the tips of L2.

In this conventional measuring instrument, there is a restriction on the pinch of the scale when marking the length proportional to the angle on the scale plate M (arm L
1. Since the opening angle of L2 and the distance between its tips are sinusoidally proportional, the scale pitches of the scale plate M are not equally spaced and it is difficult to make accurate markings.

), it is not possible to measure very accurately, and the engraved symbols are generally small, resulting in the inconvenience of misreading the measured values.

The present invention has been made in view of this point, and its purpose is to obtain a length measuring instrument that can digitally display measured values. Using a resistance-pulse width conversion circuit that converts the resistance value into a displacement, and further converts the electric resistance value displacement into a pulse width displacement, the distance between the ends of the arms is measured by the time width according to the pulse width, and the measured value is calculated. Displayed digitally.

The present invention will be described in detail below using the drawings.

Fig. 2 is a block diagram of the first embodiment of the present invention showing the main parts as a circuit diagram, Figs. 3 and 4 are circuit diagrams showing a part of Fig. 2, and Fig. 5 is a block diagram of the first embodiment of the invention. FIG. 4 is a time chart showing voltage change points between a and b with respect to on/off of the switching element 5; FIG. 6 is a block diagram of a second embodiment of the present invention showing the main parts as a circuit diagram; FIG. 7 is a time chart explaining the operation of the second embodiment.

First, a first embodiment of the present invention will be described with reference to FIGS. 2 to 5.

In Fig. 2, 1 is a DC power supply with a voltage of E volts, 2 is a DC amplifier, 3 is a voltage-controlled pulse width modulator whose pulse width changes according to the input voltage, and 4 is a pulse width modulator 3. oscillator for driving; 5 is a switching element, which is a transistor in the embodiment; 6 is a frequency divider; 7 is a gate; 8 is a counter; 9 is a display; 10 is a conversion resistor whose resistance value is R1 (variable); 14 is a fixed resistor with a resistance value of R2-R5, and 15 is a capacitor with a capacitance of C.

The conversion resistor 10 has a rotating shaft fixed to the fulcrum of the arm, and a third
As shown in the figure, a variable resistor 101 whose resistance value changes linearly in proportion to the angle between the two arms (the total resistance value is RV, and the resistance value when it changes in proportion to the opening degree of the arms is R8
shall be.

) and a resistance value R in parallel with the total resistance of this variable resistor 101.
It is composed of the effective resistance value between one connection point c' and the sliding terminal d when the fixed resistors 102 of No. 7 are connected.

That is, the resistance value R1 of the conversion resistor 10 is a composite resistance value of the resistance value R8, the resistance value (RV-R8), and the resistance value R7,
Its value is .

This resistance value R1 is a quadratic function whose variable is a resistance value R8 that changes in proportion to the rotation angle of the rotation shaft of the variable resistor 101.

On the other hand, when one end of two arms of constant length l intersect and the intersection is used as a fulcrum, one arm is fixed and the other arm is rotated, the angle between the arms is θ (of the arm to be rotated). The rotation axis of the variable resistor 101 is fixed at the center of rotation, and this angle θ is
Corresponds to the rotation angle of the rotation axis of 1.

), then the distance between the tips of the two arms that are not used as fulcrums is, and this distance is a trigonometric function with the angle θ as a variable.

In the present invention, the angle θ in equation (2) is set to 10 degrees≦θ≦90, for example.
The total resistance RV of the variable resistor 101 and the fixed resistance are adjusted such that the parabola of the quadratic function of the above equation (1) approximately corresponds to the sine characteristic indicated by the distance when the distance is changed within the range of A value of 102 resistance values R7 is set.

The table below shows an example of the degree of approximation of the quadratic interval of equation (1) to ideal sine characteristics.

In this table, the total resistance value RV of variable resistor 101 is set to 10Ω.
, when the resistance value R7 of the fixed resistor 102 is set to 13.3Ω and the rotation axis of the variable resistor 101 is rotated by 60 degrees, that is, when the resistance value R8 is approximately 1.67Ω, the ideal sine characteristic is obtained. The comparison is made so that they match, and the constant A of the ideal sine characteristic at this time is 3.094.

As can be seen from this table, the conversion resistance 10 when the rotating shaft of the variable resistor 101 rotates within an angle range of 10 degrees to 90 degrees
The resistance value R1 is obtained within an error range of 2% of the ideal resistance value Rx.

Since variable resistors with sinusoidal characteristics are not generally available, a variable resistor with linear characteristics is used to approximate the sinusoidal characteristics. If a variable resistor whose resistance value changes at Needless to say, there is no need for parallel connection (parallel connection).

The conversion resistance 10 set as above is the fixed resistance 1
1 to 14 constitute a bridge circuit.

The oscillator 4 generates a signal with a constant frequency f, and the frequency divider 6 transmits the signal with a frequency f from the oscillator 4 to the m pulse width modulator 3.
is driven by this signal with a constant period T, and sends out a pulse with a period T (constant) and a pulse width t (varies depending on the output of the DC amplifier 2 as described later).

The above-mentioned pulse from the pulse width modulator 3 is supplied between the base and emitter of the transistor 5, which is a switching element, and the transistor 5 is turned on only for a time t, as shown in FIG. The switching operation is performed so as to turn off only during the period T-t).

FIG. 4 is a diagram for considering the current due to the switching operation of the transistor 5. The switching operation of the transistor 5 repeatedly charges and discharges the capacitor 15, and in FIG. (discussed excluding the resistance 13 of the inter-bridge) has a substantially triangular shape obtained by integrating a rectangular wave as shown in the opening of FIG.

In this case, if the time constant determined by the product of the capacitance C of the capacitor 15 and the resistance value R5 of the resistor 14 is selected to be sufficiently larger than the repetition period T of the pulse from the pulse width modulator 3,
The voltage between them is sufficiently smoothed to become a substantially constant voltage Ec.

Current i flowing through resistor 14 while transistor 5 is on
2 is 12=Ec/R because the voltage between a and b is Ec
5......(3).

Also, in Fig. 4, the resistor 1 passes through the resistor 14 and the transistor 5.
If the average current appearing at 2 is i1, then i.T=i2.t, so 12=i1.T/l (4).

From equations (3) and (4), Ec/11=R5・T/l (5) is obtained, where Ec is the voltage between a and b, and i1 is the resistance 14
Since this can be regarded as the effective current passing through the branch of transistor 5, Ec/i1 in equation (5) represents the effective resistance of this branch,
Let this be Rt.

Rt=R5・T/l (6) That is, if the period T is constant, the effective resistance Rt of the branch including the transistor 5 is inversely proportional to the time t that the transistor 5 is on. However, this ON time t is related to the value indicated by the conversion resistor 10.

In FIG. 2, it is assumed that the equilibrium state of the bridge circuit constituted by the conversion resistor 10 and the fixed resistors 11 to 13 is disrupted, and a voltage Vi is output at point c.

The output voltage Vi of the bridge circuit is amplified by a DC amplifier 2, and the amplified output voltage is inputted to a pulse width modulator 3, and is converted into a pulse train supplied from an oscillator 4 via a frequency divider 6. The pulse width of is changed in accordance with the output of the DC amplifier 2.

The pulse train subjected to pulse width modulation in this manner is input to the transistor 5, and the transistor 5 is repeatedly turned on and off according to the input pulse train, thereby controlling the effective resistance value R1 of the branch including the transistor 5 in FIG. do.

The pulse width modulator 3 is configured such that when the input voltage changes in the direction of decreasing (increasing), the pulse width of the output pulse train changes in the increasing (decreasing) direction. 6) From the relationship in equation 4, the effective resistance value Rt of the branch including transistor 5 in FIG. 4 decreases (increases).
change in the direction of

Now, when the arm is opened and the resistance value R1 of the conversion resistor 10 changes in the direction of increasing, the output voltage of the bridge circuit V
1 changes in the direction of decreasing.

This output voltage Vi is amplified by a DC amplifier 2 and inputted to a pulse width modulator 3, which changes the pulse width t of the output pulse in the direction of increasing it.

That is, when the resistance value R1 of the conversion resistor 10 increases,
When the effective resistance Rt of the branch including the transistor 5 in FIG.
1 becomes larger and the bridge circuit becomes balanced.

In this way, the bridge circuit always maintains a nearly balanced state,
An output is obtained from the pulse width modulator 3 in which the pulse width t corresponding to the magnitude of the resistance value R1 of the conversion resistor 10 changes.

Furthermore, if the polarity of the DC power source of the bridge circuit is connected in the opposite direction to that shown in FIG. The configuration is such that the pulse width t increases.

With this configuration, when the resistance value R1 of the conversion resistor 10 changes in an increasing (decreasing) direction, the output voltage Vi of the bridge circuit changes in an increasing (decreasing) direction, and the output pulse of the pulse width conversion circuit 3 changes. Since the width t changes in the increasing (decreasing) direction, the effective resistance value Rt of the branch including the transistor 5 in FIG. 4 eventually changes in the decreasing (increasing) direction, and the bridge circuit becomes in an equilibrium state.

When this bridge circuit is in a substantially balanced state, if the amplification degree of the DC amplifier 2 is made sufficiently large, for example, 90 dB, the output V1 of the bridge circuit becomes extremely small, and the bridge circuit can be completely balanced. .

In this case, in the bridge circuit shown in FIG. 2, if the combined resistance value between a and b is Ra, the following relationship holds true as is generally known.

R2・R3=R1・Ra From this relationship, the combined resistance value Ra of the branch including the transistor 5 of the bridge circuit is the effective resistance value Rt between a and b explained with reference to FIG. 4, and the resistance value R4 of the fixed resistor 13. is the combined resistance value when are connected in parallel, and the following relationship holds true.

becomes.

From equations (7) and (8), the following relationship holds true when the bridge circuit is approximately balanced.

When the pulse width t is determined from equation (9), as is clear from the relationship shown in equation (10), the pulse width t of the pulse output from the pulse modulator 3 is proportional to the resistance value R1 of the conversion resistor 10.

The relationship between the resistance value R1 of the conversion resistor 10 and the pulse width t is related only to the resistance configuring the bridge circuit and the pulse repetition period T.
If the pulse width t is configured to be constant, the pulse width t is related only to the change in the resistance value R1 of the conversion resistor 10, and is unrelated to the voltage E of the DC power supply 1 of the bridge circuit.

By the way, as described above, the pulse width modulator 3 is driven at every constant period T after dividing the signal of constant frequency f from the oscillator 4 into m by the frequency divider 6.

This period T is expressed by .

On the other hand, a pulse with a pulse width t sent out from the pulse width modulator 3 is input to the gate 7, which opens the gate 7, and supplies the pulse from the oscillator 4 to the counter 8 only during the period when the gate 7 is open. The counter 8 counts the number of pulses supplied.

If the counter 8 counts the number of pulses n, then
The pulse width t of the pulse from the pulse width modulator 3 is expressed as t.

The relationships from equations (10), (11), and (12) hold, and from this, the number n of pulses counted by the counter 8 is determined as follows.

As is clear from the relationship in equation (13), the count value n of the counter 8 is proportional to the resistance value R1 of the conversion resistor 10.

Also, the relationship (13) is for anonymous numbers m and n, resistance value R1 ~
It is related only to R5 and is unrelated to voltage fluctuations and frequency fluctuations, and will continue to be unaffected by external conditions such as voltage fluctuations and frequency fluctuations.

Here, the resistance value R1 of the conversion resistor 10 is a quadratic function whose variable is the resistance value R8, which changes linearly in proportion to the angle θ between the two arms, as shown in equation (1) above, and is limited to The conversion resistor 10 is connected to the variable resistor 101 and the fixed resistor R7 so that the change in resistance value R1 approximates the change in the sine value of the trigonometric function within the range of the elongation.
Therefore, the change in the pulse width t of the pulse output from the pulse modulator 3 is relatively approximated to the change in the sine value of the trigonometric function.

Therefore, the change in the count value n counted by the counter 8 during the pulse width t is approximately proportional to the change in the sine value of the trigonometric function whose variable is the angle θ between the two arms.

And if the distance between the two arm tips is D,
By configuring the circuit of the counter 8 so that the count value n of the counter 8 at the angle between the two arms (the angle of the rotation axis of the variable resistor 101) θ at that time corresponds to the above distance, The count value of the counter 8 can be made to correspond to the distance between the arms within a limited angle.

The count value n counted by the counter 8 in this manner is input to the display 9, and its contents, that is, the distance to be measured, is displayed on the display 9.

Next, a second embodiment will be explained with reference to FIGS. 6 and 7.

In the first embodiment described above, the pulse width-to-resistance converter is composed of a resistor, a capacitor, and a switching element (transistor), but in the second embodiment described below, the DC amplifier 2 is This is an example in which the amplifier is configured to perform the same operation as the first embodiment.

In FIG. 6, 21 is an operational amplifier, 22 is an impedance for feedback, the other impedances for feedback are the same as in FIG. 2, and the others are the same as in FIG. 2.

Further, FIG. 1 shows waveforms at points A, B, and C shown in FIG. 6.

The operational amplifier 21 may be of a known type, and the connection point between the resistors 11, 13 and 14 is connected to the negative input (-) of the operational amplifier 21.
and connect the connection point of conversion resistor 10 and resistor 12 to the positive input (
+), and the output voltage is fed back to the negative input (-) via the feedback impedance 22.

When a capacitive element such as a capacitor is used as the feedback impedance 22, the DC amplifier 2 becomes a Miller integrator as is well known, and the slope of its output is determined by the feedback impedance 22 and the impedance of the bridge circuit. It changes according to a fixed time constant and the potential difference between the positive input (+) and the negative input (-).

Further, in this second embodiment, the pulse width modulator 3 is constituted by a flip-flop circuit, and the flip-flop circuit is set by a pulse output from the frequency divider 6 at a constant period T, and the operational amplifier 21 is connected to be reset when the output of the flip-flop circuit reaches a reset threshold level Eth of the flip-flop circuit.

By the way, in the bridge circuit of the second embodiment, the resistors 11,
The voltage at the connection point a between the converting resistor 10 and the resistor 12 is slightly lower than the voltage at the connecting point d between the conversion resistor 10 and the resistor 12 when the transistor 5 is on, that is, when the resistor 14 is connected in parallel with the resistor 13. When the resistor 14 is off, that is, the resistor 14 is not connected in parallel with the resistor 13, it is set slightly higher.

That is, if we consider when the transistor 5 is off, the voltage at point d is lower than the voltage at point a, so the operational amplifier 21
Since its positive input (+) becomes lower than its negative input (-), its output decreases.

As in the first embodiment described above, when the pulse from the frequency divider is input to the pulse width modulator 3, the output of the pulse width modulator is inverted, which turns on the transistor 5 and changes the point a of the bridge circuit. voltage becomes lower than the voltage at point d, the positive input (+) of the operational amplifier 21 becomes higher than the negative input (-), and the output is between the positive input (+) and the negative input (-). , that is, the potential difference between point a and point d of the bridge circuit.

When the output of the operational amplifier 21 reaches the reset threshold level Eth of the pulse width modulator 3, the output of the pulse width modulator 3 is inverted again and returns to the original state, which turns off the transistor 5, so that the bridge The voltage at point a of the circuit becomes higher than the voltage at point d again, and the positive input (+) of the operational amplifier 21 becomes lower than the negative input (-), and its output is divided between the positive input (+) and negative input (-). -), that is, the potential difference between points a and d of the bridge circuit.

Then, when a pulse is supplied from the frequency divider 6 again, the pulse width modulator 3 inverts its output, the transistor 5 is turned on again, and the above operation is performed, and from then on, the pulse width modulator 3 is output from the frequency divider 6. The above operation is repeated each time.

By the way, in the above operation, the voltage at point d of the bridge circuit changes depending on the resistance value R1 of the conversion resistor 10, which changes with a substantially sinusoidal characteristic according to the opening angle of the two arms, so the positive and negative values of the operational amplifier 21 change accordingly. The input potential difference also changes, and the rising slope of the output of the operational amplifier 21 changes according to the change in the potential difference, and the pulse width t of the output pulse from the pulse width modulator 3 eventually becomes the resistance value R of the conversion resistor 10.
Follows changes in 1.

In this way, the resistor 14 is connected between a and b of the bridge circuit via the transistor 5 which is turned on according to the pulse width t of the output pulse from the pulse width modulator 3, so that the resistor 14 is connected between a and b of the bridge circuit.
The combined resistance value Ra between
and the period T of the output pulse from the frequency divider 6, and the bridge circuit is balanced based on this resistance value Ra.

The output pulse with the pulse width t outputted from the pulse width modulator 3 as described above is input to the gate 7, and this time t
During this period, the gate 7 is opened, the signal from the oscillator 4 is guided to the counter 8, and the measured value is displayed on the display 9 based on the signal, as in the first embodiment.

In the first and second embodiments described above, the switching element (transistor) 5 is inserted on the opposite side of the conversion resistor 10, but the switching element 5 may be placed on the adjacent side of the conversion resistor 10. In this case, the resistance value R1 of the conversion resistor 10 and the pulse width t of the output pulse of the pulse width modulator 3 have an inversely proportional relationship.

That is, for example, in the first embodiment shown in FIG.
When either the resistor 11 or the resistor 12 is used as a conversion resistor, when the resistance value R2 or R3 of the conversion resistor 11 or 12 changes in the lower direction (higher direction) from the relationship in equation (10), the pulse width t is large (small)
Become.

Therefore, when the switching element (transistor) 5 is placed adjacent to the conversion resistor in this way, the change in the opening angle of the two arms and the change in the resistance value of the conversion resistor are inversely proportional to each other. That is, the resistance value of the conversion resistor is set so as to decrease (increase) as the opening angle of the arm increases (decreases).

Further, in the embodiment, when a transistor is used as the switching element 5, an example is shown in which the emitter is grounded, but it is clear that the present invention can be practiced with any grounding method.

As explained in detail above, in the present invention, the bridge circuit is always operated in the direction of a balanced state by the negative feedback loop, and the magnitude of the feedback adjustment amount is converted into a pulse width within this negative feedback loop, and the pulse width is The degree of the external element that acted to shift the bridge circuit to an unbalanced state by the amount of feedback adjustment obtained by changing the width, that is, in this example, the resistance value of the conversion resistor, that is, the angle between the two arms According to the circuit configured in this way, there is almost no influence from external conditions such as fluctuations in the power supply of the bridge circuit or environmental temperature, and highly accurate measurement is possible.

In addition, since the conversion resistor uses a variable resistor with sine characteristics or a variable resistor with linear characteristics whose characteristics are approximated to approximately sine characteristics by an external fixed resistor, the distance between the two arm tips is Since the distance between the two and the change in the resistance value of the conversion resistor is accurately proportional within an extremely small error range, accurate length measurement is possible.

Further, the present invention is advantageous in terms of power consumption because the measurement is performed with the bridge circuit in a substantially balanced state.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing one example of a length measuring instrument currently in use, Fig. 2 is a block diagram showing the main part of the first embodiment of the present invention as a circuit diagram, Figs. The figure is a partial circuit diagram of FIG. 2, FIG. 5 is a time chart of the first embodiment, FIG. 6 is a block diagram showing the main part of the second embodiment of the present invention as a circuit diagram, and FIG. is a time chart of the second embodiment. Main symbols, 2...DC amplifier, 3...
・Pulse modulator, 4... Oscillator, 5...
・Switching element (transistor), 6...
Frequency divider, 10... Conversion resistor, 11 to 14
, 102...Fixed resistor, 15.22...
...Capacitor, 101...Variable resistor.

Claims (1)

[Claims] 1. Length measurement in which the distance between a pair of tips on the opposite side of the fulcrum of two arms that open and close using one end as a fulcrum is determined by the opening angle of the two arms. In the device, (A) a conversion resistor whose resistance value changes according to the opening and closing of two arms; (B) a circuit network having a switching element and whose effective resistance value is determined by the average conduction time of the switching element; (C) a bridge circuit in which the conversion resistor is connected in parallel on one side and the circuit network is connected in parallel on the other side; a pulse width modulator that outputs a pulse width modulator, which changes the effective resistance value of the circuit network in a direction in which the bridge circuit is balanced by the unbalanced output of the bridge circuit caused by the change in the resistance value of the conversion resistor; A length measuring instrument characterized in that the distance between a pair of tips of the two arms on the opposite side from the fulcrum is detected based on the output pulse width of the pulse modulator. 2. The length measuring instrument according to claim 1, wherein the conversion resistor is a variable resistor whose resistance value changes sinusoidally with respect to the rotation angle of the rotating shaft. 3. The conversion resistor is comprised of a variable resistor whose resistance value changes linearly with respect to the rotation angle of the rotating shaft, and a fixed resistor connected in parallel to the total resistance value of the variable resistor. A length measuring instrument according to claim 1. 4. The circuit network includes a switching element that repeats on and off with the output pulse of a pulse width modulator whose output pulse width changes depending on the output voltage of the bridge circuit, a resistance element connected in series with the switching element, and the above-mentioned switching element. 2. The length measuring instrument according to claim 1, comprising a series circuit of a resistance element and a capacitive element connected in parallel. 5. The circuit network includes a Miller integrator that receives the output voltage of the bridge circuit as an input, a switching element that repeats on and off with the output pulse of a pulse width modulator whose pulse width changes according to the output of the Miller integrator, and the switching element. 2. The length measuring instrument according to claim 1, comprising a resistance element connected in series with the length measuring element.