JPH1114352A - Current / frequency conversion circuit and tilt angle sensor including the circuit - Google Patents

Abstract

(57) [Problem] To provide a small-sized and high-precision tilt angle sensor capable of accurately measuring a minute change in a condensing position and accurately obtaining a tilt angle. The tilt angle sensor includes a container for holding a liquid having a free liquid surface, an irradiation unit for irradiating light to the liquid surface, and a light receiving unit for receiving light reflected from the liquid surface. ,
A current / frequency conversion circuit 7 for receiving a current signal from the light receiving means and outputting a pulse wave based on the input current; and a measuring means 8 'for measuring the frequency of the pulse wave output from the current / frequency conversion circuit. And a tilt angle calculator 8 for calculating a tilt angle based on the measured frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current / frequency conversion circuit and a tilt angle sensor provided with the current / frequency conversion circuit and suitably incorporated in a surveying instrument, a measuring instrument, or the like.

[0002]

2. Description of the Related Art Generally, a conventional liquid-surface reflection type inclination angle sensor has a structure as shown in FIG. That is, the light emitted from the light source 1 passes through the lens 2 to become parallel light, passes through the transparent liquid container 3, and enters the free liquid surface 3 'of a transparent liquid such as silicone oil.

[0003] The components 1 to 8 shown in FIG. 7 are integrally attached to instruments such as a surveying instrument and a measuring instrument (hereinafter simply referred to as a "surveying instrument"). The components also tilt. However, only the free liquid surface 3 ′ keeps a surface perpendicular to the direction of gravity, so that the angle at which light is incident on the free liquid surface 3 ′ and the angle at which the light is reflected are changed. The light position 4 changes according to the inclination angle. In other words, the inclination angle can be calculated from the information on the light condensing position 4. The light receiving element 5 is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-25664.
No. 7, JP-A-6-47813 discloses a line sensor. Therefore, the resolution is determined by the arrangement pitch of the line sensors, and only a low resolution can be obtained.

In a surveying instrument, the calculated inclination angle is used to correct a survey value of an altitude angle or a horizontal angle.

A conventional example of another condensing position detecting means for obtaining high resolution will be described with reference to FIG. 4 light receiving elements
Using a divided sensor, a difference between output currents from each sensor is converted into a voltage difference by a current / voltage conversion circuit, and the converted voltage is converted into a digital value by an A / D conversion circuit, and then a predetermined calculation is performed by an arithmetic circuit. By doing so, the inclination angle could be measured.

[0006]

In the prior art as shown in FIG. 7, since the change in the condensing position on the light receiving surface due to the inclination angle is small, the distance from the free liquid surface 3 'to the light receiving surface is increased. By doing so, the ratio of the change of the condensing position to the change of the angle is increased. However, by increasing the distance from the free liquid surface 3 'to the light receiving surface, the configuration scale of the tilt angle sensor becomes large, and the tilt angle sensor cannot be applied to a surveying instrument requiring a small size as a whole configuration. was there.

Alternatively, in the prior art shown in FIG. 8, since the change in the light condensing position on the light receiving surface due to the inclination angle is very small, the received light current signal is converted into a voltage with high accuracy in order to accurately detect the angle change. Since it is necessary to read the minute voltage change with high accuracy by the A / D conversion circuit, a high resolution and high accuracy A / D conversion circuit is required. Such high resolution A /
D-conversion circuits are expensive, and the circuit scale is large, so that the package size is large and the power consumption is large.
For this reason, if the tilt angle sensor is configured by the current / voltage conversion circuit and the A / D conversion circuit, the configuration becomes complicated, the cost increases, and a surveying instrument requiring small size, light weight, and low power consumption is required. There was also a problem that it could not be realized.

Further, when the power supply voltage to the A / D conversion circuit fluctuates, the reference voltage serving as the reference for A / D conversion fluctuates, and as a result, an error occurs in the A / D converted output. there were. In order to solve this problem, an input current is converted into a frequency and detected. However, as shown in FIG. 9, a current / voltage conversion circuit and a voltage / frequency conversion circuit are combined. Needed a large circuit.

An object of the present invention is to provide a current / frequency conversion circuit capable of performing current / frequency conversion with a simple circuit, capable of measuring a minute change in a light-collecting position with high accuracy, being compact, and having low power consumption. An object of the present invention is to provide a tilt angle sensor that can accurately determine the tilt angle of a surveying instrument.

[0010]

In order to solve the above-mentioned problems, a current / frequency conversion circuit according to the present invention comprises an amplifying means for amplifying an input current, a voltage based on the amplified current being input, and the input voltage being equal to the input voltage. When the first input voltage is reached, the first output voltage changes to the second output voltage. When the second input voltage is reached, the second output voltage changes to the first output voltage. Output control means for outputting a voltage, and voltage changing means for changing the input voltage between a first input voltage and a second input voltage for a time corresponding to the magnitude of the input current. And the output voltage of the output control means changes between the first output voltage and the second output voltage in response to the change in the input voltage, whereby the input current is reduced to the magnitude of the input current. It is converted to a pulse wave of the corresponding frequency and output. The features.

According to the present invention, the input voltage input to the output control means changes between the first input voltage and the second input voltage by the voltage changing means, so that the output voltage output from the output control means is changed. The voltage changes to a first output voltage and a second output voltage in accordance with the change in the input voltage, and the input current is converted into a pulse wave having a frequency corresponding to the magnitude of the input current. In this case, the minimum resolution of the current / frequency conversion circuit is determined by the current frequency conversion coefficient (output frequency / input current) of the circuit. By setting the conversion coefficient high, the resolution can be increased and the dynamic range can be increased. A circuit that is wide, has excellent linearity, and has a desired minimum resolution can be realized with a simple circuit configuration.

In this case, the voltage changing means changes the input voltage so that the period when the output voltage is the first output voltage is shorter than the period when the output voltage is the second output voltage. A pulse wave having a frequency based on the current is output.

[0013] The voltage changing means may include discharging means through which the amplified current flows, feedback means for returning a part of the output of the output control means to the input side, and electricity storage means for accumulating the electric charge based on the input voltage. And can be configured.

In this case, the input voltage may be gradually reduced by the discharging means and rapidly increased by the feedback means and the power storage means.

Further, the tilt angle sensor according to the present invention comprises a container for holding a liquid having a free liquid surface, an irradiating means for irradiating the liquid surface with light, and a light receiving means for receiving light reflected from the liquid surface. A current / frequency conversion circuit for receiving a current signal from the light receiving means and outputting a pulse wave based on the input current; and measuring a frequency of the pulse wave output from the current / frequency conversion circuit. And a tilt angle calculator for calculating a tilt angle based on the measured frequency.

According to the present invention, the amount of movement of the reflected light from the liquid surface on the light receiving surface of the light receiving means based on the inclination of the inclination angle sensor is small, so that the change of the current signal from the light receiving means is small. As described above, a pulse wave having a frequency corresponding to the minute current can be output by the high-resolution current / frequency conversion circuit as described above. A change in a minute current can be detected. This makes it possible to accurately measure a minute change in the light condensing position on the light receiving surface of the light receiving unit. In addition, it is not necessary to increase the distance from the free liquid surface of the container to the light receiving surface of the light receiving means in order to increase the amount of movement on the light receiving surface of the light receiving means, so that the configuration of the tilt angle sensor can be reduced in size. Becomes

The light receiving means may have a plurality of divided light receiving surfaces, and may further include a signal selection circuit for time-dividing a current signal from each of the divided light receiving surfaces.

According to this configuration, even if a plurality of current signals are output from the light receiving means, the plurality of current signals can be time-divided and input to the current / frequency conversion circuit.
The frequency conversion can be performed by the two current / frequency conversion circuits, and the adjustment of the conversion characteristics unique to the circuit becomes unnecessary, and the circuit configuration of the tilt angle sensor can be simplified.

Further, the light receiving means has a light receiving surface divided into four, and the signal selection circuit is provided with four light receiving surfaces from each of the light receiving surfaces.
Two of the current signals may be combined and added, and the obtained four sum signals may be input to the current / frequency conversion circuit in time series.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of the current / frequency conversion circuit according to the present embodiment. FIG.
FIG. 2 is a diagram for explaining the circuit operation of FIG. The current / frequency conversion circuit shown in FIG. 1 has an operational amplifier U in which a circuit input terminal 21 and a resistor R1 are connected to a non-inverting input terminal (+).
1, an output terminal of the operational amplifier U1 is connected to the base of the transistor Q1, and an inverting input terminal of the operational amplifier U1 (-).
And a resistor R connected to the emitter of the transistor Q1.
2, a Schmitt trigger inverter U2 having an input terminal connected to the collector of the transistor Q1 and an output terminal connected to the circuit output terminal 22, and a Schmitt trigger inverter U2.
And a diode D1 connected in series with the resistor R3 between the input terminal and the output terminal of the Schmitt trigger inverter U2.

FIG. 3 shows a Schmitt trigger inverter U2.
FIG. 3 is a diagram schematically showing a relationship between an input voltage and an output voltage of FIG. When the input voltage changes between the voltages 1 and h in the direction of the arrow in the figure, the output voltage changes between the voltages L and H as shown by the arrow, forming a hysteresis loop as shown in the figure.

The operation of the current / frequency conversion circuit shown in FIG. 1 will be described. Input current I1 from circuit input terminal 21
Is amplified by the operational amplifier U1 and the transistor Q1, and the amplified current I2 flows through the collector of the transistor Q1. The current amplification factor in this case is determined by the resistances of the resistors R1 and R1.
The current I2 is determined by a ratio (R1 / R2) to the current I2.
It can be represented by the following equation (1).

I2 = (R1 / R2) × I1 (1) Since the charge stored in the capacitor C1 is discharged as a current I2 via a resistor R2 whose other end is grounded, the voltage of the capacitor C1 (Schmitt trigger) The input voltage of the inverter U2) gradually decreases with time as between a and b shown in FIG. The output voltage of the Schmitt trigger inverter U2 at this time is a low voltage value L as shown in FIG. 2 (b), and even if there is a feedback circuit including the resistor R3 and the diode D1, the output voltage of the capacitor C1 is not affected. Do not give.

When the voltage of the capacitor C1 continues to decrease and reaches the low voltage value 1 at the point b in FIG. 2A, the output voltage of the Schmitt trigger inverter U2 becomes as shown in FIG. 2B and FIG. Then, a transition is made from the low voltage value L to the high voltage value H. At this time, the output voltage of the Schmitt trigger inverter U2 becomes higher than the voltage value of the capacitor C1,
The diode D1 is in a forward-biased state, and the output voltage of the Schmitt trigger inverter U2 is fed back through the feedback circuit of the diode D1 and the resistor R3, so that charge is rapidly accumulated in the capacitor C1. As a result, the voltage value of the capacitor C1 sharply rises between b and c shown in FIG.

When the voltage of the capacitor C1 rises sharply and reaches the high voltage value h at the point c in FIG. 2A, the output voltage of the Schmitt trigger inverter U2 becomes as shown in FIGS. 2B and 3. , Transition from H to L. Thus, the time between b and c depends on the Schmitt trigger inverter U
2 corresponds to the period in which the output voltage of the high voltage value H is the high voltage value H,
The time is shortened by the operation of the feedback circuits D1 and R3 as compared with the time between them. For this reason, the output voltage of the Schmitt trigger inverter U2 shows a pulse waveform. At this time, the output voltage of the Schmitt trigger inverter U2 is
1, the diode D1 is in a reverse-biased state, does not affect the voltage value of the capacitor C1, and the voltage of the capacitor C1 is equal to a in FIG.
As in the case of ~ b, it decreases with time. Circuit input terminal 2
The above operation is repeated while the input current I1 flows through the circuit 1, and a pulse wave from the Schmitt trigger inverter U2 is output to the circuit output terminal 22.

By the way, when the voltage of the capacitor C1 is
(A) Time t from the start of descent from point a to point b
Is determined by the current I2. That is, if the amount of current of I2 is large, the time t becomes short, and if the amount of current of I2 is small, the time t becomes long.

A short time t means that the output pulse interval is short, so that the frequency is high. A long time t means that the output pulse interval is long, so that the frequency is low. Therefore, the frequency of the output pulse wave changes according to the magnitude of the input current amount. In this case, the transmission frequency f of the output pulse wave from the circuit output terminal 22 can be expressed by the following equation (2).

F = {I2 / (hysteresis width of U2 × C1)} + (2 × R3 × C1) (2) As described above, the current I2 obtained by amplifying the current I1 input to the circuit input terminal is the capacitor By the action of C1, the Schmitt trigger inverter U2, the resistor R3, and the diode D1, it is converted into a pulse wave having a certain frequency, and current / frequency conversion can be realized.

Since the minimum resolution of the current / frequency conversion circuit is determined by the current / frequency conversion coefficient of the circuit represented by the transmission frequency f of the pulse wave in Equation 2, the circuit constants C1, R3 and the like are appropriately selected. By setting the coefficient in, the resolution can be increased. As a result, FIG.
The current / frequency conversion circuit shown in (1) has a wide dynamic range, is excellent in linearity, and can have a desired minimum resolution. Therefore, the target minimum resolution can be easily achieved in the tilt angle sensor only by configuring a counter for frequency measurement as post-processing as described later.

Next, an inclination angle sensor according to an embodiment of the present invention will be described. FIG. 4 is a block diagram illustrating a configuration of the tilt angle sensor according to the present embodiment, and includes the current / frequency conversion circuit illustrated in FIG. The tilt angle sensor illustrated in FIG. 4 includes a sensor unit and a block A that is a measurement processing unit, and is configured as a biaxial tilt angle sensor that can measure a tilt angle in an arbitrary direction on the XY plane.

As shown in FIG. 4, the sensor section has the same structure as the optical system shown in FIG.
A liquid container 3 containing a light-transmissive liquid such as silicone oil and having a free liquid surface 3 'and a bottom portion formed of a light-transmissive member is provided with a light-receiving element 5. As shown in FIG. 5, the light receiving element 5 is formed of a photoelectric converter whose light receiving surface is equally divided into four, and includes light receiving surfaces PD1, PD2, PD3, and PD4.

The block A of the measurement processing section controls the signal selection circuit 6, the current / frequency conversion circuit 7, the counter 8 'for counting the number of pulses from this circuit 7, and the signal selection circuit 6 to calculate the tilt angle. Angle calculator 8 for calculating the inclination angle.

The signal selection circuit 6 receives the input current from the photoelectric converter on each of the light receiving surfaces PD1 to PD4 of the four-divided light receiving element 5,
It can be arbitrarily selected under the control of the inclination angle calculator 8. The plurality of selected input currents are time-divided and input to the input terminal 21 of the current / frequency conversion circuit 7.

As the current / frequency conversion circuit 7, the one shown in FIG. 1 can be used, and a pulse wave output therefrom according to the input current is input from the output terminal 22 to the counter 8 '. The frequency is measured by counting the number of pulse waves in the counter 8 ', and the inclination angle is calculated in the inclination angle calculation unit 8 based on the measured frequency information.
Thus, in the measurement processing section A shown in FIG.
By reading the change in the amount of current output from each of the light receiving surfaces PD1 to PD4, the light condensing position 4 is recognized, and the tilt angle of the tilt angle sensor can be obtained.

The operation of the tilt angle sensor configured as described above will be described. The light emitted from the light emitting element 1 passes through the lens 2 to become parallel light, and the liquid container 3 having a light-transmitting bottom portion.
And enters the free liquid surface 3 ′ of the translucent liquid. Since the components 1 to 8 shown in FIG. 4 are integrally attached to the surveying instrument, when the surveying instrument tilts, the components also tilt by the same amount. However, only the free liquid surface 3 ′ maintains a surface perpendicular to the direction of gravity, so that light from the light emitting element 1 is
The angle of incidence and the angle of reflection change, resulting in
The light condensing position 4 on the light receiving surfaces PD1 to PD4 of the light receiving element 5 changes according to the inclination angle.

FIG. 5 shows the light receiving surfaces PD1 to PD of the light receiving element 5.
FIG. 9 is a plan view of D4, showing light receiving surfaces PD1 to P of light receiving element 5;
The arrangement of D4 is shown by the relationship in the XY directions. As shown in FIG.
When the light collected on the light receiving surface is at the position of the circle a, the inclination angle sensor is horizontal in the X direction and the Y direction. here,
For example, when the tilt angle sensor is tilted in the direction of the arrow X, the condensing position on the light receiving surface of the light receiving element 5 moves from the position of the circle a to the position of the circle b shown by the broken line,
The focusing position moves from the position of the circle a to the position of the circle c. The X-direction tilt information can be represented by a ratio between a predetermined current difference and a current sum, and the Y-direction tilt information can be represented by another predetermined current difference and a current sum.

That is, the light receiving surfaces PD1 to PD of the light receiving element 5
The outputs of the respective photoelectric converters 4 are input to a signal selection circuit 6, which selects a light receiving signal from an arbitrary light receiving surface under the control of the inclination angle calculation unit 8, and outputs the four input signals. Four sum signals obtained by combining two currents (hereinafter, these input currents are referred to as “PD1 + PD2”,
“PD3 + PD4”, “PD1 + PD4”, “PD2 +
PD3 ". ), PD1 + PD2, PD3 + PD
4, PD1 + PD4 and PD2 + PD3 are input to the current / frequency conversion circuit 7 in this order.

Subsequently, in the current / frequency conversion circuit 7, four input currents PD1 + PD2, PD3 + PD4,
PD1 + PD4, PD2 + PD3 are converted into pulse waves having frequencies F1, F2, F3, and F4 respectively corresponding to these input currents, and output to the pulse counter 8 'in time series. This relationship is schematically shown in FIG.

The pulse counter 8 'counts the number of pulses during a certain period of time, and measures the frequencies F1, F2, F3 and F4 corresponding to each input current from the counted value. Tilt angle calculator 8
FIG. 6 is based on the frequency information obtained by the counter 8 '.
The light-condensing position (x, y) is obtained from Expressions 3 and 4 shown in the following expression, and the inclination angle is calculated.

In the above configuration, since the signal from the light receiving surface of the light receiving element is input to the current / frequency conversion circuit 7 in a time division manner by the signal selection circuit 6, the current / frequency conversion can be performed even if the four-division light receiving element 5 is used. The number of circuits may be a minimum number, for example, one circuit. Compared to the case where a plurality of current / frequency conversion circuits are used, it is difficult to adjust them with a plurality of circuits because the difference between the conversion characteristics can be an error, whereas in the case of one circuit, The inherent conversion characteristic is canceled by the calculation in the inclination angle calculation unit (Equation (3),
In addition, the circuit configuration can be simplified by using the minimum number of circuits. In addition, a small, highly accurate, and stable tilt angle sensor can be provided.

As described above, the current / frequency conversion circuit 7
It is known that the circuit constants C1, R can greatly change the output frequency in response to a minute current change of the current signal as the input signal.
It becomes possible by selecting 3 or the like. Therefore, the inclination angle calculator 8
Can be recognized as a difference in the number of pulses, that is, a digital value, even if the change is slight.

Since the output of the current / frequency conversion circuit 7 is a pulse train, the resolution of the pulse count is determined by the counter 8 '.
It is possible to increase the operation speed up to. Regarding this resolution, it is possible to obtain sufficient performance at the operating speed of the normal logic element or the counter of the arithmetic element that performs the tilt angle calculation. The current / frequency conversion circuit 7 in the present embodiment
It outperforms general performance in terms of resolution as compared with the A / D converter.

Further, by using the current / frequency conversion circuit, the inclination angle information at the output does not depend on the power supply voltage as in the conventional circuit configuration shown in FIG. Enables power consumption,
It is easy to interface with the inclination angle calculation unit 8 in accordance with the power supply voltage.

In the tilt angle sensor according to the present embodiment,
Although a four-divided light receiving element is used, the present invention is not limited to this, and a two-divided sensor can be used. In this case, a uniaxial tilt angle sensor capable of measuring a tilt angle in one direction is configured. it can. Further, a three-division sensor can be used, and a two-axis inclination angle sensor can be configured by causing the inclination angle calculation unit 8 to perform an appropriate operation.

[0045]

According to the present invention, it is possible to provide a current / frequency conversion circuit capable of performing current / frequency conversion with a simple circuit configuration and having high resolution.

Further, according to the tilt angle sensor of the present invention provided with the above current / frequency conversion circuit, it is possible to measure a small change in the condensing position with high accuracy and accurately obtain the tilt angle. An accurate tilt angle sensor can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a current / frequency conversion circuit according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams for explaining the operation of the current / frequency conversion circuit shown in FIG. 1; FIG. 2A is a diagram showing a time change of a voltage of a capacitor C1 (input voltage of a Schmitt trigger inverter U2); FIG. 9B is a diagram illustrating a time change of the output voltage of U2.

FIG. 3 is a diagram schematically showing a relationship between an input voltage and an output voltage of Schmitt trigger inverter U2 shown in FIG.

FIG. 4 is a circuit block diagram showing a configuration of the tilt angle sensor according to the embodiment of the present invention.

FIG. 5 is a plan view for explaining a change in a light condensing position on a light receiving surface of the light receiving element shown in FIG.

6 is a diagram for explaining an example of a sequence in which a tilt angle calculation unit in the tilt angle sensor shown in FIG. 4 controls a signal selection circuit and a change example of an output frequency.

FIG. 7 is a diagram showing a configuration of a conventional inclination angle sensor.

FIG. 8 is a diagram showing a circuit configuration of a conventional tilt angle sensor.

FIG. 9 is a diagram showing a circuit configuration of another conventional tilt angle sensor.

[Explanation of symbols]

 U1 Operational amplifier Q1 Transistor C1 Capacitor U2 Schmitt trigger inverter D1 Diode R1 to R3 Resistance 1 Light emitting element 2 Lens 3 Liquid container (oil case) 3 'Free liquid surface 4 Focusing position 5 Four-division light receiving element PD1 to PD4 Light receiving element 5 Divided light receiving surface 6 Signal selection circuit 7 Current / frequency conversion circuit 8 Tilt angle calculator 8 'Counter 21 Input terminal 22 Output terminal

Claims (6)

[Claims] Amplifying means for amplifying an input current; a voltage based on the amplified current being input;
When the input voltage reaches the first input voltage, the output voltage changes from the first output voltage to the second output voltage. When the input voltage reaches the second input voltage, the output voltage changes from the second output voltage to the first output voltage. Output control means for outputting a voltage, and voltage changing means for changing the input voltage between a first input voltage and a second input voltage for a time corresponding to the magnitude of the input current, When the output voltage of the output control means changes between the first output voltage and the second output voltage in response to the change in the input voltage, the input current has a frequency corresponding to the magnitude of the input current. A current / frequency conversion circuit, which is converted into a pulse wave and output. 2. The voltage changing means includes a discharging means through which the amplified current flows, a feedback means for returning a part of an output of the output control means to an input side, and a power storage means for accumulating charges by the input voltage. 2. The method according to claim 1, further comprising:
The current / frequency conversion circuit according to any one of the preceding claims. 3. The current / frequency conversion circuit according to claim 2, wherein said input voltage changes by decreasing by said discharging means and increasing by said feedback means and said power storage means. 4. A container for holding a liquid having a free liquid level, irradiation means for irradiating the liquid surface with light, light receiving means for receiving light reflected from the liquid surface, and a current signal from the light receiving means 4. A current / frequency conversion circuit according to claim 1, 2 or 3, wherein a pulse wave is output based on the input current, and for measuring a frequency of the pulse wave output from the current / frequency conversion circuit. A tilt angle sensor comprising: a measuring unit; and a tilt angle calculation unit that calculates a tilt angle based on the measured frequency. 5. The light receiving means has a plurality of divided light receiving surfaces, and further comprises a signal selection circuit for time-dividing a current signal from each of the divided light receiving surfaces. The tilt angle sensor according to any one of the preceding claims. 6. The light receiving means has a light receiving surface divided into four, and the signal selection circuit is obtained by combining and adding two of four current signals from each of the light receiving surfaces. 4
The tilt angle sensor according to claim 5, wherein two sum signals are input to the current / frequency conversion circuit in a time series.