JPH0640802U - Proximity sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To enable accurate distance measurement even if the characteristics of the detection coil vary. [Configuration] The proximity sensor outputs a DC signal according to the distance to the measurement target 6 having conductivity. This sensor
Detection head 1 having detection coil 1a, and oscillation circuit 3
And a detection circuit 4. The oscillation circuit 3 includes a resistor R ₁ and capacitors C ₁ and C ₂ connected to the detection coil 1a, and the resistance value of the resistor R ₁ is variable so that the output amplitude can be changed. The detection circuit 4 DC-detects the output of the oscillation circuit 3 and outputs a detection signal.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a proximity sensor, and more particularly to a proximity sensor that outputs a direct current signal according to a distance to a measurement target having conductivity.

[0002]

[Prior art]

 For example, a linear output type proximity sensor that provides a voltage or current output proportional to the distance to a measurement target has a head having a detection coil and an amplifier body. The amplifier body has an oscillation circuit that generates an oscillation output with an amplitude that depends on the distance from the head to the measurement target, and a detection circuit that detects the oscillation output and outputs a curved DC voltage signal that depends on the distance. A linearization circuit that converts the detection output into a linearization signal proportional to the distance by a fixed function is provided.

In such a proximity sensor, the distance is measured by utilizing the fact that the oscillation amplitude of the oscillation circuit changes depending on the distance between the detection coil and the measurement target. In FIG. 5, which shows an equivalent circuit of the oscillation circuit of the proximity sensor, a capacitor C is connected to the detection coil L and a loss R exists as a resistance. Here, the relationship between the admittance Y and the conductance G is expressed by the following equation (1), the conductance G of the oscillation circuit changes according to the distance between the detection coil L and the measurement target, and further the admittance Y changes. To do.

[0004]

[Equation 1]

Here, the conductance G is the real part of the equation (1). Since the conductance G 1 changes according to the distance and the admittance Y changes according to the change in the conductance G, the distance from the detection coil to the measurement target can be measured by detecting the amplitude of the oscillation signal voltage.

[0006]

[Problems to be solved by the device]

 In the above-described conventional configuration, the characteristics of the change in conductance (that is, the characteristics of the change in oscillation amplitude with respect to the distance to the measurement target) change due to manufacturing variations in the detection head. If the characteristics of the change in the oscillation amplitude with respect to the distance to the measurement target change, the detection output obtained by detecting the oscillation output will have a different pattern. Since the detection output is linearized by a certain function in the linearization circuit, if the detection outputs of different patterns are given, the linearization cannot be performed accurately and the distance cannot be accurately measured.

An object of the present invention is to enable accurate distance measurement even if the characteristics of the detection head vary.

[0008]

[Means for Solving the Problems]

 The proximity sensor according to the present invention outputs a DC signal corresponding to the distance to the measurement target having conductivity. This sensor includes a detection head having a detection coil, an oscillation circuit and an output circuit. The oscillator circuit includes a resistor and a capacitor connected to the detection coil, and the resistance value of the resistor is variable so that the output characteristic can be changed. The output circuit DC-detects the oscillation output of the oscillator circuit and outputs a detection signal.

[0009]

[Action]

 In the proximity sensor according to the present invention, the detection head is arranged close to the measurement target. Then, the conductance changes according to the distance between the detection coil and the measurement target, and the oscillation amplitude of the oscillation circuit changes. A detection circuit detects this oscillation amplitude into a DC signal and outputs it. If the output of the detection circuit cannot be accurately linearized due to variations in the characteristics of the detection head, adjust the resistance value of the oscillator circuit resistance. As a result, the conductance in the oscillator circuit changes and the characteristic of the change in the output of the detection circuit with respect to the distance to the measurement target can be adjusted. Therefore, even if the characteristics of the detection head vary, an appropriate detection output can be obtained and accurate distance measurement can be performed.

[0010]

【Example】

 In FIG. 1, a proximity sensor according to an embodiment of the present invention comprises a detection head 1 arranged in proximity to a measurement target 6 and an amplifier main body 2 to which the detection head 1 can be attached / detached. A detection coil 1 a is arranged in the detection head 1. Note that d is the distance between the detection coil 1a and the measurement target 6. The amplifier main body 2 includes a Colpitts-collector grounded oscillation circuit 3 connected to the detection coil 1a, a detection circuit 4 that detects the output of the oscillation circuit 3 to obtain an S-shaped DC voltage signal, and a detection circuit 4 And a linearization circuit 5 which linearizes the DC voltage signal obtained in step 1 by a predetermined function and outputs the linearized signal.

The oscillator circuit 3 has a transistor Tr as shown in FIG. The base terminal of the transistor Tr is connected to the detection coil 1a and the variable resistor R₁, Capacity C₃And resistance R ₂ Connected through. Resistance R₁And capacity C₃A capacitor C connected in series is connected to the connection point between₁, C₂Are connected. Capacity C₁, C₂Is connected in parallel to the detection coil 1a and has a capacitance C₂Is grounded. Capacity C₁And capacity C₂At the connection point between₃The detection circuit 4 is connected via. Resistance R₃At the connection point between the detector circuit and the detector circuit 4, one end is grounded to a resistor R_FiveAnd the emitter terminal of the transistor Tr are connected. The power supply Vcc is connected to the collector terminal of the transistor Tr. Further resistance R₂The resistor R whose one end is grounded is connected to the connection point between the transistor and the base terminal of the transistor Tr._FourAre connected.

The resonance circuit constituted by the oscillation circuit 3 and the detection coil 1a configured as described above is substantially equivalent to the circuit shown in FIG. 5, and the conductance G in this case is also the real number of the equation (1). It is a department. Next, the operation of the above embodiment will be described. When the detection head 1 is arranged close to the measurement target 6, the conductance G of the resonance circuit changes according to the distance d. Therefore, since the admittance Y changes according to the equation (1), the amplitude of the oscillation circuit 3 changes. This amplitude is detected as a DC signal by the detection circuit 4, and an S-shaped detection output corresponding to the distance d as shown in FIG. 3 is obtained.

If the output obtained due to manufacturing variations of the detection head 1 cannot be accurately linearized, the variable resistor R ₁ is adjusted. For example, when an output shifted to the right as shown by the alternate long and short dash line is obtained as compared with the reference S-shaped amplitude change shown by the solid line in FIG. 3, by changing the resistance value of the variable resistor R ₁ , The rate of change indicated by the chain line approaches the rate of change indicated by the solid line. That is, even if the characteristics of the detection head 1 do not change, the conductance G can be set to an appropriate value by changing the value of the resistor R, and the output characteristics can be set to an appropriate state.

By changing and adjusting the resistance value of the resistor R ₁ as described above, it is possible to accurately obtain a linearized output corresponding to the distance. Other Embodiments (a) As shown in FIG. 4, instead of the resistor R ₁ , a variable resistor R ₆ may be inserted in series with the capacitors C ₁ and C ₂ . In this case, it is substantially the same as the equivalent circuit of FIG. 6, and the admittance Y is expressed by the following equation (2).

[0015]

[Equation 2]

Here, the real part of the equation (2) is the conductance G, and the increase or decrease of the conductance G can be adjusted by changing the value of the resistance Ra. Therefore, in the example shown in FIG. 4, by adjusting the resistance R ₆ to an appropriate value, it is possible to obtain a linearized output that accurately corresponds to the distance. (B) Instead of using a variable resistor, a resistor group having several kinds of resistance values may be inserted in series or in parallel with the detection coil L, and those resistance values may be selected by a switch or the like. Good. (C) The present invention can be applied to the case where the detection head and the amplifier main body are integrated. (D) Even in a Colpitts base grounding type or Hartley type oscillation circuit, the same effect can be obtained by inserting a resistor at an appropriate position.

[0017]

[Effect of device]

 In the proximity sensor according to the present invention, the oscillation amplitude can be adjusted by changing the resistance value, so that accurate distance measurement can be performed even if the characteristics of the detection head vary.

[Brief description of drawings]

FIG. 1 is a block diagram of a proximity switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of the oscillation circuit.

FIG. 3 is a graph showing the relationship between amplitude and distance.

FIG. 4 is an equivalent circuit diagram of the embodiment of FIG.

FIG. 5 is a diagram corresponding to FIG. 2 of another embodiment.

6 is an equivalent circuit diagram of the embodiment of FIG.

[Explanation of symbols]

1 Detection head 1a Detection coil 3 Oscillation circuit 4 Detection circuit R ₁ , R ₆ Variable resistance

Claims (1)

[Scope of utility model registration request] 1. A proximity sensor that outputs a DC signal according to a distance to a measurement object having conductivity, including a detection head having a detection coil, and a resistance and a capacitance connected to the detection coil, A proximity sensor, comprising: an oscillation circuit in which the resistance value of the resistor is variable so that the output characteristic can be changed; and an output circuit that outputs a detection signal by DC detection of the output of the oscillation circuit.