JPH0224286Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a detection circuit in a proximity switch.

A proximity switch such as a rotary encoder exists as a type of sensor that detects the amount of movement of an object. That is, the basic structure and operating principle of this type of proximity switch is as shown in FIG. , are arranged opposite to each other with the detection coil 3, and when a high frequency magnetic field is generated by the high frequency oscillation coil 2, an induced voltage whose amplitude is modulated by the slit position of the metal disk 1 is generated in the detection coil 3. . If this induced voltage is envelope-detected using an appropriate threshold voltage and further amplified, we get
You can get a square wave. FIG. 1B shows a block diagram of these. By counting these square waves, the amount of movement of the object can be detected. Incidentally, the phases of the rising edge and falling edge of this rectangular wave correspond to the position near the metal disk 1 having the slit, in other words, the position of the slit. In this case, if the power supply voltage applied to the circuit fluctuates for some reason, there is a problem in that the phases of the rising edge and the falling edge are shifted.

That is, FIG. 2 shows an example of the conventional oscillation circuit 4 and detection circuit 5 used in the above-mentioned proximity switch.
There is a disadvantage that when the voltage (voltage) fluctuates, the phases of the rising and falling edges of the rectangular waves appearing at the output terminals 6, 6' change, especially since there is no countermeasure against fluctuations in the power supply voltage in the circuit. In other words, this has the disadvantage that it may not be possible to accurately detect the amount of movement of the object, and the range of use is limited.

The present invention improves the above-mentioned drawbacks and provides a detection circuit for a proximity switch that minimizes the change in the phase of the rising and falling edges of a rectangular wave with a small number of circuit elements even if the power supply voltage fluctuates. This is the purpose.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a circuit according to an embodiment of the present invention, in which 4 is an oscillation circuit, L ₁ is an oscillation coil, and C _1
C3 is a capacitor, _R1 and _R2 are resistors, and these elements constitute a well-known Hartley type oscillation circuit. Further, 5 is a detection circuit, and L ₂ constituting this detection circuit 5 is a detection coil that forms a resonant circuit together with a capacitor C ₅ . Q ₂ is a detection transistor, and one end of a resonant circuit consisting of the detection coil L ₂ and capacitor C ₅ is connected to the base of this transistor Q ₂ , and the other end of this resonant circuit is connected to a diode D ₁ and a resistor R ₈ . A power supply voltage +V is applied through the resistor R11, and the other end is connected to the other end of a resistor _R11 whose one end is grounded. Also, the emitter of transistor Q ₂ has a resistor R ₄ ,
A voltage divided by R ₅ is applied, and a parallel circuit of a resistor F ₆ and a capacitor C ₄ is connected between the collector and ground. On the other hand, a capacitor _C6 is inserted between the connection point of the detection coil _L2 and the diode _D1 and the emitter, and the diode _D1 is forward-biased to the base of the transistor _Q2 . Also, transistor
_Q3 is an output transistor whose base is connected to the collector of transistor _Q2 via resistor _R9 , whose collector is connected to the power supply side via resistors _R10 and _R8 , and whose emitter is grounded.

FIG. 4 shows voltage waveforms at various parts. A is the oscillation voltage V _L1 caused by the oscillation coil L ₁ , B is the voltage V _L2 induced in the detection coil L ₂ , C is the envelope voltage V _R6 after detection,
D indicates the output pulse.

Next, the operation will be explained.

The induced voltage V _L2 amplitude-modulated by a metal disk with a slit is detected and amplified by the threshold voltage V TH (divided voltage V R4 of the power supply voltage + base-emitter voltage of transistor Q ₂ ), and then the voltage is amplified by the threshold voltage V _TH (divided voltage V _R4 of power supply voltage + base-emitter voltage of transistor Q 2). ₂
Appears on the collector side of This voltage is applied to the capacitor
It is smoothed by _C4 to obtain an envelope waveform voltage V _R6 .
This voltage V _R6 drives the output transistor Q ₃ and outputs a pulse voltage to its collector side. By the way, if the power supply voltage fluctuates (assuming it increases)
Then, the envelope waveform voltage V _R6 also changes, and when the power supply voltage fluctuates, the amplitude of the induced voltage V _L shown in B in FIG. 4 increases accordingly. In this state, the threshold voltage
If V _TH remains constant as shown by the solid or dashed line, the falling edge of the output pulse waveform will follow the dashed line.
As shown by A', the falling phase of the square wave pulse changes.

However, in the present invention, the transistor Q ₂
Since a divided voltage is applied to the voltage via the resistors R ₄ and R ₅ , when the power supply voltage changes, the change also appears in the voltage V _R4 , and this voltage is applied to the transistor Q ₂
Since the threshold voltage also changes according to the power supply voltage, as shown by the solid line B in Figure 4B, the edge of the output pulse follows it and becomes B', and the output pulse It is possible to reduce the phase change. Note that the output is positively fed back through the resistor _R10 , and a slight hysteresis is added to the switching operation of the circuit. Also, in Figure 3,
Capacitor _C6 is for high frequency bypass to avoid signal level reduction due to differential operation components. Furthermore, capacitor _C7 is to prevent residual high frequencies from appearing at the output. Also, diode _D1 is connected to the base of transistor _Q2 .
It performs temperature compensation between emitters and maintains the base potential of transistor _Q2 at a constant voltage during power supply fluctuations.
This serves to bias the variation between the base and emitter of transistor _Q2 .

In addition, in the above, it is also possible to use the one shown in FIG. 5 as the resonant circuit.

As described above, according to the present invention, which is inexpensive and configured using a relatively small number of circuit elements, when the power supply voltage fluctuates, the oscillation voltage V _L1 changes, and the detection voltage V _L2 changes accordingly. But in this case,
Since the threshold voltage is changed accordingly, it has an excellent effect of being able to compensate for changes in the pulse phase.

[Brief explanation of the drawing]

1A and 1B are explanatory diagrams showing the general configuration of a proximity switch, FIG. 2 is an example of a conventional detection circuit, FIG. 3 is a detection circuit of the present invention, and FIG. 4 is an explanatory diagram of the same operation. is the oscillation voltage V _L1 , B is the detection voltage V _L2 , C is the envelope detection voltage V _R6 , D is the output pulse, and FIG. 5 shows another embodiment of the resonant circuit. 5...Detection circuit, _Q1 to _Q3 ...Transistor,
L ₁ ...Oscillation coil, L ₂ ...Detection coil, D ₁ ...
Diode, R ₁ to R ₁₁ ... Resistor, C ₁ to C ₇ ... Capacitor.

Claims (1)

[Scope of utility model registration request] A high-frequency magnetic field is generated by the oscillation coil _L1 , and is transmitted through a rotating disk with many slits around the periphery.
In the proximity switch that detects the induced voltage using the detection coil _L2 that constitutes the detection circuit for the magnetic field, the detection coil that forms the resonant circuit on the detection circuit side.
Connect one end of L ₂ to the base of transistor Q ₂ ,
The other end of the detection coil is connected to the power supply side through a diode _D1 placed in the forward direction with respect to the base, and a resistor is connected between the power supply side and the ground side.
R ₄ and R ₅ are connected in series, the connection point between both resistors is connected to the emitter of transistor Q ₂ , the collector and ground point are connected to resistor R ₆ , and the connection point between the resonant circuit and diode D _{1 is connected to the emitter of transistor Q 2} . A capacitor _C6 is connected between the emitter of the transistor _Q2 and the collector of the transistor _Q2 is connected to the base of the output transistor _Q3 , and a square wave pulse is extracted at the output side of the output transistor _Q3 . Detection circuit in a proximity switch.