JPH0729456Y2 - Encoder circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an encoder circuit, and more particularly to an offset adjusting circuit of a magnetic encoder.

(Prior art) Encoders are absolute (absolute value) even during power failure
Some have a backup power supply so that the signal can be obtained. Although not yet published, the invention described in the specification and drawings of Japanese Patent Application No. 1-131119 relating to the application of the present applicant is an example thereof, and a circuit example thereof is shown in FIG. In FIG. 3, reference numeral 1 is a drive power supply, 2 is a backup power supply,
Reference numeral 3 is a sensor part of an encoder, 5 is an operational amplifier, 7 is a comparator, TR ₁ and TR ₂ are transistors, and R ₀ is a pull-up resistor. The sensor unit 3 always detects the position of the detected object of the encoder, for example, the magnetic drum, and outputs a signal. In the sensor unit 3, the magnetoresistive element MR ₁ , the transistor TR ₁ , and the resistor R ₄ are connected in series. The other magnetoresistive element, the transistor TR ₂ and the resistor R ₅ are connected in series, and the resistors R ₀₃ , R ₀₄ , and R ₀₅ are connected in series. A signal V ₁ is output from the magnetoresistive element MR _1, and a signal V ₂ is output from another magnetoresistive element. The constant current supply device for supplying a constant current I ₁ to the magnetoresistive element MR ₁ uses the drive power source 1 as a power source and applies a constant voltage Vr to the + terminal of the operational amplifier 5 via the Schottky diode CR ₃ and the resistor R ₀₄ . It has a constant current supply circuit 1 and a second constant current supply circuit by applying a constant voltage Vr to the negative terminal of the operational amplifier 5 via the resistors R ₀₃ and R ₀₄ using the backup power supply 2 as a power supply. The current I ₁ flowing through the magnetoresistive element MR ₁ is determined by I ₁ ≈Vr / R ₄ . Therefore, in the case of the second constant current supply circuit, since the resistor R ₀₃ is added as compared with the first constant current supply circuit, the voltage Vr applied to the + terminal of the operational amplifier 5 is increased.
Becomes smaller in the case of the second constant current supply circuit than in the case of the first constant current supply circuit, and a smaller constant current than that in the case of the first constant current supply circuit is supplied to the magnetoresistive element MR ₁ .

Now, assuming that the voltage applied to the + terminal of the operational amplifier 5 at the time of power failure is Vr ₁ and the voltage of the backup power supply 2 is Vb, the above voltage Vr ₁ is Vr ₁ = {R ₀₅ / (R ₀₃ + R ₀₄ + R ₀₅ )} × Vb. Further, when the voltage applied to the + terminal of the operational amplifier 5 at the normal time is Vr ₂ , the voltage Vr ₂ is Vr ₂ = {R ₀₅ / (R ₀₄ + R ₀₅ )} × (V ₅ −Vd ₂ ). Vd ₂ is the voltage across diode CR ₃ and is V ₅
−Vd ₂ is set to a value equal to or close to the voltage Vb of the backup power supply 2. Further, Vr ₂ is set to be several times higher than Vr ₁ so that a large current is passed through the magnetoresistive element MR ₁ .

As described above, since a large constant current is normally supplied to the magnetoresistive element MR ₁ by the first constant current supply circuit, a large detection signal V ₁ is output from the magnetoresistive element MR ₁ as shown in FIG. It Similarly, a large detection signal V ₂ is output from another magnetoresistive element. These large detection signals V ₁ , V
₂ is compared by the comparator 7 and output as an A-phase signal, and signal processing is performed such that it is counted by a counter (not shown), but a large detection signal
By obtaining V ₁ and V ₂ , the comparison operation by the comparator 7 becomes sharp and the frequency characteristic of the encoder can be improved.

On the other hand, during a power failure, the backup power supply 2 supplies a constant current smaller than the constant current supplied by the first constant current supply circuit from the second constant current supply circuit. Therefore, as shown in FIG. The signal is smaller than usual. However, during a power failure, the encoder output changes only when the object to be detected connected to the motor etc. rotates due to an external force.In this case, the rotation speed is slow and the encoder output also changes slowly. Even if the element outputs V ₁ and V ₂ are low and the encoder frequency characteristic is not good, it is possible to sufficiently cope with the situation. In FIG. 5, a curve I shows the waveform of the detection signal V _{1 in} the initial stage of backup, and a curve II shows the detection signal when the voltage of the power supply 2 drops at the end of the backup.
Waveforms of V ₁ are shown respectively.

As described above, according to the above-described example, since a sufficiently large constant current is normally supplied to the magnetoresistive element MR ₁ by the first constant current supply circuit, a sufficiently large signal V ₁ is output from the magnetoresistive element MR _1. The frequency characteristics of the encoder can be improved. Further, at the time of power failure, a constant current smaller than the constant current by the first constant current supply circuit is supplied from the backup power supply 2 to the magnetoresistive element MR ₁ through the second constant current supply circuit. Can be backed up over.

However, in the above example, the first has a first detector circuit having a first magnetoresistive element MR ₁ for obtaining a signal V _1, the second magnetoresistive element (not shown) for obtaining the signal V ₂ 2 There is no mention of adjustment of the offset between the detection circuit and the detection circuit.

Therefore, a circuit example as shown in FIG. 6 can be considered as a circuit example that enables the above-described offset adjustment. This uses a variable resistor VR ₃ as an adjusting means in place of the resistors R ₄ and R ₅ in the example of FIG. _3, and uses two transistors TR ₁ and TR ₂
Connect the emitter by a variable resistor VR _3, it is made by grounding the movable contact of the variable resistor VR _3. Therefore, the first magnetoresistive element MR ₁ , the transistor TR ₁ and the variable resistor VR ₃ are connected in series, and the second magnetoresistive element MR ₂ , the transistor TR ₂ and the variable resistor VR ₃ are connected in series. The comparator 8 is for obtaining a B-phase signal, and its input side is A
It is configured similarly to the circuit for obtaining the phase signals.

Now, if there is an offset between the first detection circuit having the first magnetoresistive element MR ₁ and the second detection circuit having the second magnetoresistive element MR ₂ , it is output from the comparator 7. The duty of the signal is deviated, and the position and moving direction of the detected object cannot be detected correctly. Therefore, in the example of FIG. 6, the variable resistor VR ₃ is adjusted to adjust the offset between the first detection circuit and the second detection circuit so that the above-mentioned inconvenience does not occur. .

(Problems to be Solved by the Invention) According to the example shown in FIG. 6, there are a normal operation by power supply from the drive power supply 1 and a backup operation by power supply from the backup power supply 2. The variable resistor VR ₃ does not make a distinction between offset adjustment for normal operation and offset adjustment for backup operation. Therefore, when the operation shifts to the backup operation while the offset is adjusted by the variable resistor VR ₃ during the normal operation, an offset deviation occurs due to the difference in the currents flowing through the two magnetoresistive elements MR ₁ and MR ₂ , so that the signal output from the comparator 7 The duty shifts and the position and moving direction of the detected object cannot be detected correctly.

The present invention has been made to solve the problems of the prior art, and enables the offset adjustment separately during both normal operation by the drive power supply and backup operation by the backup power supply for power failure. An object of the present invention is to provide an encoder circuit in which a duty shift of a signal does not occur when switching to a normal operation.

(Means for Solving the Problems) In the present invention, the sensor unit has a first detection circuit having a first magnetoresistive element and a second detection circuit having a second magnetoresistive element, and is a backup. First adjusting means for adjusting the offsets of the detection circuits when the power supply is in use,
A second means for adjusting the offsets of the detection circuits in the normal power supply operating state after the adjustment by the first adjusting means.
And the adjusting means of.

(Operation) The offset adjustment is performed by the first adjusting means in the use state of the backup power supply, and the first adjustment means does not change in the use state of the power supply for normal time, and the offset adjustment is performed only by the second adjustment means.

(Embodiment) An embodiment of an encoder circuit according to the present invention will be described below with reference to FIGS. 1 and 2. The third
Constituent parts common to the conventional example shown in FIGS. 6 and 6 are given common reference numerals, and only a brief description will be given, and different constituent parts will be mainly described.

In FIG. 1, reference numeral 1 is a power supply for normal time, 2 is a backup power supply for power failure, 5 is an operational amplifier, 7 is a comparator for A phase detection, 8 is a comparator for B phase detection, CR ₂ and CR ₃
Is a Schottky diode, TR ₁ and TR ₂ are NPN type transistors, MR ₁ is a first magnetoresistive element, MR ₂ is a second magnetoresistive element, and R ₀₃ , R ₀₄ , R ₀₅ , R ₆ are resistors, respectively. Show. The emitters of the two transistors TR ₁ and TR ₂ are connected to each other via a variable resistor VR ₁ forming a first adjusting means, and the movable contact of the variable resistor VR ₁ is grounded. The variable resistor VR ₁ corresponds to the variable resistor VR ₃ described in the conventional example of FIG. 6, and is for adjusting the offset in the usage state of the backup power supply 2. This embodiment differs from the conventional example shown in FIG. 6 in that a variable resistor VR ₂ and two PNPs as second adjusting means are used.
Type transistor TR _3, TR ₄ is added, the movable contact of the variable resistor VR ₂ is connected to the drive power supply 1 with an emitter cross of the two transistors TR _3, TR ₄ is connected by a variable resistor VR ₂ And also the above transistor TR ₃
Is connected to the emitter of the transistor TR _{1 and} the collector of the transistor TR _{4 to} the emitter of the transistor TR ₂ . The above two transistors TR ₃ , TR ₄
The output of the operational amplifier 5 is input to the base of R via the resistor R ₆ . The variable resistor VR ₂ is for adjusting the offset between the first and second detection circuits having the magnetoresistive elements MR ₁ and MR ₂ , and is the first adjustment without using the power supply 1. After performing the offset adjustment by the variable resistor VR ₁ which is the means, the offset is adjusted in the usage state of the power supply 1.

Now, when the power supply 1 is not operating, that is, when the current is not supplied from the power supply 1, the power is supplied from the backup power supply 2 such as a storage battery. In this state, as in the example of FIG. ₃ , no current flows through the diode CR ₃ and the voltage Vr
Since the value of is small, the current flowing through the magnetoresistive elements MR ₁ and MR ₂ is small. Also, the transistors TR ₃ and TR ₄ do not operate, and no current flows through the variable resistor VR ₂ . First in this state
The variable resistor VR ₁ as the adjusting means is adjusted to change the ratio of currents flowing through the first and second magnetoresistive elements MR ₁ and MR ₂ to perform offset adjustment.

When the power supply 1 is operating, a current is supplied from the power supply 1 via the Schottky diodes CR ₁ and CR ₂ and a current flows through the transistors TR ₃ and TR ₄ via the variable resistor VR ₃ . Further, during the normal operation in which power is supplied from the drive power source 1, as described in the example of FIG. 3,
The current flowing through the magnetoresistive elements MR ₁ and MR ₂ increases. In a normal operation state in which power is supplied from the drive power supply 1, the variable resistor VR ₂ which is the second adjusting means is adjusted to adjust the offset. At this time, the variable resistor VR ₁ is not changed.

In this way, when the backup power supply 2 is in use during a power failure, no current flows through the second variable resistor VR ₂ and the transistors TR ₃ and TR ₄ , so even if the variable resistor VR ₂ is adjusted, offset adjustment cannot be performed. , The offset can be adjusted by adjusting the _first variable resistor VR ₁ independently. When the drive power supply 1 is used after the offset adjustment by the _first variable resistor VR ₁ in this way, a current flows through the second variable resistor VR ₂ and the transistors TR ₃ , TR _4, and by adjusting the variable resistor VR ₂ . Since the ratio of the currents flowing through the two magnetoresistive elements MR ₁ and MR ₂ can be changed, the offset adjustment during normal operation can be performed by adjusting the variable resistance VR ₂ .

FIG. 2 shows another embodiment of the encoder circuit according to the present invention. This embodiment is different from the embodiment shown in FIG. 1 in that the transistors TR ₃ and TR ₄ in the embodiment shown in FIG. 1 are replaced with diodes D ₁ and D ₂ , respectively, and the operational effects are the same as those of the embodiment shown in FIG. The description is omitted because it is the same as the embodiment shown in the figure.

(Effect of the Invention) In the encoder circuit having the drive power supply and the backup power supply at the time of power failure, there is a difference in the amount of current flowing through the first and second detection circuits including the magnetoresistive element between the normal time and the power failure,
Although there is a difference in the offset amount between the normal time and the power failure, according to the present invention, the first adjusting means for adjusting the offset when the backup power source is used, and the drive power source after the adjustment by the first adjusting means are performed. Since the second adjusting means for adjusting the offset in the use state is provided, it is possible to adjust independently by the individual adjusting means in the normal time and the power failure, and the encoder output can be adjusted in the normal time and the power failure. Each can be stabilized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an encoder circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the encoder circuit according to the present invention, and FIG. 3 is an example of a conventional encoder circuit. Circuit diagram, FIG. 4 is a waveform diagram showing the output of the magnetoresistive element in the conventional case of the same as above, FIG. 5 is a waveform diagram showing the output of the magnetoresistive element in the same backup, and FIG. 6 is a conventional encoder circuit. 6 is a circuit diagram showing another example of FIG. 1 ... Normal power supply, 2 ... Backup power supply, MR ₁ ...
… First magnetoresistive element, MR ₂ … Second magnetoresistive element, V
R ₁ ... first adjusting means, VR ₂ ... second adjusting means.

Claims (1)

[Scope of utility model registration request] 1. An encoder circuit comprising a power supply for normal time and a backup power supply for power failure and counting a detection signal from a sensor section by a counter, wherein the sensor section has a first magnetoresistive element. A first adjusting circuit and a second detecting circuit having a second magnetoresistive element, and a first adjusting unit for adjusting an offset of the two detecting circuits in a state of using the backup power supply; An encoder circuit comprising: second adjusting means for adjusting the offsets of the detection circuits in the drive power source used state after the adjustment by the first adjusting means.