JPH0829113A - Signal processing circuit for position sensor - Google Patents

Abstract

PURPOSE:To provide a signal processing circuit for a position sensor for extending the life of a slide resistor by suppressing the generation of a slide noise attributed to wear dust of a resistor and changes in output voltage characteristics. CONSTITUTION:A signal processing circuit 20 is made up of resistors 21, 22 and 23, an operational amplifier 24 and a changeover switch 25. The resistor 21 functions as pullup resistance when the changeover switch 25 is turned to the position (a) and the resistor 22 functions as pulldown resistance when the changeover switch 25 is turned to position (b). When a sensor section 10 is used, a brush slides on a resistor section 11 with the rotation of a rotor while a resistance value of a contact resistor section 12 changes by a wear dust generated by a friction between the brush and the resistor section 11 to generate a slide noise. To correct changes in the upper side output and the lower side output of a sensor output voltage as caused by the slide noise, the resistor 21 and the resistor 22 are used to calculate a resistance value of the contact resistor section 12 and the sensor output voltage containing no slide noise with an arithmetic section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a position sensor, and more particularly to a signal processing circuit for a position sensor using a resistance type sliding sensor.

[0002]

2. Description of the Related Art A position sensor using a resistor type sliding sensor is provided with a sliding resistor composed of a printed resistor and a brush sliding on the resistor, and is proportional to the sliding amount of the brush. Then, the resistance value of the sliding resistor changes. This type of position sensor is used for an accelerator position sensor that detects the depression angle of the accelerator pedal of an automobile, a throttle position sensor that detects the opening of a throttle valve, and the like, and detects the voltage applied to the resistor of a sliding resistor. The angle or opening is detected by outputting from the brush as an output voltage that changes in proportion to the accelerator pedal depression angle or the throttle opening.

However, in a position sensor using such a sliding resistor, abrasion resistance is generated due to abrasion and abrasion of the resistor itself due to repeated friction when the brush slides and the like. Since it easily intervenes with the resistor, there is a problem that sliding noise is generated and output characteristics are changed. Further, there is a problem that the life of the sliding resistor itself is shortened due to the excessive wear of the resistor.

Therefore, in an accelerator position sensor, a throttle position sensor, etc. of an automobile, which is required to be safe, a method of detecting the expiration of the life of a sliding resistor is required in advance, for example, Japanese Unexamined Patent Publication No. 4-240504. There is a contact sensor disclosed in. According to this method, the concentrated contact resistance value is provided with the measuring means for measuring the concentrated contact resistance with respect to the brush on the resistor and the judging means for judging whether or not the concentrated contact resistance is within the allowable range of the predetermined level. When it is out of the allowable range, after confirming that the number of times of measurement satisfies a predetermined condition, the abnormality determining means and the warning output means inform that the concentrated contact resistance is abnormal.

[0005]

However, according to the contact sensor disclosed in Japanese Unexamined Patent Publication No. 4-240504, a method of directly measuring the concentrated contact resistance as described above and determining the presence / absence of abnormality by various determining means. Has a problem that it is difficult to set an allowable range of a predetermined level of the concentrated contact resistance because the concentrated contact resistance greatly changes due to the influence of temperature, humidity and the like depending on the usage environment of the contact sensor. Further, since this contact sensor is composed of the concentrated contact resistance measuring means, the judging means, the abnormality judging means, the warning output means, the output voltage measuring means, etc., the circuit configuration for embodying these various judging means becomes complicated. Therefore, there is a problem that the cost is increased.

The present invention has been made to solve such a problem, and suppresses the generation of sliding noise and the change of output voltage characteristics due to the abrasion powder of the resistor, thereby extending the life of the sliding resistor. An object of the present invention is to provide a signal processing circuit for a position sensor.

[0007]

A signal processing circuit for a position sensor according to claim 1 according to the present invention for solving the above-mentioned problems, wherein a voltage is applied to one electrode and the other electrode is connected to a reference potential. A resistor, a contact portion having an output terminal that slides on the resistor and outputs a voltage correlated to a sliding position with reference to the reference potential, and a common terminal connected to the output terminal. A contact switching unit whose common terminal is connected to one of the contacts; a first resistor connected between one contact of the contact switching unit and an electrode at one end of the resistor; A second resistor connected between the other contact of the switching means and the electrode at the other end of the resistor, and one of the contact switching means depending on the output voltage output from the output terminal. Switch to the contact and change the output voltage to the first Characterized in that it comprises a control means for applying the anti-vessel or said second resistor.

A signal processing circuit for a position sensor according to a second aspect of the present invention is the signal processing circuit for a position sensor according to the first aspect, which includes the first resistor and the second resistor. The circuit is provided with the contact switching means. The signal processing circuit of the position sensor according to claim 3 of the present invention is the signal processing circuit of the position sensor according to claim 1 or 2, wherein the control means applies the first resistor to the first resistor. And the voltage Vp applied to the second resistor by the control means.
It is characterized by further comprising a calculating means for calculating a resistance value of a contact resistance generated between the resistor and the contact portion according to d.

According to a fourth aspect of the present invention, there is provided the signal processing circuit of the position sensor according to the third aspect, wherein the arithmetic means is based on a potential difference between the voltage Vp and the voltage Vd. The resistance value of the contact resistance is calculated. The signal processing circuit of the position sensor according to claim 5 of the present invention is the signal processing circuit of the position sensor according to claim 3 or 4, wherein the arithmetic means corrects the output voltage from the resistance value of the contact resistance. It is characterized by doing.

A signal processing circuit for a position sensor according to a sixth aspect of the present invention is the signal processing circuit for a position sensor according to the third, fourth or fifth aspect, wherein the arithmetic means is output from the output terminal. It is characterized by comprising a signal converter for converting an output voltage into a digital signal and an arithmetic unit for arithmetically processing the digital signal output from the signal converter.

[0011]

According to the signal processing circuit of the position sensor of the present invention, the output voltage is corrected from the resistance value of the contact resistance measured by the calculating means, so that the sliding noise caused by the abrasion powder of the resistor is generated. Moreover, there is an effect that the change of the output voltage characteristic is suppressed and the life of the resistor is extended.

Further, according to the signal processing circuit of the position sensor of the present invention, the resistance value of the contact resistance is measured by the switching means for switching between the first resistor and the second resistor according to the output voltage of the contact portion. Therefore, there is an effect that a circuit including the first resistor, the second resistor, and the contact switching means can be simply configured. Further, according to the signal processing circuit of the position sensor of the present invention, a circuit including the first resistor, the second resistor, and the contact switching means can be configured with a small number of parts, so that the failure occurrence rate can be reduced. And the cost can be reduced.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A first embodiment in which the position sensor signal processing circuit of the present invention is applied to a position sensor signal processing system is shown in FIG.
~ Shown in FIG.

As shown in FIG. 2, the position sensor signal processing system comprises a sensor section 10, a signal processing circuit 20, an A / D converter 30 and an arithmetic unit 31. The signal processing circuit 20 detects sliding noise of the output voltage V1 output from the sensor unit 10 including a sliding resistor, and the detected voltage V2
Is converted into a digital signal V3 by the A / D converter 30. After the arithmetic operation is performed by the arithmetic unit 40 from the digital signal V3 and each known data to correct the sliding noise, the sensor output voltage Vx containing no sliding noise is obtained.

The sensor portion 10 is composed of a resistor portion 11 printed in an Ω shape on a substrate (not shown) and a brush (not shown) connected to a rotor (not shown) rotatable within an angular range of, for example, 125 °. ing. This brush is a contact portion that slides on the surface of the resistor portion 11, and is electrically connected to the surface of the resistor portion 11 via contact resistance. FIG.
An equivalent circuit of the sensor unit 10 is shown in FIG. The equivalent circuit of the sensor unit 10 is composed of a resistor unit 11 and a contact resistor unit 12 generated between the brush sliding on the surface of the resistor unit 11 and the resistor unit 11. One terminal of the resistor portion 11 is connected to the terminal Vcc and a power supply voltage is applied. Since the other terminal of the resistor portion 11 is connected to the reference potential E, a voltage proportional to the rotation angle of the rotor is output from the terminal V1 via the contact resistor portion 12 of the brush.

The signal processing circuit 20 includes resistors 21, 22,
23, an operational amplifier 24, and a changeover switch 25. The resistor 21 is connected between the terminal a and the terminal Vcc, which is connected to the common terminal when the changeover switch 25 is turned to the a side, and functions as a pull-up resistor. Also resistor 2
2 is connected between a terminal b and a terminal E, which are connected to a common terminal when the changeover switch 25 is tilted to the side b, and functions as a pull-down resistor. Further, the resistor 23 is connected between the terminal c and the terminal E, which are connected to the common terminal when the changeover switch 25 is neutralized to the neutral point, and functions as a protective resistance. The resistance values of the resistors 21 and 22 are determined by the power supply voltage connected to the terminal Vcc and the resolution of the A / D converter 30. For example, the resistors 21 and 22 may have the same resistance value, the power supply voltage is, for example, 5 V, and the A / D converter 30.
When the resolution of is 16 bits, for example, about 100 kΩ is preferable. The resistor 23 is a protection resistor provided to prevent the non-inverting input terminal of the operational amplifier 24 from being opened when the sensor unit 10 is disconnected.
The resistance value is set to a level that does not affect the input voltage of. The common terminal of the changeover switch 25 connected to the terminal V1 of the sensor section 10 is connected to the non-inverting input terminal of the operational amplifier 24. The inverting input terminal of the operational amplifier 24 is connected to the output terminal of the operational amplifier 24 connected to the terminal V2 to form an impedance conversion circuit.

When the sensor portion 10 is used, a brush (not shown) slides on the resistor portion 11 as the rotor (not shown) rotates. At this time, due to repeated friction between the brush and the resistor portion 11, the resistor portion 11 itself is scraped off and abraded, so that abrasion powder is generated. The abrasion powder changes the resistance value of the contact resistor portion 12 to generate sliding noise. As shown in FIG. 4, this sliding noise changes the sensor output voltage of the sensor unit 10 and causes an upper output fluctuation 52 and a lower output fluctuation 53. Therefore, the upper output fluctuation 52 and the lower output fluctuation 5
3 causes the sensor output voltage 51 under normal conditions to fluctuate up and down. In the present invention, this upper output fluctuation 52,
In order to correct the lower output fluctuation 53, the resistance value of the contact resistance part 12 is calculated using the resistors 21 and 22 described above, and the sensor output voltage that does not include sliding noise is calculated.

Now, the calculation of the resistance value of the contact resistance portion 12 and the sensor output voltage not including the sliding noise will be described. When the changeover switch 25 is tilted to the a side, the terminal V1 of the sensor section 10 is connected to the resistor 21 to form the equivalent circuit shown in FIG. At this time, the output voltage Vp of the terminal V2 is expressed by the following equation (1).

Vp = (Va × Rp + Vcc × Rc) / (Rp + Rc) (1) where Vp: output voltage (V) of terminal V2 Va: output voltage (V) of terminal V1 Vcc: power supply voltage ( V) Rp: resistance value of the resistor 21 (Ω) Rc: resistance value of the contact resistor portion 12 (Ω) When the changeover switch 25 is tilted to the b side, the sensor portion 1
The terminal V1 of 0 is connected to the resistor 22 to form the equivalent circuit shown in FIG. At this time, the output voltage of the terminal V2 is expressed by the following equation (2).

Vd = Va × Rd / (Rc + Rd) (2) where Vd: output voltage (V) of terminal V2 Va: output voltage (V) of terminal V1 Rd: resistance value of resistor 22 ( Ω) Rc: Resistance value (Ω) of the contact resistance portion 12 Further, Rp and Rd are arbitrary values, and if Rp = Rd = R as described above, then equations (1) and (2) are obtained. Than R
c is led.

Rc = (Vp−Vd) × R / [Vcc− (Vp−Vd)] (3) (Vp−Vd) shown in the equation (3) is the changeover switch 2
5 is the voltage of the terminal V1 of the sensor unit 10 when the switch is moved to the side a, minus the voltage of the terminal V1 of the sensor unit 10 when the changeover switch 25 is moved to the side b, and R and Vcc
Is a constant that is determined by the power supply voltage and the resolution of the A / D converter 30 as described later, and therefore the resistance value Rc of the contact resistor portion 12 can be calculated by the equation (3).

Here, the relationship between the resistance value Rc of the contact resistance portion 12 and the resolution of the A / D converter 30 will be described.
When (Vp-Vd) shown in the equation (3) is replaced with ΔV, the equation (3) is transformed into the equation (4). This ΔV corresponds to the minimum resolution of 1 LSB of the A / D converter 30. Rc = ΔV / (Vcc−ΔV) × R (4) For example, when R is 100 kΩ, power supply voltage Vcc is 5 V, and resolution of the A / D converter 30 is 16 bits,
The minimum resolution of 1 LSB is 1.5Ω. However, since the accuracy of the A / D converter is generally about ± 2 LSB, ± 3.
An accuracy of 0Ω will be obtained.

Furthermore, by modifying the equation (2) and calculating Rc, the sensor output voltage Vx containing no sliding noise.
Can be calculated. Vx = (Rc + Rd) × Vd / Rd (5) With this equation (5), the sensor output voltage Vx that does not include sliding noise, that is, the corrected sensor output voltage Vx can be obtained. The resistance value Rc of the contact resistance part 12 and the sensor output voltage V that does not include sliding noise that can be calculated from the above-described calculation formula.
x can be calculated by using the A / D converter 30 and the calculator 31 shown in FIG.

In the first embodiment, the position sensor signal processing system does not always operate, but an external activation factor such as, for example, an operator's activation instruction, an operation start or an operation end of a device including the position sensor signal processing system, etc. Operated by. The operation of the position sensor signal processing system will be described based on the flow chart shown in FIG.

The control program of the arithmetic unit 30 is activated by an external activation factor. In step 71, the changeover switch 25 of the signal processing circuit 20 is changed over to the a side, and the terminal V
Connect 1 to resistor 21 to pull up the sensor output voltage. The output voltage V2 at this time is A /
Measured through the D converter 30 and set to Vp. Next, at step 73, the changeover switch 25 of the signal processing circuit 20 is changed over to the b side, the terminal V1 is connected to the resistor 22 and the sensor output voltage is pulled down. The output voltage V2 at this time is measured through the A / D converter 30 in step 74 as in step 72, and is set to Vd. Vp and Vd measured in steps 72 and 74, resistors 21, 22
Substituting the actual resistance value R and the actual power supply voltage Vcc into the equation (3), the resistance value Rc of the contact resistance portion 12 is calculated in step 75. Further, in step 76, this Vd, the resistance value Rc of the contact resistance portion 12 and the actual resistance value R of the resistor 22 are substituted into the above equation (5) to calculate the corrected sensor output voltage Vx. In order to protect the operational amplifier 24 in case of disconnection of the sensor section 10, the changeover switch 25 is controlled to connect the terminal V1 to the changeover resistor 23 to the side c which is the middle point, and the program is terminated at step 77.

Next, a comparative example will be described with reference to FIG. 6 in order to clarify the effect of the first embodiment. The signal processing circuit 33 of this comparative example includes a constant current source 34, changeover switches 36, 37, 38, 39 which are interlocked with each other and an operational amplifier 24.
It consists of and. When an abnormality or the like occurs in the output from the sensor unit 10, the changeover switches 36, 37, 38, 39 of the signal processing circuit 33 are switched to the e side by a control circuit (not shown) or the like. By this switching, the sensor unit 10
Current of about 1 mA from the constant current source 34 to the extent that the resistance value of the resistor part 11 of FIG.
Flow to 1. Then, the voltage corresponding to the resistance value of the contact resistance part 12 of the sensor part 10 is detected, and the resistance value of the contact resistance part 12 is measured by this voltage value.

According to this comparative example, since the constant current source 34, the four changeover switches 36, etc. are required, an increase in the circuit scale cannot be avoided. However, according to the first embodiment, no constant current source is required, and three resistors and changeover switch 1 are used.
Since it is possible to configure the circuit in one, it is possible to reduce the number of parts and further downsize the circuit. According to the first embodiment, the output voltage of the sensor unit 10 is corrected based on the measured resistance value of the contact resistance unit 12 of the sensor unit 10.
It has the effect of extending the life of 0.

Further, according to the first embodiment, since the circuit of the signal processing circuit 20 can be constituted by the three resistors 21 and the like and the one changeover switch 25, the circuit can be simply constructed. Further, according to the first embodiment, since the number of parts of the circuit of the signal processing circuit 20 is small, there is an effect that the failure occurrence rate can be lowered and the cost can be reduced.

In the first embodiment, the rotary sliding resistor is used for the sensor unit 10. However, the present invention is not limited to this as long as it is a sliding resistor, and for example, a linear resistor A sliding type sliding resistor may be used. In the first embodiment, A
The / D converter 30 used has a resolution of 16 bits, but in the present invention, the resolution is not limited to this as long as an analog signal can be converted into a digital signal. For example, the resolution is 18 bits or 20 bits. Further, an A / D converter having a resolution higher than this may be used, and an A / D converter having a low resolution of, for example, 14 bits or 12 bits may be used.
A D converter may be used.

(Second Embodiment) A second embodiment in which the position sensor signal processing circuit of the present invention is applied to a position sensor signal processing system.
An example is shown in FIGS. 7 and 8. In FIG. 7, the same components as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals. The second embodiment does not have a protective resistor for the operational amplifier 24 because the changeover switch 27 of the signal processing circuit 40 is not provided with a midpoint as shown in FIG. 7, and as shown in FIG. The difference from the first embodiment is that the sensor output voltage is constantly corrected by switching the switch 27.

As shown in FIG. 7, the signal processing circuit 40 includes
Resistors 21, 22, operational amplifier 24, changeover switch 27
It consists of The resistors 21 and 22 function as pull-up resistors and pull-down resistors, respectively, as in the first embodiment. Since the changeover switch 27 is a two-contact switch and does not have a middle point, it does not have a protection resistor for the operational amplifier 24. This is because the changeover switch 27 does not switch to the a side or the b side and becomes neutral, and the non-inverting input terminal of the operational amplifier 24 is always connected to the resistor 21 or the resistor 22. Further, in the second embodiment, the position sensor signal processing system always operates as will be described later. Therefore, when the sensor unit 10 is disconnected, this disconnection is immediately detected and the non-inverting input terminal of the operational amplifier 24 is not opened. Can be controlled as follows.

The operation of the position sensor signal processing system will be described with reference to the flow chart shown in FIG. In step 81, the changeover switch 27 of the signal processing circuit 40 is changed over to the "a" side, the terminal V1 is connected to the resistor 21, and the sensor output voltage is pulled up. The output voltage V4 at this time is measured through the A / D converter 30 in step 82 and set to Vp. Next, at step 83, the changeover switch 27 of the signal processing circuit 40 is changed over to the b side, the terminal V1 is connected to the resistor 22 and the sensor output voltage is pulled down. The output voltage V4 at this time is set to A in step 84 as in step 82.
Measured through the / D converter 30 and set to Vd. Step 8
2 and Vp and Vd measured by step 84,
Actual resistance value R of the resistors 21 and 22, actual power supply voltage V
Substituting cc into the equation (3) described in the first embodiment, step 8
The resistance value Rc of the contact resistance portion 12 is calculated from 5. Further, in step 86, this Vd, the contact resistance part 1
The resistance value Rc of 2 and the actual resistance value R of the resistor 22 are substituted into the equation (5) described in the first embodiment to calculate the corrected sensor output voltage Vx. After the completion of the calculation in step 86, the process returns to step 81 and the calculation processes in steps 81 to 86 are repeated. This repetition cycle differs depending on the rotation or movement speed of the position sensor of the device using the position sensor signal processing system, and is, for example, about 0.5 seconds when used for a throttle position sensor of an automobile. However, the arithmetic unit 31, which is capable of high-speed arithmetic processing,
A / D converter capable of high-speed conversion processing to the / D converter 30,
By using a high-speed semiconductor switch or the like as the changeover switch 27, the repetition cycle can be made extremely small in the present invention.

According to the second embodiment, since the output voltage of the sensor section 10 is constantly corrected, there is an effect that it can be detected immediately after the occurrence of a failure of the sensor section 10. Further, according to the second embodiment, the circuit of the signal processing circuit 40 can be configured by the two resistors 21 and the like and the one changeover switch 27, so that there is an effect that the circuit can be configured more simply than in the first embodiment. is there.

Further, according to the second embodiment, since the number of circuit components of the signal processing circuit 40 is small, there is an effect that the failure occurrence rate can be further lowered and the cost can be reduced as compared with the first embodiment. The signal processing circuit of the position sensor of the present invention described above is not limited to this embodiment, and may be, for example, an accelerator pedal, a throttle valve, an accelerator lever of a distribution type fuel injection pump, a control rack of a row type fuel injection pump. It is used for position sensors.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a sensor unit and a signal processing circuit of a position sensor signal processing system according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a position sensor signal processing system according to a first embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram when the changeover switches of the signal processing circuit of the position sensor signal processing system according to the first embodiment of the present invention are changed over to a side and b side respectively.

FIG. 4 is a characteristic diagram of the sensor output voltage with respect to the rotor rotation angle of the sensor of the position sensor signal processing system according to the first embodiment of the present invention.

FIG. 5 is a flow chart diagram of arithmetic processing and the like of the position sensor signal processing system according to the first embodiment of the present invention.

FIG. 6 is an equivalent circuit diagram of a sensor unit and a signal processing circuit according to a comparative example.

FIG. 7 is an equivalent circuit diagram of a sensor unit and a signal processing circuit of a position sensor signal processing system according to a second embodiment of the present invention.

FIG. 8 is a flowchart diagram of arithmetic processing and the like of the position sensor signal processing system according to the second embodiment of the present invention.

[Explanation of symbols]

 10 sensor part 11 resistor part (resistor) 12 contact resistor part (contact resistance) 20 signal processing circuit 21 resistor (first resistor) 22 resistor (second resistor) 23 resistor 25 changeover switch (Contact switching means) 30 A / D converter (signal converter) 31 arithmetic unit (control means, arithmetic means)

Claims (6)

[Claims] 1. A resistor in which a voltage is applied to one electrode and the other electrode is connected to a reference potential, and a voltage which slides on the resistor and is correlated to a sliding position is based on the reference potential. A contact portion having an output terminal for outputting, a contact switching means having a common terminal connected to the output terminal, the common terminal being connected to one of the contacts, one contact of the contact switching means, and the contact A first resistor connected between the electrode at one end of the resistor, and a second resistor connected between the other contact of the contact switching means and the electrode at the other end of the resistor. And a control means for switching the contact switching means to one of the contacts according to an output voltage output from the output terminal and applying the output voltage to the first resistor or the second resistor. Position sensor signal processing characterized by Circuit. 2. A signal processing circuit for a position sensor according to claim 1, wherein the contact switching means is provided on a circuit side including the first resistor and the second resistor. 3. The controller contacts the resistor with the voltage Vp applied to the first resistor by the controller and the voltage Vd applied to the second resistor by the controller. The signal processing circuit of the position sensor according to claim 1, further comprising a calculation unit that calculates a resistance value of a contact resistance generated between the position sensor and the section. 4. The signal processing circuit of the position sensor according to claim 3, wherein the calculating means calculates the resistance value of the contact resistance from a potential difference between the voltage Vp and the voltage Vd. 5. The calculation means corrects the output voltage from the resistance value of the contact resistance.
Alternatively, the signal processing circuit of the position sensor according to item 4. 6. The arithmetic means comprises a signal converter for converting an output voltage output from the output terminal into a digital signal, and an arithmetic unit for arithmetically processing the digital signal output from the signal converter. The signal processing circuit for the position sensor according to claim 3, 4, or 5.