JPH0342790B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a speed detection device for detecting the moving speed of a moving object, and particularly to a speed detection device for detecting the rotation speed of a spindle motor used in a machine tool to rotationally drive a cutting tool. The present invention relates to a speed detection device suitable for speed detection.

[Conventional technology]

FIG. 2 shows an example of this type of speed detection device, in which a gear 12 is fixed to a motor shaft 11 of a motor whose rotational speed is detected.
A permanent magnet 5 and a magnetic sensor element group 2 whose magnetic resistance changes depending on the amount of magnetic flux from the permanent magnet 5 are arranged facing each other at a predetermined interval from the permanent magnet 2 .

The magnetic sensor element group 2 includes four magnetic sensors 2.
1, 22, 23, 24, of which a set of two magnetic sensors 21, 22 each and 23, 2
4 sets are connected in series, a DC voltage V _cc (for example, 5V) is applied to both ends of each set, and voltages V ₁ and V ₂ at the midpoint of each set are applied to comparators 61 and 62, respectively. A reference voltage of V _cc /2 is applied to the other input sides of the comparators 61 and 62 . It should be noted that the sets of magnetic sensors 21 and 22 and the set of magnetic sensors 23 and 24 connected in series are one of each set, for example, 2
When 1 or 23 is facing the mountain of gear 12,
The other 22 or 24 is dimensioned to face the valley of the gear 12, and the set of magnetic sensors 21, 22 and the set of magnetic sensors 23, 24 are arranged offset by 1/4 of the pitch of the gear. ing.

These magnetic sensor elements 21, 22, 23, 2
4 has a characteristic that when the magnetic flux from the permanent magnet 5 passes through it, its magnetic resistance increases as the amount of the magnetic flux increases, and its material is, for example, indium antimony alloy or thin film permalloy.

In this way, if the peaks of the gear 12 face the magnetic sensor 21 and the valleys of the gear 12 face the magnetic sensor 22 due to the rotation of the motor, the amount of magnetic flux passing through the magnetic sensor 21 increases. As a result, the amount of magnetic flux passing through the magnetic sensor 22 decreases, decreasing its magnetic reluctance and resulting in a decrease in the midpoint voltage V ₁ . Conversely, the gear 12
If the troughs of the gear 12 face the magnetic sensor 21, and the peaks of the gear 12 face the magnetic sensor 22, the voltage _V1 at the midpoint increases. As a result, the voltage at the midpoint
V ₁ varies sinusoidally around V _cc /2 as shown in FIG. 3 in accordance with the rotation of the motor, that is, the rotation of the gear. In this way, by supplying the voltage V ₁ that changes sinusoidally around V _cc /2 to one input side of the comparator 61, and applying the reference voltage of V _cc /2 to the other input side, Therefore, the comparator 6
A digital signal V _A that alternately repeats 0 and 1 is output from the output side of 1, and the rotational speed of the motor is detected based on the frequency of this signal.

Note that the midpoint voltage between the pair of magnetic sensors 21 and 22 and the pair of magnetic sensors 23 and 24, which are arranged 1/4 pitch apart from the gear 12 (a sine wave voltage centered at V _cc /2) V ₂ is 90° out of phase with the midpoint voltage V ₁ of the pair of magnetic sensors 21 and 22 (see FIG. 3), and the midpoint voltage V ₂ is supplied to one input side of the comparator 62. The digital signal V _B output to the output side is also shifted in phase by 90° from the digital signal V _A. And these two signals V _A , V _B
The rotational direction of the motor can also be determined based on the phase relationship between the two.

Compared to other speed detecting devices such as pulse encoders or DC motors (tachometer generators), the speed detecting device with this configuration has a smaller number of components and is simpler in structure, and is therefore reliable despite its low cost. It has advantages such as high performance.

[Problem that the invention seeks to solve]

However, when the motor is used at high speed or under heavy load, the temperature of the motor increases. In such a case, due to variations in the temperature characteristics of each magnetic sensor element, the midpoint voltage of each set of magnetic sensor elements (ideally, this midpoint voltage is
V _cc /2 (so that the comparison operation of the comparator can be performed accurately) deviates from V _cc /2, and the change in the so-called output offset cannot be ignored, thereby causing There was a risk that the comparator would malfunction.

To solve this problem, the conventional method has been to select magnetic sensor elements that have uniform temperature characteristics, but this method has the problem that it is not suitable for mass production.

In addition, a capacitor is inserted into the circuit from the midpoint of each pair of magnetic sensor elements to the input side of each comparator to cut off the DC component of the midpoint voltages V ₁ and V ₂ to reduce the effect of changes in output offset. It is also possible to eliminate the capacitor, but with this method, when the motor rotates at a low rotational speed close to a stopped state (i.e., when the frequency of change in the midpoint voltage becomes extremely low), the capacitor The increased impedance makes it impossible to accurately detect the frequency change and therefore makes it impossible to detect all rotational speeds at which the motor starts from a standstill.

The present invention was made to solve this problem, and focuses on the fact that no matter where the gear is located, if the magnetic flux supplied to the magnetic sensor element is zero, the offset of the magnetic sensor element itself can be measured. However, an electromagnet is used instead of a conventional permanent magnet as an element that can control the amount of magnetic flux, and the motor is used immediately before it rotates (i.e., when the motor is stopped and there is no need to detect the speed).
Detect the midpoint voltage in the state of zero magnetic flux (as mentioned above, this voltage changes depending on the temperature state of the motor at that time and corresponds to the offset voltage mentioned above), and based on this detected voltage, Based on the idea of setting the reference voltage level of the comparator, the offset change of the magnetic sensor element is compensated to obtain an output signal that is not affected by the offset change.

Note that the speed detection device according to the present invention is suitable for speed detection of motors that operate and stop frequently (one operation time is relatively short), such as a spindle motor (motor for driving a cutting tool) in a machine tool. It is especially suitable when

In other words, if the offset voltage of this type of motor is detected as described above each time the motor stops, and the reference voltage level of the comparator is set based on the detected voltage at that time, the voltage level will be the same until the next stop. The temperature state of the motor does not change significantly during the motor operation, and the comparison operation of the comparator can be performed normally during operation of the motor by using the reference voltage level.

[Means for solving problems]

As a means for solving the above problems, the present invention includes an electromagnet, a magnetic sensor element whose magnetic resistance changes depending on the amount of magnetic flux generated by the electromagnet, and a comparator, and one input of the comparator. The midpoint voltage of the magnetic sensor element when the electromagnet is de-energized when the moving body is stopped is applied as a reference voltage to the other input side of the comparator. A position detection device for a moving object is provided that supplies a midpoint voltage of the magnetic sensor element that corresponds to a velocity.

[Effect]

According to the above configuration, one input side of the comparator is provided with a signal that is determined when the electromagnet is de-energized (i.e., unrelated to the position of the gear) when the moving body is stopped (i.e., when there is no need for speed detection). The midpoint voltage of the magnetic sensor element (which varies depending on the temperature state of the motor at that time) is set to be applied as the reference voltage of the comparator every time the moving body stops, and the other input side of the comparator is set to Offsetting changes in the offset of the magnetic sensor element due to the temperature change by supplying a midpoint voltage of the magnetic sensor element corresponding to the speed of movement of the moving object during an immediately subsequent movement period; Accurate speed detection can be performed by using an output signal that is not affected by such offset changes.

〔Example〕

FIG. 1 shows an embodiment of the speed detection device according to the present invention, in which the permanent magnet 5 in the conventional example is used as a device for supplying magnetic flux to the magnetic sensor element group 2.
An electromagnet 3 is used instead.

The motor drive circuit 4 is provided with a CPU 41,
The CPU 41 transmits a stop command to the motor 1 via the amplifier 49 to stop the motor 1, and then turns off the transistor 48, thereby de-energizing the electromagnet 3.

In this manner, during the period when the motor 1 is stopped, the electromagnet 3 is de-energized and the magnetic flux is zero, and during that time, the midpoint voltage of each pair of magnetic sensor elements 21, 22 and 23, 24 is applied to the A/D converter 43. , 46 perform A/D conversion and store the digital value in the CPU 41. Next, the stored digital values are D/A converted by D/A converters 44 and 47, and the analog values are converted to comparators 42 and 45, respectively.
is supplied as its reference voltage.

Note that this reference voltage setting operation is repeated until the motor 1 starts the next operation, and when the motor 1 starts the next operation, the reference voltage of the comparator is set according to the setting operation immediately before that operation. This reference voltage is then held at the set value during the next operation period.

When the next operation is started, the transistor 48 is turned on in response to a command from the CPU 41, the electromagnet 3 is excited, and the midpoint voltages V ₁ and V ₂ of the magnetic sensor elements corresponding to the rotational speed of the motor 1 are set. The output signals V _A and V _B are supplied to one input side of the comparators 42 and 45, and a predetermined comparison operation is performed based on the reference voltage. The speed of motor 1 is detected.

In this case, since the motor whose speed is detected by the speed detector of the present invention is operated for a relatively short time as described above, the temperature change of the motor during that time can be almost ignored. and the output signal V _A output from the comparator,
There is no error in _VB .

〔Effect of the invention〕

According to the present invention, offset changes in the magnetic sensor element due to changes in motor temperature can be eliminated, and accurate speed detection can be performed without being affected by such offset changes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a speed detection device as an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a conventional example of this type of speed detection device, and FIG. 3 is a diagram showing the configuration of a conventional speed detection device of this type. It is a figure showing the output voltage of the magnetic sensor element in . (Explanation of symbols), 1...Motor, 12...Gear,
2... Magnetic sensor element group, 3... Electromagnet, 4...
Motor drive circuit, 42, 45... comparator,
43, 46...A/D converter, 44, 47...
D/A converter, 48... Switching transistor, 49... Amplifier, 5... Permanent magnet, 61, 6
2...Comparator.

Claims (1)

[Claims] 1. An electromagnet 3, and magnetic sensor elements 21, 22 whose magnetic resistance changes according to the amount of magnetic flux generated by the electromagnet 3.
23, 24, and comparators 42, 45 that compare the midpoint voltage of the magnetic sensor elements 21, 22, 23, 24 with a reference voltage and output a signal corresponding to the movement of the moving object.
and a reference voltage output means 44 for outputting the reference voltage.
47, and a midpoint voltage measuring means 43 for measuring the midpoint voltage.
46, a switch means 48 for turning on/off the energization of the electromagnet 3, and a switch means 48 for turning on/off the energization of the electromagnet 3, each time the movable body stops.
After controlling the electromagnet to stop energizing the electromagnet and make it non-excited, the midpoint voltage is measured via the midpoint voltage measuring means 43 and 46, and the measured midpoint voltage is output as the reference voltage. A speed detecting device for a moving object, comprising: a control means 41 that automatically updates and outputs the reference voltage as the reference voltage via means 44 and 47.