JPS61295852A - Rotating phase detector of dc motor - Google Patents

Abstract

PURPOSE:To enhance the detecting accuracy by providing a position detecting magnet on a rotor magnet, providing a magnetic resistance element not opposed to a magnetic resistance element opposed thereto to detect the output difference, thereby cancelling the influences of environmental magnetic flux and the temperature. CONSTITUTION:A position detecting magnet 3 is mounted to detect the position of a rotor on a magnet case 8 of a rotor magnet 7. Two magnetic resistance elements 1, 2 are prepared at a stator side, one is disposed at a position for receiving the magnetic flux of the magnet 3, and the other is disposed at the position not receiving the flux and at the position where both are disposed in the same environment. The difference of the outputs of the two elements 1, 2 is obtained as a position detection signal. Thus, the effects of the leakage magnetic flux of the rotor magnet 7 and the environmental temperature are cancelled to obtain an accurate position detecting signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for detecting position detection signals (
This invention relates to a rotational phase detection device for a DC motor that detects a position detection magnet (hereinafter referred to as a PG multiplied signal) using a magnetoresistive element (hereinafter referred to as an MR element) attached to a part of a rotating body.

BACKGROUND ART In general, as a PG signal detection device using an MR element, a position detection magnet 3 is arranged on a rotor magnet 7 of a motor as shown in FIGS. 2a and 2b due to space constraints. An MR element 6 is placed at the position where the magnet 3 is detected.
is arranged, and the MR element 6 is arranged in a circuit represented by FIG. 2C.
The signal is extracted by converting the resistance change into a voltage change.

Problems that the invention aims to solve However, with conventional devices, due to space constraints, etc.
As shown in FIGS. a and b, the mounting position of the position detection magnet 3 often occurs above the rotor magnet 7. In this case, in order to prevent leakage of magnetic flux from the rotor magnet 7 to the outside, its sides are covered with a magnet case 8 made of magnetic material, but in order to completely prevent leakage of magnetic flux, two or three layers are covered. Magnetic shielding measures are required, which increases costs. For this reason, as shown in FIG. 2, there are many structures that include only a heavy magnet case 8.

In this case, since there is magnetic flux leakage from the magnet case 8 to the rotor magnet 7, the output of the MR element 6 is
In addition to the PG signal, a noise N corresponding to the number of magnetized poles of the rotor magnet 7 is added. For this reason, in the past, the PG signal output was made as large as possible to ensure a large difference from the noise N, and the detection point was placed at a potential above the noise level, but the output of the MR element has an upper limit, and if cannot be made larger. On the other hand, since the resistance and sensitivity of MR elements change depending on the operating temperature, the noise level increases or decreases depending on the temperature.For this reason, it is necessary to keep the noise level below a certain level when the operating temperature range is wide. There was a problem in that magnetic shielding measures had to be taken for the magnet case.

The present invention solves these conventional problems and provides a PG multiplied signal that is not particularly affected by temperature.

Means for Solving the Problems The rotational phase detection device of the present invention has two MR elements with the same characteristics at positions that simultaneously detect the magnetic poles of the same polarity of the rotor magnet, and one of which is located at the position of the magnet for position detection. In addition, the other is installed at the non-detection position of the position detection magnet, and the differential output of both MR elements is extracted as a PG multiplied signal. 〇Function According to the above configuration, noise due to leakage magnetic flux from the rotor magnet is The components are canceled by taking the difference between the outputs of both MR elements, and it is also possible to prevent noise output changes due to temperature changes. Further, with this configuration, it is possible to cancel the influence of peripheral magnetic flux other than the position detection magnet 3, and it is possible to obtain a stable PG multiplied signal that is not affected by external influences.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention, and the same components as those of the conventional example shown in FIG. 2 are given the same reference numerals.

As shown in FIGS. 1a and 1b, one of the two MR elements 1 and 2 with the same characteristics is placed at the detection position of the position detection magnet 3, and the other MR element 2 is placed at the position of the MR element 1. MR elements 1 and 2 are installed in the non-detection position of the position detection magnet 3, which has been moved in the direction of the rotational axis of the rotor, and these two MR elements 1 and 2 are wired in series between a constant voltage power source and ground as shown in Figure 1C. . Note that the MR element 2 may be located at any other location within the range of the non-detection position of the position detection magnet 3 as long as the leakage magnetic flux from the same magnetic pole of the rotor magnet is at the same level as the MR element 1 as much as possible. According to this configuration, the resistance changes of the MR elements 1 and 2 due to the leakage magnetic flux of the rotor magnet 7 are the same, and the difference output between the two MR elements 1.2 is determined by the rotor magnet 7.
There is no voltage change due to (, a voltage change occurs only when MR element 1 detects a PG multiplied signal. Also, resistance changes due to temperature and the influence of external magnetic flux occur simultaneously on both MR elements, so they must cancel each other out.) This makes it possible to obtain a stable PG multiplied signal.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a PG multiplied signal indicating the rotational phase of the rotor magnet from which the influence of the magnetic flux of the rotor magnet has been removed by using a simple configuration, and it is also possible to obtain a PG multiplied signal indicating the rotational phase of the rotor magnet, which is free from the influence of the magnetic flux of the rotor magnet. The PG multiplication signal fluctuation due to the change is also reduced.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main parts of a rotational phase detection device for a DC motor according to an embodiment of the present invention, Fig. 1 is a side view of the main parts, and Fig. 1C is an electrical connection of the main parts. Figure 2 & is a perspective view of the main parts of a conventional DC motor rotational phase detection device.
The figure is a side view of the same main part, FIG. 2C is an electrical connection diagram of the same main part, and FIG. 2D is an operating waveform diagram of the same device. 1.2... Magnetoresistive element, 3... Magnet for position detection, 7... Rotor magnet, 8... Magnet case〇Name of agent Patent attorney Toshio Nakao and 1 other person f,
? ,,, ＋Quantitative talent 8 72°net case figure 2

Claims (1)

[Claims] A position detection magnet is provided on the rotor magnet of the DC motor, one of the two magnetic resistance elements is placed at a position where the magnetic flux of the position detection magnet is detected, and the other is placed at a position where the magnetic flux of the position detection magnet is influenced. and a position where both magnetic resistance elements equally receive the magnetic flux of the same polarity of the rotor magnet, and the difference component between the outputs of the two magnetic resistance elements is detected as a rotational phase signal of the rotor magnet. A rotational phase detection device for a DC motor configured as follows.