Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Reexamination Certificate
2001-11-06
2003-02-18
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
C318S661000, C324S207110, C324S207130
Reexamination Certificate
active
06522097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position detecting apparatus and an abnormality detecting apparatus, and more particularly to a resolver for detecting a position or a device for detecting the rotational position such as a synchro, and most particularly to a position detecting apparatus and an abnormality detecting apparatus for detecting the position of a motor for driving a brushless motor.
2. Description of the Related Art
FIG. 7
shows a conventional position detecting apparatus of this type as disclosed in, for example, Japanese Patent Laid-open No. 9-126809. Referring to
FIG. 7
, for example, a position sensor
10
made up of a resolver is inputted with an excitation signal (sin &ohgr;t) which is a sine wave voltage for excitation from an oscillating circuit
22
that generates the excitation signal on the basis of a clock of a counter
12
. The position sensor
10
outputs induction signals sin &thgr; sin(&ohgr;t±&agr;) and cos &thgr; sin(&ohgr;t±&agr;) resulting from amplitude-modulating the excitation signal cos &thgr; and sin &thgr; in response to the rotational position &thgr;. Here, &agr; represents a phase fluctuation error of the output signal to the excitation signal due to a path of from the position sensor
10
to a position detecting circuit or a change in the temperature of a position sensor winding.
One output signal sin &thgr; sin(&ohgr;t±&agr;) has its phase shifted by a phase shifting circuit
14
by a given value of 90 degrees, so the output signal becomes a phase shift output sin &thgr; cos(&ohgr;t±&agr;). The phase shift signal and another output signal cos &thgr; sin(&ohgr;t±&agr;) from the position sensor
10
are added together by an adding circuit to output an addition signal sin(&ohgr;t+&thgr;±&agr;). Similarly, the phase shift signal and another output signal cos &thgr; sin(&ohgr;t±&agr;) outputted from the position sensor
10
are subtracted from each other by a subtracting circuit to output a subtraction signal sin(&ohgr;t−&thgr;±&agr;).
The excitation signal (sin&ohgr;t) which is a reference signal is counted with reference to a counter
12
. That is, since the excitation signal is counted as one period of from 0 to 360 degrees, a zero-cross point of the addition signal sin(&ohgr;t+&thgr;±&agr;) is detected by a zero-cross detecting circuit
17
, and data D
1
latched by a latch circuit
19
becomes +&thgr;±&agr;. Similarly, the zero-cross point of the subtraction signal sin(&ohgr;t−&thgr;±&agr;) is detected by the zero-cross detecting circuit
18
, and data D
2
latched by the latch circuit
20
becomes −&thgr;±&agr;. In addition, in an error calculating circuit
21
, (D
1
+D
2
)/2 becomes ±&agr; as described above. Therefore, the phase fluctuation error ±&agr; can be calculated. The data D
1
and the phase fluctuation error ±&agr; are subtracted from each other by the subtracting circuit
22
, thereby being capable of obtaining &thgr;, and also capable of extracting the position &thgr; from which the phase fluctuation error ±&agr; is removed.
Because the conventional position detecting apparatus disclosed in Japanese Patent Laid-Open No. 9-126809 is structured as described above, when the position detecting apparatus fails due to some cause, in particular when the phase shifting circuit
14
fails and the phase shift is not effected, the addition signal becomes sin &thgr; sin(&ohgr;t±&agr;)+ cos &thgr; sin(&ohgr;t±&agr;)=(sin &thgr;+cos &thgr;)sin(&ohgr;t±&agr;), and the subtraction signal becomes sin &thgr; sin(&ohgr;t±&agr;)−cos &thgr; sin(&ohgr;t±&agr;)=(sin &thgr;−cos &thgr;)sin(&ohgr;t±&agr;). Therefore, the data D
1
becomes ±&agr; or 180 degrees ±&agr; except that &thgr; is 135 degrees or 315 degrees, and also the data D
2
becomes ±&agr; or 180 degrees ±&agr; except that &thgr; is 45 degrees or 225 degrees. Therefore, &thgr; detects any one of ±&agr;, 90 degrees ±&agr;, 180 degrees ±&agr;, and 270 degrees ±&agr;. For simple description, if &agr; is 0, a relationship between the original position (for example, motor rotation position) and the detected position is shown in FIG.
8
. The error becomes 135 degrees at the maximum, and in the case where the apparatus is used as a motor rotation position detecting apparatus for driving a brushless synchronous machine, there is the possibility that malfunction occurs such that the apparatus drives the synchronous machine in a direction opposite to a normal drive direction. In order to prevent this drawback, there has been proposed that two position detecting apparatuses are disposed, and two detection results are compared with each other to judge whether a failure occurs, or not. In this proposal, since two position detecting apparatuses are required, it becomes expensive.
Also, in order to calculate the position &thgr;, because the phase fluctuation error ±&agr; is calculated once, and then calculation processing except for the position fluctuation error is required, the structural circuit becomes complicated and expensive.
SUMMARY OF THE INVENTION
The present invention has been made under the above circumstances, and therefore an object of the present invention is to provide a position detecting apparatus and an abnormality detecting apparatus which are capable of minimizing an influence of a failure even if a phase shifting circuit fails.
With the above objects in view, the position detecting apparatus comprises: a position sensor that inputs an excitation signal having a given period waveform and outputs a first amplitude modified signal induced in accordance with a detected position from a first output winding and outputs a second amplitude modified signal induced in accordance with a detected position from a second output winding; a first phase shifting means for electrically shifting a phase of the first amplitude modified signal by a given angle; a second phase shifting means for electrically shifting a phase of the second amplitude modified signal by a given angle; a converting means for converting the signal outputted from the first phase shifting means and the signal outputted from the second phase shifting means into a phase modulated signal; and a calculating means for obtaining a detected position on the basis of the phase of the phase modulated signal outputted from the converting means.
The calculating means may detect a phase difference between the excitation signal and the phase modulated signal to obtain the detected position.
REFERENCES:
patent: 4034483 (1977-07-01), Bernstein et al.
patent: 5072173 (1991-12-01), Halder et al.
patent: 5189353 (1993-02-01), Ezuka
patent: 5260650 (1993-11-01), Schwesig et al.
patent: 5332955 (1994-07-01), Hopper
patent: 5347277 (1994-09-01), Nondahl et al.
patent: 5710509 (1998-01-01), Goto et al.
patent: 6239571 (2001-05-01), Shimahara
patent: 9-126809 (1997-05-01), None
Fujimoto Chiaki
Kifuku Takayuki
Matsushita Masaki
Leykin Rita
Sughrue & Mion, PLLC
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