Digital angle detection system

Abstract: The present invention relates to a digital angle detection system, or more particularly, to provide a digital angle output that is stable and the least affected by a cable length or the like. A digital angle detection system of the present invention uses a phase signal [ sin(ω t-90° -  ) ] produced by synthesizing a phase-shifted resolver signal cos · sin(ω t- 90°) , which is 90° out of phase with one resolver signal cos · sinω t , with the other resolver signal sin · sinω t .

Description: BACKGROUND OF THE INVENTION The present invention relates to a digital angle detection system using a resolver as a sensor. More particularly, this invention is concerned with a novel improvement for providing a digital angle output that is stable and less affected by cable length or the like. In general, conventional digital angle detection systems fall into tracking types and phase types. A typical example of a phase type system has the configuration shown in Fig. 1. A single-phase resolver signal sin(ω t-), which is provided by a resolver 2 that is a rotor detector and that receives two excitation signals of different phases sinω t and cosω t from a two-phase exciter 1, is fed to a phase comparator 4 via a waveform shaper 3. An output signal 4a of the phase comparator 4 passes through a loop filter 5, a variable frequency generator 6, and an output counter 7. A digital angle output  (where  equals ) ensues. A subtracter 8 linked to the output counter 7 is connected to a ring counter 9 that is linked to the two-phase exciter 1. Because of the foregoing configuration, the conventional digital angle detection system has problems described below. To be more specific, a resolver that receives two excitation signals of different phases and outputs one single-phase voltage is used to detect an angle as a phase difference of a resolver signal and transfer the angle information. The precision of the angle information is dependent greatly on an impedance of a signal transmission line, which is determined by a cable length from the resolver to a signal processor, or by a temperature change. It is very hard to provide a high-precision digital angle output. Moreover, a two-phase exciter is indispensable. This leads to complex circuitry and high cost. United States Patent 4,096,476 discloses a circuit for reading an inductosyn having first and second signal outputs which are then combined to provide a phase-modulated wave. This wave is then squared and pulse-counted to determine a phase difference. However, there is no correction for the impedance of the signal transmission line from the inductosyn. The present invention attempts to solve the above problems. An object of the present invention is to provide a digital angle detection system in which a resolver that receives one single-phase excitation signal and outputs two signals of different phases is used in the same manner as it is used in a tracking type system, so that a digital angle output, which is stable and less affected by a cable length or a temperature change, can be provided. According to the present invention, there is provided a digital angle detection system for providing a digital angle output () in response to first and second resolver signals (sin  • sin ωt, cos  • sin ωt) received from a resolver (2), comprising: a phase shifter for phase shifting the said second resolver signal; an adder/subtracter (22) for receiving the said first resolver signal (sin  • sin ωt) and a phase-shifted resolver signal (cos  • sin (ωt - 90°)) output from the said phase shifter (31) and formed by the said phase shifter (31) phase-shifting the said second resolver signal (cos  • sin ωt) by 90°; a latch circuit (24) for receiving a phase signal defining a sample signal (sin (ωt-90° - )) from said adder/subtracter (22) via a wave forming circuit (23); a phase splitter/selector 20 for receiving said first and second resolver signals [(sin  • sin ωt), (cos  • sin ωt)] and splitting them into four phase signals which differ from each other in phase by 90°; a phase counter (21) which is connected with the output of the said phase splitter/selector (20) for generating a phase counting signal (21a) for supply to the said latch circuit (24); a reference signal generator (35) for generating a reference signal (sin ωt) to act as a reference and an excitation source for phase splitting and selection undertaken by the said phase splitter/selector (20); and an oscillator (9) for supplying a clock signal (9a) to the said phase counter (21) and the reference signal generator (35); whereby, in use the phase correction signal (20a) serving as a reference signal for the said phase counter (21) is generated, said reference signal being used for pre-setting said phase counter (21), said phase counting signal (21a) being latched in said latch circuit (24) by said phase signal (sin (ωt - 90°)) and converted into a digital angle output (). Preferred features of the invention are set out in claims 2 to 4. Fig. 1 shows a block diagram showing a conventional system. Fig. 2 is a block diagram showing a digital angle detection system of the present invention; Fig. 3 shows waveforms describing digital conversion, and phase split and selection; Referring to the drawings, a preferred embodiment of a digital angle detection system of the present invention will be described in detail below. Components identical to those in the conventional system will be assigned the same reference numerals. In Fig. 2, reference numeral 2 denotes a known resolver that receives one single-phase excitation signal and outputs two signals of different phases. A first resolver signal sin • sinω t and a second resolver signal cos • sinω t, which are provided by the resolver 2, are fed to a phase splitter/selector 20. The phase splitter/selector 20 splits the resolver signals sin • sinω t and cos • sinω t into four signals, which differ from each other in phases of 90° and represent constituent parts of a rotor angle , according to the amplitudes of the resolver signals (See Fig. 3), and then outputs a phase correction signal 20a as a reference signal for a phase counter 21. The first resolver signal sin · sinω t and a phase-shifted resolver signal cos · sin(ω t-90°), which is produced by a 90° phase shifter 31 so that it will be 90° out of phase with the second resolver signal cos • sinω t are synthesized by an adder/subtracter 22. A resultant synthetic resolver signal used as a phase signal sin(ω t-90°-) is reshaped by a waveform shaper 23 and then fed as a sampling pulse shown in Fig. 3 to a latch 24. The phase correction signal 20a is fed to the phase counter 21. With the phase correction signal 20a, a reference value is preset in the phase counter 21. A phase counter signal 21a provided by the phase counter 21 is latched by the latch 24 responsively to the phase signal sin(ω t-90°-) that is the synthetic resolver signal and serves as a sampling pulse. The latch 24 provides a digital angle output. While being stored in an output buffer 40, the digital angle output has the output form thereof adjusted and is supplied as a digital angle output . The phase counter 21 receives a clock signal 9a produced by an oscillator 9. The clock signal 9a is also fed to a generator 35 for generating a reference signal sinω t. The generator 35 feeds the excitation signal sin ωt to each of a current control amplifier 50 and the phase splitter/selector 20. The excitation signal sin ωt thus works as a reference signal for phase split and selection. The signals REF. R1, 2, 3 and 4 are generated by the generator 35 for generating phase selection signal phase , 1, 2 and 3 from a phase splitter/selector 20. Next, the operation will be described. First, the resolver signals sin  • sin ωt and cos  • sin ωt are, as shown in Fig. 3, subjected to phase split. The phase split brings about four signals that differ from one another in phases of 90° and represent constituent parts of a rotor angle  of the resolver 2. That is to say, the phase splitter/selector 20 uses the amplitudes of the resolver signals sin . sinω t and cos • sinω t having the waveforms shown in Fig. 3 to produce phase selection signals PHASE  to PHASE 3. Thus, a signal representing the cosine of the rotor angle that is within ±45° is supplied repeatedly. The range of ±45° is determined because the amplitude of the signal representing the cosine of the rotor angle does not vary drastically and therefore the phase correction signal 20a serving as a reference signal for the phase counter 21 can be produced easily. The second resolver signal cos • sinω t is subjected to 90° phase shift by the 90° phase shifter 31. This results in a signal cos • sin(ω t-90°) ··· (1). On the other hand, the first resolver signal sin • sinω t is synthesized with the signal cos • sin(ω t-90°) ... (1) by performing known addition expressed below. cos • sin(ω t-90°) - sin • sinω t = -cos • cosω t - sin • sinω t = -cos(ω t-) = sin(ω t-90°- ) The expression (2) means that an angle  is regarded as a phase shift of a sine wave. The expression (2) can be implemented in a converter means in a conventional phase type system. However, when the expression (2) is used, it must be taken into consideration that a 90° offset is automatically specified. The angle  is confined to values within ±45°. The signal of said formula (1) therefore has, as shown in Fig. 3, an amplitude that is larger than a certain level. This is preferred for producing the phase correction signal 20a. The phase correction signal 20a serves as a preset signal PC-PRESET (See Fig. 3) for the phase counter 21. Specifically, with the phase correction signal 20a, a phase that leads 90° is preset in the phase counter 21 so that the 90° offset will be canceled out. The phase correction signal 20a also serves as a reference signal. Digital angle detection is based on the conventional phase technique using the waves shown in Fig. 3. After the phase counter 21 is preset with the preset signal PC-PRESET, each of counter outputs PC1 to PC12 (PC9 to PC12 alone are shown in Fig. 3) is latched responsively to the phase signal sin (ω t-90°-) by means of the latch 24, then converted into angle information. It is easy to cancel out the 90° offset, because the reference signal sinω t is produced using the resolver signals sin · sinω t and cos ·sinω t. Phase errors of the resolver signals, which are attributable to a transmission line or a cable linking the resolver 2 and the circuitry or to a temperature change, can be corrected automatically. The aforesaid embodiment includes the phase counter 21 and latch 24. Alternatively, a CPU may be used to run software having the capabilities of these circuit elements. What is used as a sensor is not limited to the resolver 2 that receives one single-phase excitation signal and outputs two signals of different phases. A general synchro device may be used in conjunction with transformers that are interconnected according to Scott connection. This variant will provide the same resolver signals as those mentioned above. This embodiment can apply to any sensor as long as the sensor can output sine waves that are mutually 90° out of phase. The application of the system of this embodiment is not limited to angle detection but may be the usage as a means for converting two sine waves of different phases into digital forms. A digital angle detection system of the present invention has the aforesaid configuration and therefore has the following advantages: the simplified circuitry (constructed as a one-chip LSI) realizes a low price and high reliability. Moreover, the system of the present invention permits higher precision than the conventional phase type system, and enables faster processing than the conventional tracking type system. Furthermore, a resolver that inputs one single-phase excitation signal and outputs two signals of different phases is used and a reference signal is produced using the resolver signals. The phase errors of the resolver signals attributable to a transmission line or a cable linking the resolver and circuitry or to a temperature change can be corrected automatically. Consequently, a digital angle output that is stable and the least affected by a cable length or by a temperature change can be provided.

Claims: A digital angle detection system for providing a digital angle output () in response to first and second resolver signals, sin  • sin ωt, cos  • sin ωt, received from a resolver (2), comprising: a phase shifter for phase shifting the said second resolver signal; an adder/subtracter (22) for receiving the said first resolver signal, sin  • sin ωt, and a phase-shifted resolver signal, cos  • sin (ωt - 90°), output from the said phase shifter (31) and formed by the said phase shifter (31) phase-shifting the said second resolver signal, cos  • sin ωt, by 90°; a latch circuit (24) for receiving a phase signal defining a sample signal, sin (ωt-90° - ), from said adder/subtracter (22) via a wave forming circuit (23); a phase splitter/selector 20 for receiving said first and second resolver signals, sin  • sin ωt, cos  • sin ωt, and splitting them into four phase signals which differ from each other in phase by 90°; a phase counter (21) which is connected with the output of the said phase splitter/selector (20) for generating a phase counting signal (21a) for supply to the said latch circuit (24); a reference signal generator (35) for generating a reference signal sin ωt to act as a reference and an excitation source for phase splitting and selection undertaken by the said phase splitter/selector (20); and an oscillator (9) for supplying a clock signal (9a) to the said phase counter (21) and the reference signal generator (35); whereby, in use, a phase correction signal (20a) serving as a reference signal for the said phase counter (21) is generated, said latter reference signal being used for pre-setting said phase counter (21), said phase counting signal (21a) being latched in said latch circuit (24) by said phase signal, sin (ωt - 90°-), and converted into a digital angle output (). A digital angle detection system as claimed in claim 1, wherein the phase splitter/selector is responsive to the amplitudes of the resolver signals. A digital angle detection system as claimed in claim 1 or claim 2, wherein the reference signal generator provides a single phase excitation signal to the resolver. A digital angle detection system as claimed in any one of claims I to 3, wherein the reference signal generator provides an excitation signal in response to an internal reference clock.

Inventors: KUSHIHARA HIROSHI, KUSHIHARA, HIROSHI, Kushihara, Hiroshi, c/o Tamagawa Seiki K.K.
Applicants: TAMAGAWA SEIKI CO LTD, TAMAGAWA SEIKI KABUSHIKI KAISHA
Application year: 1995
Main classification: H03M1
IPC codes: G01D5, G06G7, G01B7, H03M1