Electricity: measuring and testing – Magnetic – Displacement
Patent
1991-04-16
1994-01-18
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Displacement
34087035, 32420725, 32420726, G01B 714
Patent
active
052802388
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a system for processing position signals such as stroke sensors, linear encoders, rotary encoders, etc.
BACKGROUND OF THE INVENTION
For example, for the detection of the stroke position of a piston rod of a hydraulic cylinder, it is customary to do a computation by converting into pulses the output signals from a magnetic sensor mounted on the cylinder side with a number of magnetic scales equally spaced embedded in the piston rod.
The magnetic sensor is intended to produce sinusoidal waves having one cycle per the minimum distance (one scale span) of the magnetic scale by the stroke of the piston rod, the output sinusoidal waves being set in a pair so as to be 90.degree. out of phase with respect to one another.
Detection of the stroke position of the piston rod is achieved by converting these outputs e.sub.A, e.sub.B from the sensor by the use of a comparator into square waves e.sub.A0, e.sub.B0, then inputting them into a phase discrimination or directional discrimination/multiply circuit, producing forward and backward pulses based on the following formulas, and counting these pulses by means of an up-and-down counter. ##EQU1## Where e.sub.A0 (.uparw.); pulses generated upon rise of e.sub.A0,
Thus, as for the resolution power of position detection, it is possible to detect a quarter of a cycle of the sensor output, i.e. up to the position of a quarter of a stroke of one scale span of the magnetic scale.
With such a system, however, one cycle only of the sensor output can be divided into four, and so improvement of the detection precision of stroke position requires an arrangement of the respective scale markings of the magnetic scale at short intervals. But, there is a processing limit in making fine magnetic scale marks on the surface of the piston rod, and this does not allow detection of very small strokes, accordingly.
The object of the present invention is to provide a system for processing position signals wherein a highly accurate detection of very small strokes can be made with the magnetic scale having marks at small intervals or pitches.
A further object of the present invention is to provide a system for processing position signals wherein the detection of position can be performed accurately and safely in any area of the output of the sensors.
SUMMARY OF THE INVENTION
In the present invention, there are provided a pair of sensors spaced in the direction of displacement in such a way as to produce sinusoidal signals corresponding to the positioning scale marks, means for pulse-width modulating these sensor outputs with the respective high-frequency sinusoidal waves as modulating signals, and means for converting the pulse-width modulated signals into position signals.
The output of the sinusoidal wave signals from the pair of sensors are pulse-width modulated based on high-frequency modulating signals, and each cycle of the sensor output signals is divided and interpolated in response to the frequency of the modulating signal in order to detect very small displacements.
In this instant, since the sinusoidal wave signals from the sensors are pulse-width modulated by modulating signals having the same sinusoidal waves, the duty ratio of the resulting pulse-width modulated signals will be in an approximate accord with values on straight lines interpolated in the sensor outputs, so that position signals thus detected will be linearized.
In the present invention, means are provided for dividing one cycle of the sensor output equally into a plurality of sections, means for selecting from among the divided sections a range that does not include the approximate regions of peak values of the sensor outputs, and means for converting into position signals the pulse-width modulated signals in the selected section.
Consequently, in this case, the non-use of the sensor outputs near the peak values may result in the avoidance of any influence of deviations (registration error) which may occur when the amplitudes and oscillation centers of the s
REFERENCES:
patent: 4764767 (1988-08-01), Ichikawa et al.
patent: 4951300 (1990-08-01), Koike
Shimoura Yoichi
Tsuchiya Yoshitsugu
Edmonds Warren S.
Kayaba Kogyo Kabushiki Kaisha
Strecker Gerard R.
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