Abstract: An apparatus and method for the multiple detection of optoelectronic signals, especially for detecting the positions of setting elements of flaps, slides, valves, etc. arranged in motor vehicles, to determine the steering angles for controlling driving dynamics, or to determine rotational angles or a linear movement converted into a rotational movement. At least two signal paths extend at an angle relative to one another, with one signal path extending substantially parallel to and under a clock disc and with the second signal path intersecting a sensor element perpendicularly through the clock disc. Signals in the first signal path are deflected by a reflector element underneath the clock disc in the direction towards the sensor element where the coincide with signals in the second signal path.

Abstract: An electronic circuit for measuring the position of a spatially periodic intensity pattern of incident radiation includes an array of detectors (1); two or more correlator units (2, 3) each having arrays of capacitors (12, 13) connected to a buffer (14); and a phase angle computing unit (4). The pitch of the array of detectors (1) is smaller than the pitch of the incident intensity pattern so that the latter is oversampled, yielding high accuracy. The detector outputs (17) are weighted by respective fixed capacitance values (15, 16) which vary periodically along arrays of capacitors (12, 13), and a weighted sum of outputs for each correlator unit (2, 3) is output at its respective buffer (14). The capacitance values (15, 16) of respective correlator units (2, 3) are mutually offset by a predetermined phase shift. The analog computation using capacitor arrays (12, 13) is fast and energy efficient, and can be implemented as a VLSI circuit.

Abstract: A position measuring system that includes a scale having an incremental track, which extends in a measuring direction and has an incremental graduation with two different graduation periods. A scanning unit moves in relation to the scale in a measuring direction, the scanning unit has an incremental signal detection arrangement, wherein the incremental signal detection arrangement generates incremental signals with a first coarse signal period and generates incremental signals with a second finer signal period.

Abstract: An incremental rotary encoder having first and second sensors which each output two sine wave signals having a phase difference of 90 degrees while a rotary member of the incremental rotary encoder rotates. The incremental rotary encoder includes an absolute-zero-index detecting device, provided for the first sensor; at least one binary coding circuit which codes each of the two sine wave signals and the zero index signal into a corresponding binary signal; a holding device for holding the level data of the binary signal of each sine wave signal output from the second sensor when the absolute-zero-index detecting device outputs the zero index signal; and a controller for determining whether the phase of the two sine wave signals output from the second sensor advances or delays with respect to the phase of the two sine wave signals output from the first sensor.

Abstract: A method and computer program product are provided for implementing text conversion table compression. For implementing text conversion table compression, a character sequence is loaded from a full-size conversion table. The character sequence is checked for one of plurality of character patterns. Responsive to identifying one of the plurality of character patterns, the character sequence is compressed into a compressed conversion table for the identified one character pattern. Responsive to failing to identify one of the plurality of character patterns, the character sequence is copied into the compressed conversion table. The character sequence from the full-size conversion table is checked for one of the plurality of character patterns including a repeating character sequence, a ramping character sequence, and a repeating high byte character sequence.

Abstract: An absolute-value encoder device for detecting a plurality of rotation quantities is disclosed. An A/B phase forming portion 610 forms an A-phase pulse signal and a B-phase pulse signal, based on light passing through a slit rotating together with a rotary shaft. One period of each of those pulse signals corresponds to one revolution of a rotary shaft. The A- and B-phase pulse signals are displaced in phase by 90° from each other. When an A/B-phase state detecting portion 640 detects a state change of each of those pulse signals, a clock forming portion 66 changes a frequency of a clock pulse signal to another frequency.

Abstract: A method of decoding a quadrature encoded signal where position tracking is implemented which decouples the position calculations from the encoder edges. In one embodiment of the present invention, a uni-directional pulse accumulator is used to count encoder edges, and a periodic interrupt timer is used to update the position information, where interrupts are generated independent from encoder edges. At slow speeds, the mode switches to monitor each encoder edge to check for direction reversal without requiring position information. This decodes bi-directional quadrature position information using a uni-directional counter and a count compensation method for resolving changes in direction.

Abstract: A linear position encoder is provided which is not affected by ambient light, smoke, moisture, particulate matter, and also not affected by electrical interference such as may be caused by stray fields or permanent magnets or magnetic particles. The encoder comprises a linear scale having an excitation loop disposed along the length of the scale and having electrical terminals preferably disposed at one end of the scale. An alternating current is applied to the excitation loop to create an alternating magnetic field. At least one periodic conductive pattern is provided on an outer side of the excitation loop. The periodic pattern has electrical terminals preferably at the same end of the scale as the terminals of the excitation loop. A sensor is provided on a small printed circuit card that is movable in relation to the scale. The card has a pickup loop which receives energy coupled from the scale excitation loop and which induces current in the periodic pattern.

Abstract: A position measuring system for the determination of the relative positions of two objects which can be moved with respect to each other, as well as a process for operating the same are disclosed, which in case of a relative movement provides at least one pair of phase-shifted analog incremental signals, and which makes possible a definite variation of the signal periods (SP) by at least one signal period variation factor (n) of the analog incremental signals transmitted to an evaluation unit arranged behind it by a signal period variation unit. The signal period variation unit furthermore comprises correction means for eliminating most varied errors in the output signals (SIN′, COS′). Among these are counted errors possibly resulting during the signal period variation, as well as measurement arrangement-specific errors.

Abstract: An error detection method for use with a two channel increment encoder. The error detection method operates to detect errors over a wide range of rotational velocity of a rotating member. The error detection method employs the signal from one or two of the channels of the encoder and determines if pulse edges from the signals deviate from expected normal behavior. When an error is detected, actions can then be taken by the controller for the rotating member to prevent undesired results.

Abstract: A rotor position encoder is provided for an electrical machine having a rotor and a stator, the encoder including a coded disc having teeth of widths that vary in a repeating sequence and being arranged to rotate with the rotor past a sensor which outputs a signal corresponding to the coded sequence. By comparing the coded signal with an internally generated signal the position of the rotor can be determined at a first resolution level. In addition, a counter is enabled as each tooth is sensed and provides a second output signal at a higher resolution level indicative of the rotor position between successive teeth. For a multi-phase machine, a value representative of the rotor position relative to each phase is combined with the value representative of the incremental position common to all phases. High resolution rotor position encoding with simplified logic is thus provided.

Abstract: The present invention provides a method and apparatus for monitoring an infusion pump (10). The method and apparatus provides an encoder (101) which is used with a motor (65) of the infusion pump (10) and a monitoring method which effectively provides rotational directional information. The present invention utilizes a state transition of a first switch (111) indexed against a constant signal from a second switch (113) corresponding to the center of a flag (117) or sector (119).

Abstract: A signal control apparatus includes an electrically resistive strip (4) allowing close proximity of a finger. A signal can be coupled into the strip, and a signal output (V1) can be detected at one end of the strip. The structure (1, 3) for coupling a signal into the strip (4) produces a high frequency signal in the strip and a signal output (V2) can be detected at the other end of the strip. These outputs (V1, V2) are dependent, in use, on the position along the strip of a finger in close proximity thereto and provide, by capacitive coupling to the strip (4), a leakage path for some of the signal. The last position of a finger along the strip (4) can be visually indicated when that finger has been removed. The strip (4) is on the underside of an insulating plate (10), the upper side of which has a path (11) for a finger to follow.

Abstract: In the installation of a scanner of a position measuring apparatus, it is required that parameters such as amplitude and phase position of analog signals generated by a scanner be tested so that the scanner can be correctly installed. For this purpose, a control device with a display field is provided. In the display field, a bar is displayed whose width represents a measure for the range of variation of the radius and whose position represents a measure for the average radius of a Lissajous figure. In addition, a marking is displayed for the admissible range of variation of this radius.

Abstract: A position encoder system is provided, the system employing a medium having a track with incremental markings which define an embedded reference position identifier. Upon movement of the medium, a sensor detects passage of the incremental markings, each such marking being indicative of a predetermined movement of the medium. The sensor also detects the embedded reference position identifier, and correspondingly, provides a recognizable index pulse for use in determining an absolute position of the medium.

Abstract: A method and apparatus to convert absolute angular or linear position to digital information utilizes a ternary coding scheme. The code is arranged along a single track. Sensors placed at essentially equal intervals distinguish three states per position. The sensor outputs are converted from ternary to binary data by combinatorial logic. The sensors may be mechanical contacts, optical detectors, magnetic detectors, or capacitive detectors. Such an encoder may be used as a potentiometer, multiposition switch replacement, shaft encoder, or length measurement device.

Abstract: A signal modulation method comprising receiving at least first and second synchronized incoming streams of complex symbols, thereby to define a plurality of incoming vectors each including at least first and second synchronized complex symbols, mapping each complex symbol into a signal component comprising a linear combination of an in-phase signal and a quadrature signal, the quadrature signal comprising a Hilbert transform of said in-phase signal, wherein all of the signal components are substantially mutually orthogonal and wherein the frequency spectrums of all signal components mapped from a single incoming stream are centered around a common frequency location which is unique to the single incoming stream and wherein the frequency spectrums of signal components mapped from different incoming streams having adjacent common frequency locations are partially overlapping and wherein signal components mapped from sequential incoming symbols partially overlap in time and combining all of the signal components

Abstract: An absolute linear encoder includes an index channel and at least two counter channels. The spacing between markings on the index channel is constant, and the spacing between markings on the first and second channels is predetermined so that the positions of the markings in the first and second channels vary so as to provide a unique signature for each position along the encoder. The linear encoder includes quadrature channels to provide increased resolution and to determine the direction of translation. The encoder is provided with a detector unit to detect positions of the markings in each channel, and a processing unit to calculate an absolute position from the detected marking positions. A method of producing the absolute linear encoder includes selecting spacings for markers in the quadrature, index, first and second channels in order to provide a desired resolution and encoder length.

Abstract: In a device for detecting a position of an object (linear or circular strip) moving in rotation or translation relative to a base, an incremental track bearing periodically recurring marks and two index tracks bearing a plurality of index marks are scanned by sensors. These sensors supply analog signals which are complementary to each other. In each case, two complementary signals are combined to form a logical track. By a combining of the logical tracks with each other, a further logical track is formed which contains a serial code which corresponds to the absolute value of the position of the object.

Abstract: A position encoder system is provided, such system including a code wheel, a pair of sensors, a counter, and a processor capable of identifying the correlation between separately identified markings of the code wheel. The identified correlation is indicative of code wheel accuracy, and thus is used to correct error in any angular position determined using the code wheel.

Abstract: A code plate has an m-bit signal track read out in parallel for providing the starting position of an AC servo motor for commencing rotation when power is first turned ON. An n-bit signal track accompanied by an incremental signal track is provided on the code plate with the n-bit track read out serially, converted to pure binary in parallel, and used once rotation of the servo motor commences to provide the initial absolute value of the encoder. To this n-bit initial value is added signals from the incremental track upon continued rotation of the code plate.

Abstract: An apparatus for monitoring a rotating member. The apparatus includes a grating pattern having a plurality of wedge shaped pattern markings which are monitored by a sensor for generating a pulse signal. A processor calculates the rotating speed and the axial position of the rotating member as a function of the generated pulse signal.

Abstract: A coder includes a measuring rule (R3) carried by one object and having at least two tracks (X, Y). The tracks are provided with simple marks distributed in a substantially identical manner over the two tracks. At least two specific marks (M1, M2) are located on two distinct tracks. Each mark limit defines a spacing change on the measuring rule. At least two mark readers (LX, LY) are carried by another object, each associated with a track whose marks it detects. A processor is connected to the readers for determining the distance and direction of the movement. The invention is useful in robotics and metrology.

Abstract: The present invention relates to an electronic meter circuit for a time comparison measurement between two successive periodic events with which the signal time ratios between two times two successive events can be recognized by a simple method.The electronic meter circuits comprises a reference meter to be loaded with a reset value when a first event occurs and for reference meter to start to count at a clock frequency and when a second event occurs, reference meter starts to count in the opposite direction at a clock frequency until a third event occurs, and when the third event occurs, meter reading forms a reference value for the ratio of the signal times between the occurrence of the first and second events and between the second and third events.

Abstract: A sensor failure detection circuit for a position encoder, the sensor failure detection circuit receiving from a first set of at least one position sensor position signals which change state at a high resolution and from a second set of at least one position sensor position signals which change state at a lower resolution, the detection circuit monitoring a count for the position signals at the high resolution between states of the position signals at the lower resolution and comparing the count with a predetermined range which represents an expected count for the position signals at the high resolution between the states of the position signals at the lower resolution.

Abstract: A position detecting apparatus and method of determining the detected position utilizing a motor driven incremental encoder to provide a signal indicative of a plurality of reference points and a moving mechanism connected to the output shaft of the motor with a sensor for detecting a plurality of division points wherein the sensor and the detected division points are moved relative to each other. The plurality of division points may be provided at equal intervals, the range of output shaft motion can be detected in the form of interval positions by detecting and measuring the output pulse count from the incremental encoder and detecting the amount of movement via the division points detected by the sensor. Using the relation between the predetermined positions of the division points of the moving mechanism and the known positions of the reference points of the incremental encoder, the absolute value of the position of the output shaft can be precisely determined.

Abstract: An absolute encoder which is operative to provide a plurality of signals indicating a current position, that signal including a least significant bit whose edge is detected and used as a basis for adjusting the current value under a variety of circumstances, typically based on the speed of the encoder. If the encoder is operating at high speed, a predetermined value may be assigned to the current position, while if operating at low speed, the value may be edge settable at least once at speeds below a limit value.

Abstract: A digital absolute position encoder is provided for determining absolute position of a first member with respect to a second member. The absolute position is determined within a resolution cell of L/2.sup.n, where n is an integer and L is a predetermined span. One of the members has a plurality of, m, tracks of binary indicia distributed over the predetermined span, L, where m is an integer less than n. The other member has a plurality of indicia detectors disposed on the second member for detecting the binary indicia. With such an arrangement, an encoder is provided having "a unit-distance code", yet uses less tracks than that used with a conventional Gray code encoder. Further, the encoder has a reduced number of transitions than that required on the track used with a conventional Gray code encoder. Both of these features simplify the design and fabrication for a given encoder resolution.

Abstract: An encoder includes a code plate, a detector, a transformer, and first and second calculators. The code plate is formed with an absolute pattern including a plurality of bit patterns, each bit pattern formed by a predetermined number of bits and representing one absolute position. The detector moves relatively with respect to the code plate, has a plurality of detecting elements arranged to be opposed to the predetermined number of bits, and reads the bit pattern from the absolute pattern to output a bit pattern signal representing the bit pattern. The transformer can transform only specific bit pattern signals corresponding to specific bit patterns out of a plurality of the bit pattern signals corresponding to the plurality of bit patterns, into the absolute positions. The first calculator calculates a relative, positional relation between the bit pattern corresponding to the bit pattern signal, read from the detector, and the specific bit pattern.

Abstract: In a system and a method for determining the speed gradient dn/dt of a shaft of an internal combustion engine, the speed gradient dn/dt is determined as a function of the third power of the speed and the difference between two segment times in the control device. The speed gradient is only determined in phases which are not time-critical, while segment times are read in or stored only in time-critical phases so that the data required for controlling and regulating the internal combustion engine can be calculated in these time-critical phases independently from the determination of the speed gradient.

Abstract: A method and apparatus to convert absolute angular or linear position to digital information utilizes a ternary coding scheme. The code is arranged along a single track. Sensors placed at essentially equal intervals distinguish three states per position. The sensor outputs are converted from ternary to binary data by combinatorial logic. The sensors may be mechanical contacts, optical detectors, magnetic detectors, or capacitive detectors. Such an encoder may be used as a potentiometer, multiposition switch replacement, shaft encoder, or length measurement device.

Abstract: A device and method for monitoring the angular displacement of a rotating shaft provides an ultrasonic transceiver reflecting pulses off of a reflecting edge of a vane of a rotor affixed to the shaft. The reflecting edge is configured in the profile of an involute curve so that changes in the time delay between transmission and reception of each reflected pulse, which correspond to changes in the distance between the transceiver and the reflecting edge, are linearly related to changes in the angular displacement of the shaft, and arranged such that the reflecting edge is normal to the probe axis so that the energy is reflected back to the probe. A circular disc may be associated with the vane to provide a reference reflected pulse, which eliminates errors which might occur due to wobbling of the shaft.

Abstract: The absolute encoder utilizes two or more sensors per track and the output of each sensor is modulated by the track to generate a multiphase analog signal from each track. An analog to digital converter converts each analog signal to a digital value. The multiphase cyclic digital values are combined into a single linear output per track that increases linearly from zero to a maximum over the full span of the measuring scale. Corrections are made for zero drift in the analog signals, for changes in amplitude (gain) of the analog signals and for deviations in the linear values from a perfect straight line. When measuring rotary displacement the methods disclosed may be used to combine the outputs of the geared scales.

Abstract: An absolute encoder has a code plate formed with an absolute pattern and an incremental pattern. A first detector detects the absolute pattern, and outputs an absolute signal. A second detector detects the incremental pattern, and outputs an incremental signal. The absolute encoder stores the absolute signal according to an external input signal, and forms a corrected absolute signal on the basis of the incremental signal input after the absolute signal is stored.

Abstract: An apparatus for detecting the angular position for an internal combustion engine is capable of accurately detecting the angular position by a simple structure without being influenced by changes in the period of angular position signals due to inaccuracy of rotor contour and a change in rotational speed. Up-down counters up and down count clock pulses in response to the pulse train from a rotation sensor for determining information on unequal interval corresponding to a reference position in the pulse train. The frequency of the angular position is divided by a frequency dividing circuit. Up-down counting of clock pulses by the first and second up-down counters is terminated within two periods of the angular position signal. The outputs of the first and second up-down counters are alternatively up counted and down counted every one period of the angular position signal to determine the reference angular position based upon any one of determination outputs from up-down counters.

Abstract: A position-encoded screw, and a method and system for calibrating a position-encoded screw. In one embodiment, the screw includes a threaded portion and a set of position-encoding marks arranged along a spiral path around the threaded screw portion. To calibrate the screw, a set of sensors detects each mark as the screw is incrementally advanced past the sensors, and the absolute position of the screw is independently measured using an auxiliary device such as a precision electro-optic scale. The output of the sensor set is processed to generate encoded position signals representing encoded displacements of the screw relative to a known position. A set of the independently generated absolute position signals, one corresponding to each encoded position signal, is stored in the form of a look-up table, so that each absolute position signal may be read from the table in response to a corresponding encoded position address signal.

Abstract: The present invention relates to a rotary encoder for detecting a rotational angle. A rotary encoder according to the present invention comprises a rotating body provided on its surface with a plurality of digital code patterns representative of absolute angle ranges and a plurality of relative angle patterns representative of relative angles, a high-order angle data producing means (1,2,5,7) for reading the absolute angle patterns to produce high-order angle data, and a low-order angle data producing means (1,2,5,7) for reading the relative angle patterns to produce low-order angle data. The rotary encoder according to the present invention ensures medium resolution by means of the digital code patterns and attains finer resolution by means of the relative angle patterns, whereby the rotational angle can be detected with superior resolution.

Abstract: An apparatus is provided for generating a pulse train, the apparatus comprising a member having a plurality of spaced marks disposed thereon with at least one of the spaced marks being a reference mark. The member is in communication with means for generating the pulse train as the plurality of spaced marks move. Additionally, the pulse train has a periodicity defined by the same edge of two successive pulses and the plurality of spaced marks are configured so that the periodicity of the pulse train remains constant.

Abstract: A circuit compensates backlash of a shaft on an incremental encoder having a quadrature and index pulse output lines. Quadrature is represented as two signal lines phased apart by 90 degrees and an index pulse occurring once per revolution of the encoder shaft. The logical combination of the quadrature signals produce a four state condition which, through sequential examination of the signal levels, allows discriminating circuitry to determine the rotational direction of the encoder shaft. The circuit allows the definition of clockwise or counterclockwise rotation as being the forward direction. When the circuit discerns the positive forward rotational progression of the two signal lines, the circuit passes such signals unaltered to a pulse responsive system. Upon discernment of an encoder's shaft reverse rotation, the circuit causes the last forward rotational quadrature state to be latched on its output lines.

Abstract: Two fragments from a single maximal length sequence of length 2.sup.(x/2) -1 are interleaved to produce a new sequence of bits. The lengths of the fragments are such that they have no common factors. Each x-tuple of successive bits of the new sequence of bits uniquely defines the absolute position of that x-tuple in the sequence of bits, which position may be obtained from the relative position in the fragments of two y-tuples making up the x-tuple.

Abstract: An electronic postage meter is disclosed which includes a plurality of print devices each individually settable to a desired position so that the print devices may print a desired postage value; a plurality of d.c. motors, one for each of the plurality of the print devices, a different one of the d.c. motors being coupled to a different one of the print devices for setting the respective print device to a respective desired position; actual position sensing means for providing signals related to the actual positions of the print devices; and a microcomputer coupled to the d.c. motors and to the actual position sensing means. The microcomputer in response to signals from the actual position sensing means, a desired postage value and programming of the microcomputer sequentially controls the d.c. motors to set the print devices to respective desired positions for printing the desired postage value.

Abstract: A digital height encoder on a turret stockpicker is used to determine platform height. A pair of fixed reference switches are provided, one to reset a digital height memory to a predetermined height value each time the switch transitions either on or off, the other at a predetermined height near the staging point of telescoping masts for initial calibration of the encoder and for verification of proper operation during normal operations. If the height measurement indicated by the encoder upon the transition of the second or verificaiton switch is not within predetermined limits, an error signal is generated and recalibration will be required. Motion of the platform is also required if the control handle is in the upward direction and the platform has not reached its predetermined upper limits.

Abstract: A position encoder for monitoring the position of a robot arm includes an incremental encoder section which can be initialized locally by an initialization section. The initialization section comprises three engaged encoder gears with relative prime number of teeth, e.g., 23, 24 and 25, so that respective index apertures of the gears precess with successive revolutions of the gears. Upon startup, the robot arm can be moved sufficiently for all three apertures to be detected so that their relative phase positions can be determined. The relative phases can be used to determine an absolute initialization position. Once this initialization position is determined, robot motions can be tracked using the incremental encoder section.

Abstract: An magnetic encoder includes a multipolar magnetic body having a row of alternate North and South poles of equal widths, and a magnetoresistive element diposed in confrontation to the multipolar magnetic body. The magnetoresistive element includes at least one A phase magnetoresistive element member and at least one B phase magnetoresisitve element disposed in juxtaposition over ##EQU1## where n is an integer greater than or equal to 1, and .lambda. is a width of each individual pole of the multiplar magnetic body. Each of the A phase magnetoresistive element members and the B phase magnetoresistive element member has a group of series connected linear conductors arranged side-by-side into a comb-like shape.

Abstract: An incremental position encoder and method are disclosed herein for a close loop position control system, for example, for positioning a printing device in an electronic postage meter. The incremental position encoder and method includes three channels, first and second of which provide signals for coarse position determination and first or second and third of which provide signals for fine position determination.

Abstract: A resolution enhancement circuit comprises a voltage divider used to add multiples of two position representing quadrature signals into a plurality of adder output signals having zero crossings during the cycle of the quadrature signals, a digitizer creating a plurality digital signals based on the individual adder output signals and an output logic circuit combining the digital signals into a new pair of digital quadrature signals of increased resolution. The circuit provides information for more precise control of die casting machines and the like.

Abstract: An absolute encoder for detecting the absolute (as opposed to the relative) rotational displacement of an encoder shaft includes a pair of pitch signals recorded on tracks and an associated signal processing circuit. The pair of pitch signals have different periods (wave lengths) which are such that they have no common factors. The signal processing circuit includes magnetic sensors for producing absolute position data indicative of the degree of displacement of the encoder shaft, on the basis of the pitch signals. Through the use of a pair of pitch signals having periods with no common factor, a high degree of resolution is obtained, without having no significantly increase the number of pitch signal tracks.

Abstract: A position measuring apparatus of the type that includes a measuring scale and a scanning unit is provided. The measuring scale includes a measuring graduation track and a reference mark track associated with the measuring graduation track. The reference mark track includes a plurality of reference marks, a predetermined number of which are further designated as marked or unmarked. The scanning unit provides for scanning the measuring scale and evaluating the signal produced by such scanning. The apparatus also includes an operating switch associated with the scanning unit. The operating switch provides for selection of at least two modes of operation of the scanning unit: a first mode in which all the reference marks on the reference mark track are evaluated, and a second mode in which marked or unmarked reference marks on the reference track are evaluated.

Abstract: A measuring device is provided in which a graduated plate is scanned in at least two scanning locations. The scanning signals from the different scanning locations are transmitted to a testing circuit which determines whether the phase displacement between the scanning signals exceeds a limit value. If the limit value is exceeded, one of the scanning locations is weighted higher than the other. The weighting is implemented by increasing the components of the signals from one scanning location while decreasing the components from the signals from the other scanning location.

Abstract: A linear encoder has a plurality short main scales arranged separately in their longitudinal direction and plural sliders situated in parallel with the longitudinal direction so as to more along these main scales. In operation, data obtained through these sliders are joined and processed in a signal processor in order to get position data of a table. Consequently, any position along a long movement stroke of the table can be detected easily and at a low cost.