Abstract: In implementations of a linear encoder force transducer, an encoder component generates light that enters a light input window of an encoder strip, and reflective surfaces disperse the light internally within the encoder strip. The encoder strip has etched lines formed cross-width of the encoder strip for emitted light that exits the encoder strip. The encoder component has gradated slots through which the emitted light from the encoder strip is detected by an array of photo transistors, each of the gradated slots corresponding to one of the photo transistors in the array of photo transistors. An encoder module can determine a linear displacement, such as representative of a force applied to a pen tip of a computer input pen, based on one or more of the photo transistors detecting the emitted light as the etched lines of the encoder strip move relative to the gradated slots of the encoder component.

Abstract: A system and method to adjustably create a reacting force in response to a vibrating force of a vibrating structure. The system includes an adjustable vibration absorber that creates a range of reacting forces. The method includes continuously monitoring the reacting force and the vibrating force with a sensor system operably associated with a control unit having an algorithm to determine if adjustment of the vibration absorber is required. If required, the control unit commands a driver to selectively adjust the vibration absorber such that the reacting force equals the vibrating force.

Abstract: An output control apparatus of a motor includes a controller formed by having a power device to bridge a motor and a power supply. The controller incorporating the power device provides voltage control modulation during different motor speeds so as to fix the recharging voltage at the DC bus in a specific range without involvement of any voltage converter. It is unnecessary to use additional complex circuits or other DC/DC converters to reduce the voltage recharged from the motor running at a high speed. In addition, space for the apparatus is reduced, and the specification and function of the original controller can be maintained without trading off work in redesigning the motor system.

Abstract: Photo-aging monitoring of light-based chemical indicators that experience performance degradation as the cumulative amount of light exposure from measurement and/or reference illumination increases from usage. Differing regions on a chemical indicator are illuminated with measurement illumination light of differing exposures, for example, higher brightness, longer exposure times, or both. Readings from the differing regions are compared with known aging information for the chemical indicator at issue to determine a confidence factor for the measurements. The confidence factor can be used to control various actions relating to measurements acquired from the chemical indicators, such as compensating measurement readings for photo-aging, assigning confidence levels to measurement readings, and issuing alerts to users when photo-aging exceeds one or more predetermined thresholds.

Abstract: An encoder signal processing circuit is connected to encoder heads outputting an encoder signal in accordance with a relative displacement with respect to a corresponding scale in such a way that signals can be transmitted to and received from the encoder heads, and processes encoder signals from the encoder heads. The circuit includes a processing unit and a processing decision unit. The processing unit generates displacement information from the encoder signal. The processing decision unit decides at least one of content of processing for the encoder heads and content of processing on encoder signals read from the encoder heads after starting to read an encoder signal from one of the encoder heads.

Abstract: A system and method for decoding quadrature signals includes a quadrature signal generator, a quadrature signal decoder, a key matrix and a driver. The quadrature signal generator generates quadrature signals on rotation. The quadrature signal decoder is configured to convert the quadrature signals into non-overlapping signals. The key matrix is configured to receive the non-overlapping signals. The driver is configured to scan the key matrix to decode the non-overlapping signals to generate an event update corresponding to a direction of rotation of the quadrature signal generator.

Abstract: Provided is a rotation detection device that detects a rotational direction and amount of a rotatable operation member. The detection device manages to reduce the rotation detection pitch while maintaining sufficient clearance for a rotation detection switch to operate. In other words, sufficient distance is given between rotation detection members such that the switch can accurately detect the movement from one member to the next. The rotatable operation member generally includes a plurality of switch driving sections that rotate in unison. A rotation detection switch generally includes a portion that moves in a first and second direction opposite to each other when coming into contact with the rotatable operation members, and is configured to output a detection signal at each movement. The switch and rotatable operation members are configured so that the movement direction of the detector is in a direction orthogonal to the circumferential direction of rotation.

Abstract: A signal sample trigger apparatus (206) comprises an input (302, 304), a processing resource (300, 500) coupled to the input (302, 304), and an output (306) coupled to the processing resource (300, 500). The processing resource (300, 500) is arranged to generate, when in use, a trigger signal (400, 600) in response to location increment information. The location increment information (402, 404, 602, 604) is received via the input (302, 304), and the trigger signal (400, 600) is provided via the output for triggering execution of a sample of an analogue signal.

Abstract: An encoder detects a relative displacement between an encoder scale and an encoder head. The encoder head incorporates a light source, a light-receiving element to receive light from the light source via the encoder scale, and a signal-processing circuit to process an electrical signal from the light-receiving element. The encoder has a signal detection unit, a signal discrimination unit, and a switching unit. The signal detection unit is activated selectively in accordance with setting. When activated, the signal detection unit detects one or more signals having an almost sinusoidal waveform from the encoder head. The signal discrimination unit is activated selectively in accordance with setting. When activated, the signal discrimination unit determines the waveform of one or more signals having an almost sinusoidal waveform from the signal detection unit. The switching unit switches the current to be supplied to the light source to one of various magnitudes.

Abstract: An encoder signal processing circuit includes: a plurality of detectors adapted to generate signals with different phases; a switching circuit adapted to alternatively select and output a signal from the detectors; and a waveform shaping circuit adapted to shape waveforms of output signals from the detectors that are switched by the switching circuit. The encoder signal processing circuit may include a direction determining/counting unit adapted to: (a) monitor output signals from the waveform shaping circuit in relation to an operation of the switching circuit, (b) determine a direction of movement and an amount of movement; and (c) calculate the amount of movement.

Abstract: A rotation position detecting device includes an angular signal generator which generates pulses the cycle period of which is even or equal when a rotating object rotates at a constant rotation speed and a non-pulse portion which corresponds to a reference position, an up-down command circuit for generating an up-down command signal the frequency of which is divided to a half of the frequency of the angular signal, a pair of first counters for counting up or down the clock signal when the up-down command signal changes from a first level to a second level to reset and subsequently counting down the clock signal when the up-down command signal changes from the second level to the first level, a pair of processing circuits for providing a first and second reference values, a pair of counters which generates detection signals when the counted number of the counters becomes smaller than the first or the second reference value.

Abstract: The present invention relates to an input method of encoder signals, and more particularly, to an input method of encoder signals which senses encoder signals by setting a predetermined signal sensing period at which the encoder signals to be input are sensed, and adjusts sensitivity according to the input of the encoder signals by using input period and number of times of the encoder signal. In the present invention, an output period of interrupt signals output from a microcontroller is set to be shorter than an output period of the encoder signals. In addition, for the control according to the operation of the encoder, the microcontroller determines an input period of the encoder signals and then determines whether the encoder signals are input continuously or discontinuously. If the encoder signals are continuously input, the sensitivity of the encoder signals is adjusted in order to select the next item in the initial state by counting the input number of times of the encoder signals.

Abstract: An apparatus and method for sensing a rotary switch handling direction of a monitor is disclosed, in which a simple configuration can be obtained and accuracy in sensing a handling direction can be enhanced. The apparatus for sensing a rotary switch handling direction of a monitor includes a rotary switch for outputting voltage levels varied correspondingly depending on a user's handling direction, and a microcomputer for storing the voltage levels output from the rotary switch and comparing the voltage levels with a previously stored voltage change/handling direction table to determine a handling direction of the rotary switch. Since the handling direction is sensed by the voltage level difference for respective contacts, it is possible to exactly sense the handling direction and to relatively obtain a simple configuration.

Abstract: An apparatus and method for sensing a rotary switch handling direction of a monitor is disclosed, in which a simple configuration can be obtained and accuracy in sensing a handling direction can be enhanced. The apparatus for sensing a rotary switch handling direction of a monitor includes a rotary switch for outputting voltage levels varied correspondingly depending on a user's handling direction, and a microcomputer for storing the voltage levels output from the rotary switch and comparing the voltage levels with a previously stored voltage change/handling direction table to determine a handling direction of the rotary switch. Since the handling direction is sensed by the voltage level difference for respective contacts, it is possible to exactly sense the handling direction and to relatively obtain a simple configuration.

Abstract: An apparatus and method for sensing a rotary switch handling direction of a monitor is disclosed, in which a simple configuration can be obtained and accuracy in sensing a handling direction can be enhanced. The apparatus for sensing a rotary switch handling direction of a monitor includes a rotary switch for outputting voltage levels varied correspondingly depending on a user's handling direction, and a microcomputer for storing the voltage levels output from the rotary switch and comparing the voltage levels with a previously stored voltage change/handling direction table to determine a handling direction of the rotary switch. Since the handling direction is sensed by the voltage level difference for respective contacts, it is possible to exactly sense the handling direction and to relatively obtain a simple configuration.

Abstract: A rotating body has paired anchoring projections and small projections projectingly disposed on one side thereof. On a shutter plate are formed guide holes in which the paired anchoring projections and small projections inserted in the shutter plate are slidable within a predetermined allowance angle range. When rotation input to a handle is broken during rotation input, the shutter plate is rotated respective to the rotating body in a direction opposite to the rotation direction of the rotating body within the allowance angle range, and the light transmission paths are closed by the shutter plate.

Abstract: An angular position/position encoder is provided for determining the position of a moving part through evaluation of the direction-specific changes in the measured values recorded and for serial output in binary form of the position determined in this way, wherein all changes in measured values are also added together, independent of the direction of movement, and then output as the result of the total distance or angle traveled.

Abstract: A positional encoder assembly including a positional encoder, an interface unit releasably connectable with the positional encoder for connecting the positional encoder with a data bus, and connection elements providing for connection of the interface unit with the positional encoder and for disconnection of the interface unit therefrom upon displacement of the interface unit relative to the positional encoder.

Abstract: A sensor system is provided in which a digital absolute value of the particular position of a stationary part (stator) with respect to a part moving relative to it (rotor) is created, which is transferred in serial transmission to an evaluation circuitry, whereby transfer of the serial absolute value is induced each time by an external signal. In order to increase the resolution of the encoder, the change in absolute value is recorded each time in the sensor and finest interpolation is undertaken beginning each time from the time of the change. Finally, the absolute value is amended by the accumulated result of finest interpolation when interrogated by the external signal.

Abstract: An angular position/position encoder is provided for determining the position of a moving part through evaluation of the direction-specific changes in the measured values recorded and for serial output in binary form of the position determined in this way, wherein all changes in measured values are also added together, independent of the direction of movement, and then output as the result of the total distance or angle traveled.

Abstract: A method, an apparatus and a computer program product are provided for accurately determining the vertical speed of an aircraft in a manner independent of signals provided by an air data computer, an inertial reference system and an inertial navigation system. Initially, a first vertical velocity of the aircraft is determined based upon a pressure altitude value associated with the aircraft. A second vertical velocity of the aircraft is also obtained from a GPS receiver carried by the aircraft. The first and second vertical velocities are then combined to determine the vertical speed of the aircraft. In this regard, the first and second vertical velocities are combined by complimentarily filtering the first and second vertical velocities. More particularly, the first vertical velocity is typically low pass filtered to remove high frequency noise that is attributable to the relatively low resolution of the first vertical velocity value.

Abstract: An apparatus and method for sensing a rotary switch handling direction of a monitor is disclosed, in which a simple configuration can be obtained and accuracy in sensing a handling direction can be enhanced. The apparatus for sensing a rotary switch handling direction of a monitor includes a rotary switch for outputting voltage levels varied correspondingly depending on a user's handling direction, and a microcomputer for storing the voltage levels output from the rotary switch and comparing the voltage levels with a previously stored voltage change/handling direction table to determine a handling direction of the rotary switch. Since the handling direction is sensed by the voltage level difference for respective contacts, it is possible to exactly sense the handling direction and to relatively obtain a simple configuration.

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: 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: The method and apparatus of the present invention is directed to architectures for signal processing, such as for performing analog-to-digital and digital-to-analog conversions, in which the source signal is decomposed into subband signals by an analysis filter, processed, and the processed subband signals combined to form a reconstructed signal that is representative of the source signal.

Abstract: A first value (V), which corresponds to the angular units covered during two actual position values successively transmitted via the data transmission link at the maximum rotational speed of the encoder shaft (W), and a second value (D) which corresponds to the difference between the maximum travel of the angular position encoder (MAX) and the first value (V), are stored in a store. A processing unit determines the direction of rotation of the shaft (W) depending on whether two actual position values (X11, X12; X21, X22; X31, X32) lie in the range between the zero point (NP) of the angular position encoder and an actual position value (L2) corresponding to the magnitude of the first stored value (V), or in the range between an actual position value (L1) corresponding to the magnitude of the second stored value (D) and the maximum travel (MAX), or outside these ranges.

Abstract: An apparatus and method for detecting the absolute position of a movable member, by monitoring the incremental and directional of movement of an indexed-encoder, coupled to the movable member, and comprising a single index space and a plurality of non-index spaces. The index space of the indexed-encoder member has a characteristic different than a characteristic of all of the other non-index spaces. The apparatus is capable of distinguishing the index space from any of the non-index spaces based on the characteristics of the index space and non-index spaces, and thus detecting when the index space or any of the non-index spaces is at the predetermined location.

Abstract: An apparatus is provided to determine the speed and direction of a rotating shaft, including a rotor with three circumferentially spaced teeth connected to the shaft. The spacing of the center of the second rotor tooth is wider than the spacing of the center of the first tooth and the spacing of the center of the third tooth is wider than the spacing of the center of the second tooth. A sensor detects the center of each tooth and produces a signal in response thereto. The signal is received by a computer. The computer determines the speed and direction of rotation of the shaft by determining a first time period to reach the center of the first tooth, a second time period to reach the center of the second tooth and a third time period to reach the center of the third tooth.

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: 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 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: 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: The present invention relates to a forward/backward counting device intended for providing an absolute address of N bits in binary code, the address enabling the position of an object to be deduced from two signals leaving a non-absolute position coder linked to the object. A device generates a first partial address expressed in code which differs from the binary code. A microprocessor is linked to the device and enables the first partial address to be transformed into an absolute address. The invention applies to robotics and metrology.

Abstract: A method of determining the direction of rotation of a member (17) is closed, wherein the member has a speed pick-up rotor (27) having a plurality of teeth or exciter surfaces (29). The rotor has a predetermined pattern of gaps (37,73) and groups of teeth, each group of teeth having a number of teeth which is different than the number in any other group. As the rotor rotates, the pattern of gaps and teeth is sensed, and compared to a predetermined pattern. Depending upon the results of the comparison, the logic generates either a signal (61) representing clockwise rotation, or a signal (65) representing counter-clockwise rotation.

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: The search position encoder includes a generally planar medium, a search probe and a device for moving the probe generally parallel to the surface of the planar medium, and indexing device for locating the actual position of the probe relative to a fixed location on the generally planar medium. A plurality of gratings consisting of alternating strips of conducting and non-conducting materials are arranged on or adjacent to the medium parallel to orthogonal axes of the medium, and a device for sensing the movement of the probe in a plane parallel to the gratings. The location of the probe may then be determined based upon the sensing of the passage of the probe relative to the gratings.

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: An auxiliary resolver position tracking (RPT) system for an industrial robot includes a resolver excitation and monitoring system which is powered by an uninterruptable power supply which includes a battery. The RPT system generates trapezoidal excitation pulses for the resolvers in the robot when no external excitation signal is applied, for example when the robot is shut down. Since there is relatively little motion to be detected in these instances, the RPT system switches between a slow position sampling rate, when no motion is detected, and a fast sampling rate when motion is detected. When operating on battery power, the RPT only switches to the fast sampling rate when motion is detected. To ensure that no motion data is lost when the system switches back to the slow sampling rate, the high sampling rate is maintained for a time sufficient to capture any residual motion of the robot.

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: 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: A rotary encoder which serves to generate absolute position data is outfitted with a power source monitor which generates, during a power interruption, an alarm signal which invalidates all subsequent absolute position data being outputted by the rotary encoder. Loss of output data from the rotary encoder is reliably prevented, even upon the unexpected occurrence of very short power supply interruptions. This enhances the operational reliability and stability of the encoder considerably.

Abstract: An improved encoder for indicating angular position or rotation of a shaft, and particularly a digital encoder for use with materials handling vehicles, includes an index mark in an index band of the encoder that is made wider than the marks in the data tracks. Associated detecting circuitry is responsive to the wide index mark for creating a dead band around a neutral position of the encoder to permit the free movement of the encoder shaft by an angular amount determined by the width of the index band. The wide index band enlarges the tolerance permitted in the return of the shaft to its neutral position and when installing the encoder on a shaft. When an encoder having a wide index band is used with a control handle, such as in positioning devices and accelerators on materials handling vehicles, the control handle has an improved feel and response.

Abstract: An electronic absolute coordinate encoder for positional control devices which includes an encoding section, a detector section, a counter section and a backup power source. The encoder can detect the current position of the positioning system continuously even in case of power interruption and thus the positioning system may not be returned to the original position for the purpose of performing the position control, when the power interruption ends.

Abstract: For the purpose of knowing an angular position and a rotational speed of a rotary body, according to an encoding pattern on an encoder mounted to and synchronously rotated with the rotary body, rotational angular position signals consisting of n-phase rectangular waves and sensing pulses occurring at a predetermined rotational angle interval are generated. In response to the issue of each sensing pulse, levels of the respective rotational angular position signals are detected, a variation pattern of a combination of the detected n levels is compared with a reference variation pattern, and it is determined whether an abnormal condition has arisen or not, and if the condition is normal, whether the variation pattern is a forward traveling pattern or a backward traveling pattern. In the case of the forward traveling pattern, (+1) is added to a rotational angle counter, while in the case of the backward traveling pattern, (-1) is added to the rotational angle counter.

Abstract: An operating device for inputting the coordinate positions of a controlled object that moves across a screen. The present invention is directed to obviating the problems of the prior art involving the bad operability of a knob which requires rotation through a large angle to move the controlled object across the screen, and the short life-span of the knob due to frequent use. In order to overcome these problems, the rotational number of a main shaft is increased by a rotational number increasing mechanism and the rotational number of the output shaft of the rotational number increasing mechanism is optically or magnetically detected. The present invention is therefore suitable for use as an operating device for a TV game machine.

Abstract: A high-resolution shaft encoder and a related encoding method for accurately measuring angular position and velocity of rotating shafts. The high-resolution shaft encoder includes an annular-shaped actuator ring that rotates at high speed, a shaft centered within the actuator ring, and an encoder housing. The shaft encoder generates measurements of shaft position .theta..sub.p and velocity .omega..sub.p, with respect to the encoder housing, from measurements of three time intervals t.sub.p, t.sub.r and .DELTA.t. These time interval measurements are computed from the output of a sensor element positioned on the shaft and a sensor element positioned on the encoder housing, both of which respond to an input actuation element positioned on the rotating actuator ring.

Abstract: The present invention relates to an optical laser analog-to-digital (A/D) converter and the use of such a converter as a transducer. In a first embodiment of the invention, the converter consists of a source which produces a coherent beam of light that is passed through a lens system to produce a line or bar of light. The bar of light passes through a coded optical mask which is made of a thin transparent material with a binary or gray code printed thereon. The mask is mounted to an object whose movement is to be detected. The mask may also be configured in the form of a circle and mounted to a motor shaft to sense motor rotational displacement, RPM or velocity. As the mask moves, the imprinted pattern changes according to the coding on the mask. The portion of the light that passes through the mask strikes the target of a moving recording media.

Abstract: An absolute displacement detector utilizing two sensors and a code bearing track having domains arranged such that relative movement between the sensors and the track produces two signals in phase quadrature which are processed with digital circuitry to provide displacement data indicated by a multiple bit digital word whose higher bits indicate number of domains passed and whose lower bits indicate position within a domain.