Abstract: A method for signal error correction of a position signal relating to a relative position of at least one sensor with respect to a reference, includes determining a set of parameter values of a parameterized approximation of a corrected relative position with respect to time based on measurements of the position signal over a duration of at least one period of a periodic signal error of the position signal. The method further includes estimating a first corrected relative position at a first time based on the parameterized approximation using the determined set of parameter values and the first time.

Abstract: The present disclosure is directed toward a method for measuring a true concentricity of a rotating shaft. The method includes simultaneously measuring, with diametrically opposed position sensors, opposite sides of the rotating shaft at an initial state to acquire a first measurement data and at a 180-degree rotation to acquire a second measurement data. The method further determines a rotational centerline and a shaft centerline based on the first and second measurement data, and calculates a concentricity error of the rotating shaft based on the determined rotational centerline and the shaft centerline.

Abstract: An image stabilization apparatus for a lens apparatus that moves an image stabilizing lens perpendicularly to optical axis includes a fixed barrel, a lens moving frame holding the image stabilizing lens and movable relative to the fixed barrel perpendicularly to the optical axis, an actuator that drives the lens moving frame relative to the fixed barrel, and the encoders used to determine the position of the lens moving frame relative to the fixed barrel. Each encoder includes a scale fixed to either the lens moving frame or the fixed barrel and a detector fixed to the other, the scale is arranged so that its grating is arranged in a radial direction about the optical axis so that the encoder has sensitivity to radial displacement of the lens moving frame about the optical axis which is higher than sensitivity to rotational displacement of the lens moving frame about the optical axis.

Abstract: An optical encoder of the present invention includes a light-receiving element unit 5, moving slit 2 and fixed slit 3. The light-receiving element unit 5 includes a pattern 5B for detecting infiltration of liquid.

Abstract: A position detection apparatus detects a position of an object, and the position detection apparatus includes a detector, a scale having a periodic pattern, the scale and the detector being movable relatively to each other, and a signal processor configured to generate a reference signal indicating a reference position of the scale, and the signal processor is configured to generate the reference signal based on a ratio of a first phase signal and a second phase signal from the detector.

Abstract: An optical encoder disk comprising an opaque disk, an outer track adjacent a peripheral edge of the disk, an inner index track defined by a first pattern of radial light-blocking elements subtending an arc within an annular band interposed between the outbound track and an axis of the disk, and an opaque support pattern of non-radial elements located within the annular band outside of the arc in which the index track is located formed of substantially non-radial elements. The inner index track further includes pattern apertures formed through the disk between the light-blocking elements so that light emitted on one face of the disk passes through the pattern apertures and falls upon photodetectors located adjacent an opposite face of the disk.

Abstract: A pattern wheel driver is provided. The pattern wheel driver includes a rotatable pattern wheel with patterned regions repeatedly formed on the pattern wheel. Each of the patterned regions has a plurality of patterns. Each of the plurality of patterns has a different width. The pattern wheel driver also includes a detector for detecting the plurality of patterns, mounted at a position where the patterned regions of the pattern wheel pass when the pattern wheel rotates. The pattern wheel driver also includes an encoder for producing a signal indicating whether the pattern wheel rotates in a forward direction or a reverse direction based on signals produced by the detector.

Abstract: A scanning system includes a synchronizing arrangement including a light guide and a photosensor. The light guide directs a light beam to a photosensor, wherein light is deflected by one or more moving elements in the scanning system into a scanning region. The light guide has a light entry region, a reflecting region for reflecting light entering the light entry region and one or more light exit faces, so that light entering the light guide through the light entry region is at least partly reflected in the reflecting region and exits through one of the exit faces. The shape and the properties of the light guide are such that for two pencils of light rays, a first pencil of light rays is spaced from the second pencil and is non-overlapping with said second pencil of light rays.

Abstract: A two-dimensional absolute encoder includes; a scale on which marks are arranged at predetermined pitches along first and second directions; a detector configured to detect a number of marks arranged in each direction; and a processor configured to obtain an absolute position of the scale in the each direction based on outputs from the detector. Each mark has one of characteristic corresponding to information of a quantized code used for indicating a position in the each direction. The processor is configured to generate a code sequence including the number of codes based on detection of the number of marks and information corresponding to the characteristic, and to obtain an absolute position of the scale in the each direction based on the code sequence.

Abstract: Disclosed are various embodiments of circuitry and methods for generating interpolated signals in an optical encoder. The optical encoder configurations and circuitry disclosed herein permit very high resolution reflective optical encoders in small packages to be provided. Methods of making and using such optical encoders are also disclosed. According to one embodiment, the interpolated signals are generated through the use of signal generation circuitry, peak voltage generation circuitry, reference voltage generation circuitry, slope detection circuitry, and a clocked comparator that is configured to output interpolated output pulses.

Abstract: A motor may be configured to drive a drive shaft and an engagement member supported on the drive shaft. A detectable feature comprising a rotary member may be supported on the drive shaft such that movement of the drive shaft by the motor changes a state of the detectable feature. At least one sensor may be arranged to detect the state of the detectable feature. Circuitry may be configured to provide a signal in response to a change in the state of the detectable feature detected by the at least one sensor.

Abstract: A miniaturized optical encoder capable of obtaining a sufficient amount of light in the light receiving element is provided. An optical encoder 1 includes a scale 2 having a scale track 2? and a readhead 3 having a light source 31 that emits light to the scale track 2?, a scale-side lens 32 that transmits the light emitted from the light source 31 to the scale track 2?, and a light receiving element 33 that receives the light reflected by the scale track 2? through the scale-side lens 32. The light source 31 is arranged between the scale-side lens 32 and the light receiving element 33. An optical axis Lsrc of the light source 31 is matched with an optical axis Ls of the scale-side lens 32 in a reading direction of the scale 2 and is separated from an optical axis Ls of the scale-side lens 32 by a predetermined distance D in a direction perpendicular to the reading direction of the scale 2.

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: A method and apparatus for suppressing loss of scale image contrast due to interference effects from optical path length differences, including lens profile aberrations, are provided in a displacement sensing optical encoder that uses a telecentric imaging configuration. According to the invention, the encoder is configured such that the image light that reaches the detector comprises symmetric ray bundles concentrated symmetrically on opposite sides of the optical axis center at the limiting aperture of the telecentric imaging configuration. Central ray bundles, and/or other ray bundles that have an optical path lengths significantly different than the operational symmetric ray bundles are prevented or blocked. As a result destructive interference is prevented and image contrast is improved.

Abstract: Provided is a rotary encoder, including: a rotary scale, which has a predetermined pattern including continuous patterns and a rotational angle original point formed thereon with reference to a pattern center, has a polygonal outer shape, and has the rotational angle original point defined with reference to at least one side of sides of the polygonal outer shape; a hub, which includes projections for abutting the sides of the polygonal outer shape of the rotary scale and positioning the rotary scale; a rotating shaft, which is press-fitted into the hub and rotates coaxially with the pattern center of the rotary scale; and detecting units for irradiating the rotary scale with light and detecting the light reflected by the rotary scale.

Abstract: A displacement detecting device comprises: a light source, a first beam splitter adapted to split the light emitted from the light source into a first beam and a second beam, a reflecting member adapted to reflect the first beam, an objective lens adapted to condense the second beam on a surface-to-be-measured, a first light receiving section adapted to receive interference light of the reflected first beam and the reflected second beam, a relative position information output section adapted to output relative position information in height direction of the surface-to-be-measured, a second beam splitter adapted to extract a part of the reflected second beam, an astigmatism generator adapted to generate astigmatism in the extracted second beam, a second light receiving section adapted to receive the second beam having astigmatism, and an absolute position information output section adapted to generate absolute position information in height direction of the surface-to-be-measured.

Abstract: Provided is a rotary encoder, including: a rotary scale, which has a predetermined pattern including continuous patterns and a rotational angle original point formed thereon with reference to a pattern center, has a polygonal outer shape, and has the rotational angle original point defined with reference to at least one side of sides of the polygonal outer shape; a hub, which includes projections for abutting the sides of the polygonal outer shape of the rotary scale and positioning the rotary scale; a rotating shaft, which is press-fitted into the hub and rotates coaxially with the pattern center of the rotary scale; and detecting units for irradiating the rotary scale with light and detecting the light reflected by the rotary scale.

Abstract: An optical encoder and method for measuring displacement information using an optical encoder uses an encoder member with multiple digital diffractive optic regions to optically diffract an incident beam of light to produce output beams of light having intensity distribution patterns, which are used to generate electrical signals that provide relative displacement information of the encoder member.

Abstract: An encoder is provided in which the absolute angle can be detected with high accuracy even when the irradiated position of light to be detected with respect to a scale is displaced from a reference, and a photodetecting device for an encoder used for such an encoder. In the encoder 1, by passing light to be detected through a straight-line light transmitting portion 17, a bright portion 19 to which the light to be detected is irradiated is formed in an area of a scale plate 11 containing mutually separate parts of arranged lines L1 and L2 and also a dark portion 20 to which no light to be detected is irradiated is formed in the other area.

Abstract: This invention relates to a position transmitter for the acquisition of the position of a shaft, rotatable about an axis of rotation, with a first optical sensor arrangement for the acquisition of the single-turn position of the shaft, and a second optical sensor arrangement for the acquisition of the multi-turn position of the shaft.

Abstract: This invention relates to a position transmitter for the acquisition of the position of a shaft, rotatable about an axis of rotation, comprising an optical sensor arrangement with a plurality of sensor elements, in which the plurality of sensor elements are provided for the acquisition of the single-turn position of the shaft, and whereby part of the plurality of sensor elements is provided for the acquisition, in particular for the gearless acquisition, of the multi-turn position of the shaft.

Abstract: An encoder position signal processing system comprises an analog encoder reader and a codewheel. The codewheel possesses an optical track that modulates the quadrature encoder signal amplitude in order to generate an amplitude change (home pulse) once per revolution of the codewheel. The analog encoder reader outputs a quadrature signal comprised of sine and cosine signals. The quadrature signal is converted to a magnitude signal that is sampled in order to generate a rate of change (ROC) signal, which increases the signal-to-noise ratio. An algorithm using the characteristic shape of the ROC home pulse signal can then be applied to the ROC signal to increases robustness of detecting the home pulse.

Abstract: A position transducer system is disclosed for a limited rotation motor that includes an illumination source that directs illumination toward an illumination reflector that rotates with a rotor of the limited rotation motor, and a plurality of detector areas adjacent the illumination source for receiving modulated reflected illumination from the illumination reflector.

Abstract: An optical encoder includes a rotation disc, an annular slit, a light source, an absolute-value-related detecting unit, and a signal processing device. The annular slit includes a first annular slit and a second annular slit which are decentered in a mutually different direction. The light source is configured to irradiate light on the annular slit. The absolute-value-related detecting unit is configured to detect transmitted light or reflected light irradiated from the light source and transmitted or reflected at the annular slit to output a detected signal. The absolute-value-related detecting unit includes a first detecting unit corresponding to the first annular slit and a second detecting unit corresponding to the second annular slit. The signal processing device is configured to detect an absolute rotational angle of the rotation disc based on the detected signal output from the absolute-value-related detecting unit.

Abstract: The invention relates to an information carrier (10), having a metal layer (40) with at least one track (14) in which marks (20) are disposed, which can be detected by means of light of a central wavelength (?) which is emitted by a light source (30) and which is incident upon the information carrier (10) at an angle (?i), and from which the position of the information carrier (10) can be derived, wherein the marks (20) are formed by areas (25) which are structured at least by first structures (22) of a lattice period (?) which are disposed on the back side (40b) of the metal layer (40) and/or on the front side (40a) of the metal layer (40), and wherein the lattice period (?) of the first structures (22) satisfies the equation ?=?/(np*?sin(?i)) or ?=?/(np*+sin(?i)), wherein ? is the central wavelength of the used light, ?i is the angle at which the light of the light source (30) is incident upon the information carrier (10) and np* is the effective index of a plasmon mode along the metal layer (40).

Abstract: A position-measuring device for generating a reference-pulse signal at at least one reference position includes a scanning unit and also a reflection-measuring graduation displaceable relative thereto in at least one measuring direction. The scanning unit for generating the reference-pulse signal includes a plurality of optical elements, including at least one imaging optics as well as at least two diaphragm structures, which are disposed in a diaphragm plane and have a plurality of diaphragm openings in each case. Furthermore, a light source as well as at least two detector elements are assigned to the scanning unit. The reflection-measuring graduation has a reference marking at the at least one reference position. It includes at least one set of first structure elements, which is arranged in the plane of the reflection-measuring graduation, perpendicular to the measuring direction, periodically at a first transversal periodicity.

Abstract: A scale and a position-measuring device include the shifting of reference markings in graduation tracks, offset transversely with respect to the measuring direction, by fractions of the interval of the reference markings within a graduation track. It is thus possible to eliminate, or at least to markedly reduce, negative effects of the disturbance of the periodicity of a graduation track by the reference markings.

Abstract: In one embodiment of the present invention, a rotary encoding switch is disclosed such as used in the function setting for relays or similar. In one embodiment, a particularly secure function setting for relays or similar may be achieved by means of a rotary encoding switch with a number of switch stages with separations between the switch stages which are not constant.

Abstract: A system and method for monitoring the rotation of a generator rotor and calculating a power angle using an optical rotor displacement monitor. The monitor uses a light beam directed toward the rotor to detect a marking thereon, and generates an electrical pulse when the marking is detected. The time between the pulse and a reference point (such as a zero crossing) of the signal waveform from the terminals of the generator is used to calculate the power angle of the generator. The system is adaptive in that it can account for new markings on the rotor. The system may be connected to a network so that power angles from various generators on the electrical network may be compared. The system may further be connected to a common time source such that a time stamp may be applied to the power angles from various generators, allowing for more accurate comparison of the power angles.

Abstract: An encoder device includes first through fourth photodiodes each having a rhombus shape and a length of X1 in an X direction, the photodiodes being disposed adjacent to each other in the X direction such that a line passing through a pair of opposing vertices of the rhombus shape of each of the photodiodes is parallel to an X axis; a slit member that includes light transmitting sections and light shielding sections alternately arranged, and is movable in the X direction, each of the light transmitting and shielding sections having a length of 2×X1 in the X direction; and a logic circuit that generates first and second detection signals from output signals of the photodiodes that have received lights passing through the light transmitting sections, a phase of the second detection signal being shifted by a ¼ period of the first detection signal relative to the first detection signal.

Abstract: An optical encoder. The encoder includes a coding element, an emitter, and a detector. The coding element has a track with a track pattern. The track pattern includes a plurality of optically distinguishable sections, which include a plurality of position sections and an index section. The emitter generates a light signal incident on the track of the coding element. The detector includes a combined position and index photodetector array. The combined position and index photodetector array includes a plurality of position photodetectors and an index photodetector. Embodiments of this type of optical encoder implement position and index sections in a single track on the coding element.

Abstract: A photodetector group includes a plurality of photodetector elements which are arranged one-dimensionally in a direction of movement of a scale. An optical encoder includes a differential signal calculating member which calculates a first differential signal of an output signal from one photodetector element and an output signal from other photodetector element, and a gate signal forming member which generates a gate signal which includes an area of zero crossing by the first differential signal, near a position where light emitted from a light source is incident on the photodetector group upon passing through a reference position pattern formed on a scale. The optical encoder outputs a reference position signal based on a point of zero crossing of the first differential signal and the gate signal.

Abstract: A mark detector to detect a plurality of marks which are arranged in a predetermined cycle on a moving member, such as a photo conductor belt, a transfer belt, a paper conveyance belt, a photo conductor drum, a transfer drum, etc. especially in an image forming apparatus, has an optical head including a light source to irradiate a light beam, a beam shaping device to shape the light beam, and a photo acceptor to accept light from the marks. Light beams on the marks from the light source have different positions shifted within a half mark cycle of each other on the marks. This increases accuracy and stability of controlling a motion of the moving member.

Abstract: An optical encoder includes an optical encoder pattern of alternating light elements and dark elements, and an optical unit, including an optical emitter providing light to the encoder pattern, and an optical sensor including a photo-detector receiving the light from the optical encoder pattern and in response thereto outputting a sinusoidal signal indicating relative movement between the optical sensor and the encoder pattern. In one embodiment, the photo-detector has a diamond shape, a modified-diamond shape, or an hourglass shape. In another embodiment, at least one of the light elements and the dark elements of the optical encoder pattern has a diamond shape, a modified-diamond shape, or an hourglass shape.

Abstract: An apparatus (100) for detecting rotational angle of a rotational element (110), includes a light emitting element (1) and an image detecting element (3). The light emitting element is disposed on the rotational element to emit light. The image detecting element has a plurality of reception zones (31, 32 . . . N) for receiving the light emitted. Each of the reception zones corresponds to an angular section of the rotational element.

Abstract: An angle-measuring system comprising at least one transmitter provided with a number of complementary signal-generating elements disposed in pairs and creating a pattern of signals. The elements create a reference mark irregularly configured at least at one spot. A device for acquiring the signals and an evaluation unit are also part of the angle-measuring system. The device is provided with at least one first sensor and one second sensor.

Abstract: Systems and methods are disclosed for providing position measurement information. For example, in accordance with one embodiment of the present invention, a multiple-pitch grating is disclosed which is adapted to receive one or more laser beams and provide an output laser beam encoded with position information of the grating.

Abstract: An angular offset sensing device includes an optical encoder having a light generating element and a light sensor. An armature includes a reflective surface having a generally semicircular shape and a spectrum of color disposed thereon varying from a first end of the surface to a second end of the surface. A housing encloses both the optical encoder and the armature and rotationally supports the armature. An electrical voltage is generated when light from the light generating element is reflected back to the sensor from the reflective surface. The voltage is proportional to a wavelength of the reflected light and is indicative of an angular rotation of the armature relative to the optical encoder. The voltage is corrected for linearity and used for example to signal a vehicle transfer case shift.

Abstract: An angular offset sensing device includes an optical encoder having a light generating element and a light sensor. An armature includes a reflective surface having a generally semicircular shape and a spectrum of color disposed thereon varying from a first end of the surface to a second end of the surface. A housing encloses both the optical encoder and the armature and rotationally supports the armature. An electrical voltage is generated when light from the light generating element is reflected back to the sensor from the reflective surface. The voltage is proportional to a wavelength of the reflected light and is indicative of an angular rotation of the armature relative to the optical encoder. The voltage is corrected for linearity and used for example to signal a vehicle transfer case shift.

Abstract: An angle absolute encoder comprises an encoded code rod that has code marks, such as pairs of fine code lines and coarse code lines. Light is reflected from or transmitted through the code marks and detected by a light detector to determine absolute angle position.

Abstract: An encoder and related methods for use in a printing device indexing system are provided. In some embodiments, the system comprises a feedroller or other component configured to index media through a printing device, and an encoder disk is coupled to the feedroller. In these embodiments, the system includes a reflective optical detector having a transmitter and a receiver provided adjacent a first surface of the encoder disk, the reflective optical detector being configured to detect the passage of the home position mark as the encoder disk rotates by the reflection of radiation off of the first surface. Also provided in some embodiments are methods for setting a counter to correspond with the home position of a rotatable element by utilizing threshold signal levels.

Abstract: A rotation angle detecting device includes a housing which is constituted by a combination of a case and a cover; a resistance board; a code wheel; a slider rotating plate; a slider; a circuit board; signal detecting elements; and a gear which transmits the rotation of the code wheel at a predetermined speed reduction ratio to the slider rotating plate, which are enclosed in the housing. Circular pin insertion holes are formed in positions where the code wheel, the case, and the cover face each other, respectively. A pin insertion hole having a circular-arc shape is formed in the slider rotating plate.

Abstract: A steering angle sensor assembly is for use with a vehicle having a rotatable steering mechanism. The assembly includes a first rotational indexing member operably couplable to the steering mechanism for rotation therewith. The steering mechanism and the first indexing member are each rotatable through a rotational range including a plurality of revolutions. The first indexing member defines a first rotational axis. A plurality of indexing elements are disposed on the first indexing member and circumscribe the first rotational axis. A first sensing device is positioned to sense the plurality of indexing elements as the first indexing member rotates. The first sensing device outputs a first signal representative of a rotational position of the first rotational indexing member within one of the revolutions. A second rotational indexing member defines a second rotational axis. A reduction gear mechanism operably couples the first and second indexing members.

Abstract: Systems and methods are disclosed for providing position measurement information. For example, in accordance with one embodiment of the present invention, a multiple-pitch grating is employed to receive one or more laser beams and provide an output laser beam encoded with position information of the grating.

Abstract: The present invention relates to a method for determining a home position by means of a home position mark on a special microfluidic device type used in a microfluidic system. The method for determining a home position by means of a home position mark on a microfluidic device used in a microfluidic system comprising at least one programmable controller having storage means, a position device being able to communicate with the controller, and a home position mark detector connected to said controller, wherein said method comprises the following steps: scanning a disc for mark edges; rejecting false home mark(s) and identifying a correct home position mark; and determining a home position by use of mark edges of the correct home position mark identified in the previous step. The present invention also relates to a microfluidic system and a computer program product and a computer program product on a computer usable medium.

Abstract: A system for accurately sensing/determining the position of an uniformly rotating shaft characterized in using a single marker in tandem with a high frequency signal, said system comprising a shaft mounted with a disc having a single marker, an opto-electronic device placed in front of the disc for generating a “marker signal” for every rotation of the disc, a means for producing a high frequency signal for sampling/slicing/slotting the time period between two consecutive marker signals, input terminals of a gating mechanism being connected to the opto-electronic device and the high frequency signal generator and an output terminal being connected to a counter such that the gating mechanism allows the high frequency signal to pass to the counter and said counter being configured for counting the number of pulses in the high frequency signal, a D/A converter connected to an output of the counter for converting the number of pulses counted into an analog signal and optionally, a display mechanism for displaying

Abstract: Disclosed is an apparatus for counting the rotation frequency of a numeral wheel of a meter to be used for a remote metering system. A light reflection tape is coated on one of low placed numeral wheels. A light sensor unit has an opaque case formed with first and second holes in which an infrared ray emitter and an infrared ray sensor are located, respectively. The light sensor unit is fixedly mounted on the ceiling of a rectangular shaped housing which is detachably coupled with a meter to cover the front of the meter. A portion of the housing over numeral wheels and a front plate of the meter is transparent. The transparent portion of the housing has an infrared ray rejection function to prevent infrared rays from entering into the housing. In place of employing such housing, a light shield may be used to shield a space between the light sensor unit and the light reflection tape coated numeral wheel from outer light.

Abstract: A rotational phase difference detecting system, a method that is capable of very accurately detecting a rotational phase difference between a plurality of rotating bodies, a machine operating-state monitoring system, and a method employing the rotational phase difference detecting system. The detecting system has a first rotating body with a first mark, a second rotating body with a second mark, a mark sensor for detecting the first mark, a first camera for imaging the second mark when the mark sensor detects the first mark, and a display section for displaying the second mark imaged by the first camera. The rotational phase difference is detected from a position of an image of the second mark displayed on the display section and is thus detected very accurately with a simple construction comprising the mark sensor, the first camera, and the display section.

Abstract: The invention involves a marked plate for a rotational angle sensor element for rotating structural parts, with many angle marks provided preferably oriented radially to the rotational axis and preferably arranged in the form of a collar arranged concentrically to the rotational axis and with at least one reference mark, which is formed by an angle mark that deviates in its modulating properties and thus is integrated in the collar of the angle marks. An angle sensor element system for rotating structural parts includes a marked plate that can be coupled to the rotating structural part and that merely has a collar of angle marks with integrated reference marks and a fixed scanning unit for it, including at least one transmitter of electromagnetic radiation and at least one receiver for the radiation modulated by the marked plate, as well as mechanisms for connection to an evaluation unit.

Abstract: A two-axis ball-based cursor control apparatus is provided, which includes a housing; a spherical ball contained partially within the housing; two rotors in contact with the spherical ball and two corresponding axles; two screw devices associated with each rotor-axle pair, each screw device having a continuous helical thread; a plurality of light sensors, each associated with a screw device; and a means for processing the signal from the light sensors. When the spherical ball is rotated by the user, its motion about each axis of rotation is translated to one of the screw devices by means of the corresponding rotor-axle pair. The rotation of the screw devices causes the helical thread on each to momentarily interrupt the light beam generated by each sensor at least once during each revolution of the screw device, thereby generating a signal which is translated into two-dimensional motion of a cursor on an electronic display screen.