WO2000077472A1 - Detecteur de position de code a enchainement - Google Patents

Detecteur de position de code a enchainement Download PDF

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Publication number
WO2000077472A1
WO2000077472A1 PCT/US2000/016370 US0016370W WO0077472A1 WO 2000077472 A1 WO2000077472 A1 WO 2000077472A1 US 0016370 W US0016370 W US 0016370W WO 0077472 A1 WO0077472 A1 WO 0077472A1
Authority
WO
WIPO (PCT)
Prior art keywords
scale
detector
bits
mark
array
Prior art date
Application number
PCT/US2000/016370
Other languages
English (en)
Inventor
Richard J. Norcross
David P. Engvall
W. Robert Bunch
Original Assignee
Snorkel International, Inc.
United States Of America As Represented By The Secretary Of Commerce, National Institute Of Standards And Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Snorkel International, Inc., United States Of America As Represented By The Secretary Of Commerce, National Institute Of Standards And Technology filed Critical Snorkel International, Inc.
Priority to AU57376/00A priority Critical patent/AU5737600A/en
Priority to EP00942804A priority patent/EP1192412A4/fr
Publication of WO2000077472A1 publication Critical patent/WO2000077472A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/20—Other details, e.g. assembly with regulating devices
    • F15B15/28—Means for indicating the position, e.g. end of stroke
    • F15B15/2815—Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
    • F15B15/2846—Position sensing, i.e. means for continuous measurement of position, e.g. LVDT using detection of markings, e.g. markings on the piston rod
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
    • G01D5/249—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains using pulse code
    • G01D5/2492—Pulse stream
    • G01D5/2495—Pseudo-random code
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/347—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using displacement encoding scales
    • G01D5/34746—Linear encoders
    • G01D5/34753—Carriages; Driving or coupling means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/347—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using displacement encoding scales
    • G01D5/34776—Absolute encoders with analogue or digital scales
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/22—Analogue/digital converters pattern-reading type
    • H03M1/24—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip
    • H03M1/28—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding
    • H03M1/282—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding of the pattern-shifting type, e.g. pseudo-random chain code

Definitions

  • the invention generally relates to an apparatus for measuring the position of a moving member relative to a stationary member and, in particular, a scale on a rod of a linear motion cylinder (having a rod, housing, gland and driving element such as a piston or rotor) and a detector on the cylinder housing for detecting the scale to indicate the position of the rod relative to the housing, thus detecting the length of the cylinder.
  • a linear motion cylinder having a rod, housing, gland and driving element such as a piston or rotor
  • detector on the cylinder housing for detecting the scale to indicate the position of the rod relative to the housing, thus detecting the length of the cylinder.
  • the apparatus of the invention has several advantages over the prior art including instant position detection, increased resolution, inherent redundancy, low maintenance, and vibration tolerance.
  • the apparatus of the invention addresses many of the hydraulic cylinder position measurement problems to provide an excellent solution in that area as well as in any area where position detection is required.
  • the general approach can be applied to other position measuring problems where one element moves along another.
  • the invention measures the position of the cylinder rod by observing a scale having sequences of coded marks on the cylinder rod.
  • the cylinder rod presents a rigid base for scales and is thus resistant to mechanical vibration.
  • the scales are inexpensively applied to the cylinder rod through such techniques as photo engraving or laser marking.
  • the detector for detecting the sequences of coded marks comprises an array of detectors such as an electronic camera. The detector preferably takes multiple readings of the sequence so that the resultant information is resistant to sporadic errors. From a manufacturing standpoint, the detectors are structured to be replicated on a consistent basis to enhance system reliability.
  • the invention employs a stationary detector on the cylinder housing and a scale (preferably illuminated) having a code marked on the cylinder rod which code does not repeat itself within a desired range.
  • the scale may use a chain code to provide an absolute position while viewing a minimum length of the scale.
  • the detector uses the two-dimensional array of detector elements to detect the image of the scale.
  • a lens or other focusing device may be used to transfer the image to the detector.
  • the multiple detector elements provide multiple signals which, when evaluated, provide redundancy, error tolerance and improved resolution.
  • the invention comprises a device for sensing the position and velocity of a movable member which moves along an axis relative to a stationary member.
  • a scale encompassing a nonrepeating code is on the movable member aligned substantially along the axis of movement.
  • a detector is fixed to the stationary member and positioned to sense a portion of the scale. The detector generates a plurality of signals, each signal indicative of the portion of the scale sensed by the detector.
  • a controller determines the position of the movable member relative to the stationary member as a function of the signals.
  • Figure 1 is a side perspective view of a cylinder housing having a detector thereon and a cylinder rod having a scale thereon according to the invention.
  • Figure 1A is a schematic side view of one preferred embodiment of an aerial work platform machine according to the invention.
  • Figure 2 is a block diagram of one preferred embodiment according to the invention of an imager and related components for processing a data signal provided by the imager.
  • Figure 3 illustrates one preferred embodiment according to the invention of a scale having an 8-bit chain code.
  • FIG. 4 illustrates other preferred embodiments of scale codes according to the invention.
  • Figure 5 is a schematic illustration of one preferred embodiment according to the invention of a zero clearance detector.
  • Figure 6 is a schematic illustration of one preferred embodiment according to the invention of a detector having a pin hole lens .
  • Figure 7 is a plan view of the front of the detector illustrating the pixel arrangement.
  • Figure 8A is a waveform diagram of one preferred embodiment according to the invention wherein the scale marks are perpendicular to the axis of movement and the detector is read along the length of the scale marks perpendicular to the axis of movement .
  • Figure 8B is a waveform diagram of one preferred embodiment according to the invention wherein the scale marks are perpendicular to the axis of movement and the detector is read along the direction of the axis of movement .
  • Figure 9 illustrates various waveforms relating to the detector output of one row of detectors .
  • Figure 10 is an illustration of interpolation according to one preferred embodiment of the invention.
  • Figure 11 illustrates a partial side view of a cylinder position detector with self focusing lens arrays.
  • FIG. 1 a partial schematic perspective view of one preferred embodiment of a linear motion cylinder (hydraulic, pneumatic or electrical) according to the invention for use as a position sensor is illustrated.
  • a cylinder gland nut 10 guides a rod 11 with a scale 12 thereon consisting of a pseudo-random series of bits known as a chain code.
  • the scale 12 is aligned with the axial motion 13 of the rod 11.
  • a detector 14 is mounted in the gland nut of the cylinder over a portion of the scale 12 on a circuit board 15. The detector 14 generates a signal which indicates the position of the rod from the observed portion of the scale 12 and the circuit board 15 periodically communicates the position data along a communications medium (e.g., wires) 16.
  • a communications medium e.g., wires
  • FIG. 1A a schematic side view of one preferred embodiment of machine such as an aerial work platform 100 according to the invention is illustrated. Although the invention is not limited to aerial work platforms, articulated booms and the like, Figure 1A shows such a machine for the purposes of illustration only. Those skilled in the art will recognize that the invention may be used in many different applications where position or time based derivatives or other position related parameters need to be monitored or sensed.
  • the machine illustrated in schematic form in Figure 1A includes a base 102 supported by a plurality of wheels 104.
  • An extendable boom 106 is supported by the base 102 and has a movable section 108 which is movable relative to a reference section 110.
  • the moveable section 108 is adapted to support a work platform 112.
  • a cylinder 114 drives a movable section such as a cylinder rod 116 along an axis 118.
  • the cylinder 114 is hinged to the reference section 110 whereas the cylinder rod 116 is hinged to the movable section 108.
  • the cylinder 114 may be hinged to the movable section 108 and that the cylinder rod 116 may be hinged to the reference section 110.
  • the movable section 108 of the boom is rotated about the hinge pin which connects it to the reference section 110.
  • movement of the cylinder rod 116 along the axis 118 which movement by the cylinder rod is relative to the cylinder 114 causes rotational movement of the movable section 118 relative to the reference section 110.
  • a scale 120 is engraved, etched or marked on to the cylinder rod 116 and runs along the axis of the cylinder rod which is coincident with axis 118.
  • the portion of the scale that appears on the cylinder rod 116 has a nonrepeating code although the code in general may have a repetition rate which is greater than the length of the amount of scale that appears on the cylinder rod 116.
  • a two-dimensional detector 122 is affixed to the cylinder 114 so that it is stationary relative to the cylinder rod 116.
  • the detector 122 is positioned to sense a portion of the scale 120 on the cylinder rod 116.
  • the detector is connected to a hydraulic controller 124 which controls the operation of the cylinder 114.
  • the detector 122 is connected by a wire harness 126 to the controller 124.
  • the detector 122 generates a plurality of signals, each signal indicative of the portion of the scale being sensed by the detector.
  • the controller determines the position of the cylinder rod 116 relative to the cylinder 114 as a function of the signals provided to it by the detector 122.
  • Figure 2 is a block diagram of one preferred embodiment according to the invention of the components of a controller for processing the signal provided by detector 122 shown in Figure 1.
  • the detector is an image detector such as a CCD or CMOS camera 202 providing a data signal via the harness 204 which connects the detector 202 to a controller 206.
  • the controller 206 includes an analog to digital (A/D) converter 208 for converting the analog data signal provided via harness 204 into a digital signal supplied to a digital processor 210 for processing.
  • the processor 210 may refer to a look up table 212 to assist in the analysis and recognition of the portion of the code being sensed.
  • the scale according to the invention is a pseudo-random collection of marks and spaces commonly known as a chain code.
  • the imager 202 constitutes a detector array providing a two-dimensional package of detector elements and can be implemented by an electronic camera.
  • the scale is a physical representation of the code.
  • the code is represented by a series of marks and spaces (with gaps therebetween) .
  • the marks and spaces have 25 mils center-to-center spacing with each mark and space being about 18 mils wide and each gap between the marks being about 7 mils wide.
  • the code is represented by a binary number.
  • the portion of the scale being read is an area on the cylinder rod while the portion of the code is a number sequence.
  • the marks and spaces on the cylinder rod form the chain code.
  • an N-bit chain code is a pseudo-random sequence of bits arranged such that any N-bit sub-sequence is unique within the total sequence which appears on the cylinder rod 116.
  • the chain code itself may be repeating, the repetition period is greater in length than the portion of code of interest on the cylinder rod 116.
  • the absolute position of the cylinder rod relative to the cylinder can be determined such as by a look up table or by the product of the mark spacing and the position of the sub-sequence in the whole sequence.
  • the chain code may be any size.
  • the sequence "10” is a one bit chain code sequence.
  • "00110" is a two bit chain code.
  • the scale illustrated in Figure 3 is an 8 bit code with the left most value being 10000101 (133) and the next value adjacent to it being 00001011 (11) .
  • the number of bits in a chain code can be any number up to 2 N + N-l yielding up to 2 N unique N-bit subsequences.
  • a chain code covers a distance up to the product of the bit spacing and the number of bits. In general, a 24 bit code constitutes one preferred embodiment.
  • the chain code provides a minimum number of marks in every N bit sequence.
  • a simple computer program can build the scale by computing the value by left shifting the previous value and checking a flag that indicates whether the value is in use. If the value is already in use, the program changes the first bit and checks the new value. If that value is also in use, the program backtracks in the scale until the bit change generates an unused value. A flag for the new value is set and the cycle repeats. To ensure that the values have a minimum number of marks (M) , the flags of the values with fewer than M "1" bits may be preset. A minimum number of spaces can also be ensured in a similar fashion. Those skilled in the art will recognize that other algorithms may be used to generate such codes. One advantage of the chain code is that it minimizes the number of bits that must be observed to determine a unique position.
  • the representations include a bar code 402, a line bar code 404, a solid binary bar code 406 and a gapped binary code 408.
  • the bar code 402 uses alternating light and dark areas having a thickness which determines the indicated value (generally thicker for a 1 and thinner for a 0) .
  • the line bar code 404 uses a sequence of evenly spaced long and short lines wherein the long line represents a "1" while the short line represents "0.”
  • the solid binary bar code 406 uses marks that are as wide as the bit spacing.
  • a gapped binary code 408 may be preferred because the mark width is less than the bit width.
  • other preferred embodiments include a scale comprising evenly spaced bits of marks or spaces on the movable cylinder rod and where the mark width is less than the bit spacing; or evenly spaced marks wherein the length of the mark defines its bit value; or unevenly spaced bits of marks or spaces on the movable cylinder rod wherein the width of the mark or the width of the space defines its bit value.
  • FIG 5 illustrates one preferred embodiment of an apparatus according to the invention referred to as a zero clearance detector employed to detect the position of a cylinder rod 502 driven by a hydraulic cylinder 518 (see also reference character 114 in Figure 1) .
  • cylinder rods 502 are chrome plated so that chrome forms a hard, porous surface that absorbs minute amounts of oil while inside the hydraulic cylinder.
  • the pressure on the chrome falls and the absorbed oil flows out of the chrome and lubricates the seal between the gland and the rod.
  • One advantage of the scales according to the invention is that such scales provide spaces and provide gaps between the marks . These spaces and gaps present chrome which is available to lubricate the seal .
  • any detector or sensor may be used to read the scale on cylinder rod 502.
  • a contact detector may be used in which case the scale is read directly by contact so that an image of the scale is not transferred to the detector and the image does not need to be focused.
  • the detector comprises an optical detector such as a CCD or CMOS detector, it is preferable to transfer an image of the scale on the detector to enhance the accuracy of the apparatus according to the invention.
  • the detector may also be other sensing devices such as a CMOS optical detector.
  • one preferred focusing device may be a block of densely packed and commonly aligned optical fibers known as an optical conduit 504.
  • the optical conduit 504 is interposed between the cylinder rod 502 and a detector 506 to eliminate the gap therebetween.
  • the optical conduit 504 rides on the surface of the cylinder rod 502, either within or immediately above the oil film. Since condensation, dust and oil vapors have the potential to collect in the gap and interfere with the viewing of the scale by the detector 506, gap elimination improves the reliability of the invention.
  • an illumination source 510 may be positioned within the gap around the periphery of the optical conduit 504.
  • LEDs may be positioned on either end or around the periphery of the optical conduit to emit light which is transmitted by the optical conduit 504, reflected by the scale 508 and detected by the detector 506.
  • the detector 506 generates signals which are provided to electronics 512 which signals are then transmitted to a controller via a communications connector 514 such as an IEEE transducer independent interface or bus.
  • a detector housing 516 is supported and fixed on the cylinder 518 so that it is fixed relative to the housing of the cylinder and the rod 502 moves relative to the housing along the axis 520.
  • the housing 516 supports the detector 506 and optical conduit 504 as well as the illumination source 510.
  • the electronics 512 are enclosed within the housing 516.
  • the communications connector 514 is connected to the controller via a harness (not shown in Figure 5; see Figure 1, reference character 126) .
  • Other optical techniques may be used to focus an image of the scale 508 on the detector 506.
  • a pin hole lens 602 may be positioned between the cylinder rod 502 and the detector 506 as shown in Figure 6.
  • pin hole lenses may tend to be less expensive than the optical conduit 504, such pin hole lenses may require additional illumination as compared to the illumination required by an optical conduit 504.
  • Pin hole lens applications may be particularly useful in relatively clean environments.
  • Another optical focusing technique which is contemplated includes the use of a conventional optic lens (not shown) positioned between the cylinder rod 502 and detector 506 in place of pin hole lens 602. While a conventional optical lens may actually require less illumination to transform the image than the illumination required by an optical conduit 504, the lens itself must be selected to provide an undistorted image at such a short standoff. In addition, some lens may be spaced 11 from both the surface of the cylinder rod 506 which carries the code 508 and the surface of the detector 506 thereby defining cavities that can become contaminated.
  • the detectors 506 include high density detector arrays as shown in Figure 7 having a dimension of at least KxL elements.
  • the detector has K columns Cl-CK of elements defining its width (horizontally, along the axis 520) where K is much greater than the N bits of the code mark 700 preferably by an order of about 5 or more.
  • the detector also has and L rows Rl-RL of elements defining its length (vertically, perpendicular to the axis 500) where L is equal to or greater than one.
  • the detector array is sized and positioned to simultaneously detect N+1 or more bits.
  • the image is processed by the electronics 512 (Fig. 5) and the final values are presented on a communications medium (e.g., CAN, RS-232, 4-20mA) .
  • a communications medium e.g., CAN, RS-232, 4-20mA
  • the detector 506 may read the scale along the length of each of the marks of the code (vertically as shown in Figure 8A) or along the width of the marks and along the travel axis 520 (horizontally as shown in Figure 8B) .
  • Figure 8A illustrates the waveforms that would be generated by reading the scale along the length of the marks. This type of reading allows K signals to be easily integrated. Such K integration, performed by the digital processor 210, filters out most noise and leaves K values to be interpreted. The Appendix describes one preferred embodiment for processing such signals.
  • Figure 9 illustrates one such waveform analog data signal 906 from imager 202, which is generated by taking the analog output 902 from a CMOS imager viewing the scale and subtracting background noise 904.
  • the code 508 preferably comprises a chain code having marks 700.
  • Each mark has a length oriented substantially perpendicular to the axis 520 although marks having other orientation such as diagonal marks are contemplated.
  • the imager 202 constitutes an array forming L rows of elements (pixels) along the length L of each mark and forming K columns of elements along a width of the marks. The elements are read vertically. The elements in the first column are read successively to produce a signal SCI. The elements of adjacent columns read successively to generate a plurality of signals SC2 , SC3, ... , SCK.
  • the detectors may also read the scale along axis 520 which would be along the width of the marks as shown in Figure 8B. Each K set of pixels produces a reading of the entire scale. These readings may be compared and combined to remove spurious noise.
  • the code 508 preferably comprises an N-bit chain code having marks 800.
  • Each mark has a length oriented substantially perpendicular to the axis 520.
  • the imager 202 constitutes an array forming L rows of elements (pixels) along the length of each mark and forming K columns of elements observing N+ bits of the scale. The elements are read horizontally. The elements in the first row are read successively to produce a signal SRI. The elements of adjacent rows read successively to generate a plurality of signals SR2 , SR3 , ... , SRL.
  • Figure 8B shows a window of N + 1 bits for detecting an N-bit code.
  • the detector resolution may in fact be finer than the size of the pixel.
  • the centers Cl-CL are interpolated across the middle of the detector as illustrated in Figure 10.
  • the intersection I of the interpolation in the detector middle is the actual position of the scale relative to the detector.
  • the detector data is interpreted to provide the bit sub-sequence of the code that is under the detector and the position of the center of one or more marks.
  • the mark centers provide a position resolution in excess of the resolution of the scale. The higher resolution allows small changes in position to be used to compute the motion velocity from sequential sensor readings.
  • Figure 11 illustrates a cylinder position detector with self focusing lens arrays according to the invention.
  • two scales A and B on the cylinder rod 950 are illuminated by a light source 952 projecting light at an illumination angle 954 sufficient to illuminate both scales A and B.
  • Two self focusing lens arrays 956, 958 are positioned between scales A and B and an imaging array 960, respectively.
  • the arrays have a view angle 962, 964 for sensing the scales and project the sensed images 966, 968 of scales A and B onto the imaging array 960.
  • a portion 970 of the imaging array 960 is unused.
  • the code comprises a group of two or more repeating codes, each code represented by one of the scales A or B.
  • the code of scale A has a different number of bits than the code of scale B, where the number of bits do not have a common denominator.
  • the codes are aligned with each other along the axis of motion, the combination of N bits from each repeating code does not repeat for the length of the scale.
  • the discussions above are with regard to position resolution but not with regard to position accuracy. While the resolution of the detector 506 is a function of the type of detector, the sensor's accuracy is a function of the scale. The sensor's accuracy may be improved when a look up table 212 is used for position conversion rather then the offset computation.
  • a look-up table produces independent values for each sub-sequence in the chain code and can be set up to compensate for inaccuracies. The table can also provide information on environmental effects such as temperature. Enhanced resolution and the possibility of enhanced accuracy are two advantages to the invention.
  • N marks constitute the portion of the scale being detected
  • N+1 marks are sensed.
  • N+2 or more marks may be sensed and used to detect two portions of the scale (e.g., 1 to N and 2 to N + 1 may be detected) to provide redundancy.
  • the portion of the scale being detected equals N+A 14 marks (where A is greater than or equal to one) and the portion of the scale being processed by the controller equals N marks within in the N+A marks being detected so that two or more different sets of N marks within the N+A marks are processed by the controller.
  • the L rows of pixels may be divided into J groups of rows so that interpretation of J subsets of L/J pixels each can also be used to provide velocity data in high speed applications.
  • Each of the J subsets of L detector elements would be activated at tightly controlled intervals.
  • the position sensed by the later subset detector elements will be offset from the earlier subset detector elements. This offset can be measured and the derivatives of the position calculated.
  • Absolute position detectors based on serial scales generally require movement prior to the identification of the initial position. Since the invention reads N+A bits of the chain code each cycle, the detector detects the absolute position prior to any motion. Determining the position prior to motion is important in motion control applications where the machine may start away from fixed points.
  • the invention takes a broad view of the scale; thus, while part of a mark or space may not be visible, the detector will have sufficient data to evaluate the condition of the scale and to distinguish the actual position.
  • the controller can also request maintenance when the system resolution degrades below a preset value.
  • the resolution of an absolute position detector with a serial scale is commonly a function of the scale.
  • very fine scale spacing is required. Since the distance covered by the detector is the product of the spacing and the number of bits in the scale, coverage (the scale's length) may have to be sacrificed to achieve reasonable resolution.
  • the manufacturing cost of the scale tends to increase as the spacing decreases.
  • the resolution is a function of the detector array. Thus, the spacing can be larger allowing for greater detector coverage and lower manufacturing costs then the current absolute position detectors.
  • the scale's coverage may be larger then the ability to manufacture the scale.
  • smaller scale segments would be assembled end to end.
  • the joints between the scale segments can be identified by a wider mark, such as a blank area between the scales or a joint mark such as a distinctive line (e.g., a diagonal) .
  • the joint mark would be identifiable as not part of the chain code.
  • the portion of the chain code immediately before or after the joint mark would identify the joint, e.g., if a dozen joints were in the scale, four bits would have to be unique on either side of the joint mark to identify the location. Since the invention scans the scale, the invention can detect and identify the joint without additional hardware.
  • the invention preferably uses gapped scales representing a code.
  • the code is applied to the rod to form a scale of marks and spaces.
  • the marks have a common length and align along the axis of motion 103.
  • the preferred embodiment of the invention uses gapped scales.
  • the gapped scale has a consistent bit spacing and a mark width smaller then the bit spacing that leaves a small amount of unmarked material between successive marks. This characteristic has advantages for the invention in general and the hydraulic cylinder application in particular.
  • the small gap between the marks simplifies their manufacture, ensures the mark widths are constant, and simplifies the computation of the center used for improved resolution.
  • the gap leaves unmodified chrome to perform the necessary lubrication of the cylinder gland.
  • the scale would be marked on the hydraulic cylinder rod's chromeplate through laser photo-absorption or similar process. Note that the initial chrome coating must be of high quality to maintain adequate corrosion resistance or a process can be applied after the marking to restore the corrosion resistance.
  • the gapped scale was developed for environments where the spacing between the scale and the detector could be rigidly controlled.
  • the scale may use a more traditional bar code approach to distinguish the "1" and "0" bits.
  • the bits could be based on mark length, such as used on mail envelopes, or based on thickness, such as used on product labels.
  • the detector would be sized to view either the longer line or N+ wide bits respectively.
  • one application for this invention is to measure the position of a cylinder rod 502 driven by a hydraulic cylinder 518.
  • the scale would be marked on cylinder rod 502 while the detector (e.g., Figures 5 and 6) would be mounted near or on the gland.
  • the scales would be marked directly on the cylinder rod's chrome plate through laser photo-absorption.
  • the scales can be etched on anodized aluminum to be rugged, low cost, and very flexible.
  • Position control of gantry cranes would, in particular, benefit from this invention.
  • Other applications would be to control drawbridges, canal locks, gantry cranes, tower cranes, elevators, conveyors, robotics or computer controlled painters.
  • High speed applications would include automobile shock absorbers.
  • the invention could provide the position and velocity necessary to monitor road and handling conditions and to allow automatic compensation.
  • the laboratory model used a miniature, monochrome CCD camera, a pin hole lens, and an acrylic mount.
  • the camera outputs NTSC (RS-117) video.
  • NTSC transmits two interlaced 242 line by 500 pixel frames 30 times per second, only one frame was used in the measurement .
  • the camera was mounted such that the horizontal camera lines were parallel to the chain code marks.
  • the pin hole lens was a simple 100 micron hole in thin aluminum.
  • An acrylic mount held the camera, the lens, and up to 16 ED's
  • the mount maintained suitable standoff to view 15+ bits of the chain code.
  • the mount had a cone shaped interior cavity with a light diffusing surface (i.e., the surface was lightly ruffed) . 12 LED's were set in the acrylic mount to illuminate the scale under the cone.
  • NTSC is an analog signal. The signal was heavily filtered through an RC circuit.
  • Thresh (Min - Max) * 4 / 50

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'invention concerne un détecteur de position destiné à détecter la position d'un élément mobile se déplaçant le long d'un axe par rapport à un élément fixe (11). Un code d'enchaînement non répétitif à n bits, intégré dans une échelle se trouvant sur l'élément mobile, se déplace le long dudit axe (13). Un détecteur (14) fixé à l'élément fixe (11) est disposé de façon à détecter une partie du code d'enchaînement. Le détecteur possède k éléments (k>>n) produisant une pluralité de signaux. Une unité de commande (10) détermine la position de l'élément mobile par rapport à l'élément fixe en fonction desdits signaux.
PCT/US2000/016370 1999-06-16 2000-06-14 Detecteur de position de code a enchainement WO2000077472A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU57376/00A AU5737600A (en) 1999-06-16 2000-06-14 Chain code position detector
EP00942804A EP1192412A4 (fr) 1999-06-16 2000-06-14 Detecteur de position de code a enchainement

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US13944799P 1999-06-16 1999-06-16
US60/139,447 1999-06-16

Publications (1)

Publication Number Publication Date
WO2000077472A1 true WO2000077472A1 (fr) 2000-12-21

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2000/016370 WO2000077472A1 (fr) 1999-06-16 2000-06-14 Detecteur de position de code a enchainement

Country Status (3)

Country Link
EP (1) EP1192412A4 (fr)
AU (1) AU5737600A (fr)
WO (1) WO2000077472A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002092153A3 (fr) * 2001-05-16 2003-10-16 Lilly Co Eli Appareil injecteur de medication avec ensemble d'entrainement qui facilite le rearmement
GB2537339A (en) * 2014-12-15 2016-10-19 Parker Hannifin Mfg Ltd A cylinder with position feedback sensor
WO2020149747A1 (fr) * 2019-01-18 2020-07-23 C6 Technologies As Capteur de position résistif
US10857304B2 (en) 2016-03-25 2020-12-08 Eli Lilly And Company Determination of a dose set and delivered in a medication delivery device
US11266788B2 (en) 2016-04-19 2022-03-08 Eli Lilly And Company Determination of a dose in a medication delivery device using two moving arrays with teeth and a sensor
US11452819B2 (en) 2016-12-15 2022-09-27 Eli Lilly And Company Medication delivery device with sensing system
US11471607B2 (en) 2016-08-12 2022-10-18 Eli Lilly And Company Dose sensing mechanism in a medication delivery device

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002092153A3 (fr) * 2001-05-16 2003-10-16 Lilly Co Eli Appareil injecteur de medication avec ensemble d'entrainement qui facilite le rearmement
US7195616B2 (en) 2001-05-16 2007-03-27 Eli Lilly And Company Medication injector apparatus with drive assembly that facilitates reset
US7704238B2 (en) 2001-05-16 2010-04-27 Eli Lilly And Company Medication injector apparatus with drive assembly that facilitates reset
EP2275158A3 (fr) * 2001-05-16 2011-10-19 Eli Lilly and Company Appareil injecteur de médication avec ensemble d'entraînement qui facilite le réarmement
US8672899B2 (en) 2001-05-16 2014-03-18 Eli Lilly And Company Medication injector apparatus with drive assembly that facilitates reset
US9220845B2 (en) 2001-05-16 2015-12-29 Eli Lilly And Company Medication injector apparatus with drive assembly that facilitates reset
GB2537339A (en) * 2014-12-15 2016-10-19 Parker Hannifin Mfg Ltd A cylinder with position feedback sensor
US10857304B2 (en) 2016-03-25 2020-12-08 Eli Lilly And Company Determination of a dose set and delivered in a medication delivery device
US11266788B2 (en) 2016-04-19 2022-03-08 Eli Lilly And Company Determination of a dose in a medication delivery device using two moving arrays with teeth and a sensor
US11471607B2 (en) 2016-08-12 2022-10-18 Eli Lilly And Company Dose sensing mechanism in a medication delivery device
US11452819B2 (en) 2016-12-15 2022-09-27 Eli Lilly And Company Medication delivery device with sensing system
WO2020149747A1 (fr) * 2019-01-18 2020-07-23 C6 Technologies As Capteur de position résistif

Also Published As

Publication number Publication date
EP1192412A1 (fr) 2002-04-03
EP1192412A4 (fr) 2003-05-14
AU5737600A (en) 2001-01-02

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