WO2003079555A2 - Codeur a marques de reference - Google Patents

Codeur a marques de reference Download PDF

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Publication number
WO2003079555A2
WO2003079555A2 PCT/GB2003/001087 GB0301087W WO03079555A2 WO 2003079555 A2 WO2003079555 A2 WO 2003079555A2 GB 0301087 W GB0301087 W GB 0301087W WO 03079555 A2 WO03079555 A2 WO 03079555A2
Authority
WO
WIPO (PCT)
Prior art keywords
scale
detector
reference marks
marks
readhead
Prior art date
Application number
PCT/GB2003/001087
Other languages
English (en)
Other versions
WO2003079555A3 (fr
Inventor
James Reynolds Henshaw
Michael Homer
David Roberts Mcmurtry
Original Assignee
Renishaw Plc
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 Renishaw Plc filed Critical Renishaw Plc
Priority to AU2003224235A priority Critical patent/AU2003224235A1/en
Publication of WO2003079555A2 publication Critical patent/WO2003079555A2/fr
Publication of WO2003079555A3 publication Critical patent/WO2003079555A3/fr

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
    • H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
    • H03M1/0675—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence using redundancy
    • H03M1/0678—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence using redundancy using additional components or elements, e.g. dummy components
    • 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
    • G01D5/245—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 a variable number of pulses in a train
    • G01D5/2454—Encoders incorporating incremental and absolute signals
    • G01D5/2455—Encoders incorporating incremental and absolute signals with incremental and absolute tracks on the same encoder
    • G01D5/2457—Incremental encoders having reference marks
    • 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
    • H03M1/30—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding incremental
    • H03M1/308—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding incremental with additional pattern means for determining the absolute position, e.g. reference marks

Definitions

  • This invention relates to encoders.
  • Encoders are used to measure the movement of one member relative to another, and typically comprise a scale on one member and a readhead on the other. As the readhead passes along the scale, it reacts to periodic marks on the scale in order to produce a periodic output, e.g. a train of pulses. The pulses are counted incrementally by an external counter in order to give an indication of the distance travelled.
  • one of the tracks may contain the periodic scale marks themselves, while another contains a reference mark or marks.
  • the reference mark indicates a datum position along the scale, which can be detected by a detector in the readhead. As the readhead passes over the reference mark, it produces a pulse used to reset the counter. This enables the counter to give an indication of absolute position relative to the reference mark. For example, when the encoder is first switched on, it is important that the counter should be reset by the reference mark, otherwise the position indication given will be arbitrary.
  • the present invention seeks to provide an arrangement for a reference mark and reference mark detector which is less sensitive to yaw misalignment.
  • the present invention provides an encoder comprising a scale and a readhead which is movable along the scale; the scale comprising a main scale track with a series of periodic scale marks extending along the scale, and two co-operating reference marks associated with a position along the scale and spaced laterally with respect to each other; the readhead including a reference mark detector or detectors for detection of said two reference marks; a combined output being produced from the detection of both said reference marks.
  • the combined reference mark signal can average the Abbe errors from the two reference marks, thereby reducing their effect.
  • the two reference marks are located laterally on opposite sides of the main scale track, so that their Abbe errors are equal and opposite and are substantially cancelled when the signals from the reference marks are combined.
  • Fig 1 is a schematic isometric view of part of a scale and a readhead of an encoder
  • Figs 2,3 and 4 are graphs of detector signals before and after combination
  • Figs 5, 6 and 7 are schematic isometric views of three modifications of the scale and readhead of Fig 1.
  • an optical scale 10 has a main scale track 12 with a series of periodically spaced scale marks extending in the longitudinal direction. Laterally on each side of the main scale track 12 are respective reference tracks 14,16.
  • the reference tracks 14,16 each contain one or more reference marks 18,20.
  • the reference marks 18,20 in this embodiment, comprise thin laterally extending substantially specularly reflective lines on a non-reflective background of the reference track.
  • a readhead is indicated generally at 22 in Fig 1.
  • the scale 10 and readhead 22 are fixed to respective relatively movable members, such that the readhead moves back and forth along the scale in the longitudinal direction indicated by arrow X.
  • a conventional optical detector 24 in the readhead interacts with the periodic marks of the scale track 12 and produces a pulse train to a counter (not shown) in the conventional manner, indicating the incremental distance travelled along the scale.
  • the readhead 22 includes two light emitters 26,28, located one on each side of the centre line of the scale. Preferably they are in the form of laterally extending lines, as shown. Each line light emitter 26,28 directs light to a respective reference mark 18,20. The reflective reference marks 18,20 then reflect this light towards a central split detector 30.
  • the split detector has two photosensitive regions 30A, 30B, each being elongate (similar to the line light emitters 26,28 and the reflective marks 18,20) and extending laterally, spaced in the longitudinal direction from each other.
  • the two halves 30A, 30B of the split detector 30 produce signals which are taken to a differential amplifier 32.
  • the output of this differential amplifier is indicative of the difference between the two signals, and is taken to a zero crossing detector 34 which provides an output pulse when the difference signal crosses zero. This is taken to the external counter (not shown) in order to reset it.
  • the differential amplifier 32 and zero crossing detector 34 may be provided within the readhead, or in a separate interface circuit between the readhead and the external counter.
  • the curve A in the upper graph shows the response of one half 30A of the split detector, as the readhead moves over the reference marks in the longitudinal direction. This is a notional response, indicating the signal resulting from only one of the reference marks and its corresponding line light emitter, isolated from the signal resulting from the other reference mark.
  • the curve B in Fig 2 indicates the corresponding response of the half 30B of the split detector, which of course is spaced from the curve A in the longitudinal direction X.
  • the lower graph in Fig 2 is a curve showing A-B, as output from the differential amplifier 32, and it will be understood that the zero crossing detector 34 produces its output pulse at the point 0 where the curve crosses the X axis.
  • Fig 3 shows the notional result if the system suffers from yaw misalignment (again considering the signal resulting from just one reference mark) .
  • a yaw error has the effect of shifting the reference signals slightly in the X direction, so that the pulse output by the zero crossing detector 34 no longer occurs at the point 0.
  • the output from the zero crossing detector 34 is insensitive to the yaw misalignment.
  • Fig 5 shows a modification of the arrangement shown in Fig 1.
  • a single line light emitter 40 is located centrally, in the position of the split detector 30 in Fig 1. This reflects light from the two reference marks 18,20 towards respective split detectors 42,44, located in place of the line light emitters 26,28 shown in Fig 1.
  • the signals from these two split detectors are combined electronically. Specifically, the signals from each of the A channels are summed in a summing circuit 46 and separately the signals from each of the B channels are summed in a summing circuit 48. The resulting combined signals are then taken to the differential amplifier 32 to provide the A-B signal as previously.
  • the summing circuits 46,48 may be provided within the readhead, or in a separate interface circuit between the readhead and the external counter.
  • the respective light source and split detector may be spaced laterally, as in Fig 6.
  • the light source and split detector may be spaced longitudinally, as in Fig 7. In the latter case, it will be appreciated that the light source and reference mark are located physically above the reference track 14 or 16 in which the reference mark concerned is provided.
  • the invention can also be applied to a transmissive optical scale, in which the reference tracks 14,16 are generally opaque, with transparent windows forming the reference marks 18,20.
  • the light sources are then located on the other side of the scale relative to the detectors.
  • the invention can also be applied to diffusely reflective reference marks, e.g. with suitable lens arrangements.
  • the reference marks do not need to be single lines as seen at 18 and 20. They could instead be, for example, chirped reference marks. Alternatively they could be autocorrelating marks in arrangements such as described in our International Patent Application No. PCT/GB02/00638.
  • a scale could have magnetic reference marks, one on each side of the main scale track.
  • the readhead then has respective magnetic detectors for the reference marks, again on either side of the main scale track, the signals being combined electronically from the two detectors.
  • Yaw insensitivity is again assured by the fact that any yaw misalignment affects the two reference marks in equal and opposite ways.
  • the magnetic detectors could be Hall sensors, reacting to reference marks which are magnetised; or they could be inductive sensors which detect marks made of a ferromagnetic material.
  • the reference marks and their detectors could interact capacitively .
  • reference tracks 14,16 there might not be reference tracks 14,16 on the scale itself.
  • the reference marks 18,20 could be provided on the substrate to which the main scale track 12 is affixed.
  • the main scale track itself could also be provided directly on the substrate.
  • the reference marks 18,20 need not be spaced at equal distances on opposite sides of the main scale track 12. They could be on opposite sides of the main scale track 12, but spaced by unequal amounts from it. Or they could both be on the same side of the main scale track, again spaced by unequal amounts from it. However, in either of these cases, yawing of the readhead will have unequal effects on the signals from the detectors. For accurate results, therefore, the detected reference mark position will require compensation by electronic or computer processing, depending on the differences in the respective reference mark positions detected by the two detectors, so such arrangements are not preferred.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)

Abstract

Le codeur décrit comprend une échelle (10) présentant un rail principal (12) d'échelle, le long duquel peut se déplacer une tête de lecture (22). L'échelle présente des marques de référence (18, 20), espacées latéralement de chaque côté du rail principal (12) de l'échelle. Un détecteur de marque de référence commun (30) produit un signal de sortie combiné lorsqu'il détecte les deux marques de référence (18, 20). Ce signal de sortie combiné établit la moyenne des erreurs d'Abbe des marques de référence, ce qui permet de réduire l'effet de tout mésalignement axial de lacet de la tête de lecture. Le détecteur de marque de référence commun peut éventuellement être remplacé par un détecteur respectif pour chaque marque de référence, dont les signaux de sortie sont combinés électroniquement.
PCT/GB2003/001087 2002-03-14 2003-03-14 Codeur a marques de reference WO2003079555A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003224235A AU2003224235A1 (en) 2002-03-14 2003-03-14 Encoder with reference marks

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0205972A GB0205972D0 (en) 2002-03-14 2002-03-14 Encoder with reference marks
GB0205972.3 2002-03-14

Publications (2)

Publication Number Publication Date
WO2003079555A2 true WO2003079555A2 (fr) 2003-09-25
WO2003079555A3 WO2003079555A3 (fr) 2004-04-01

Family

ID=9932922

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2003/001087 WO2003079555A2 (fr) 2002-03-14 2003-03-14 Codeur a marques de reference

Country Status (3)

Country Link
AU (1) AU2003224235A1 (fr)
GB (1) GB0205972D0 (fr)
WO (1) WO2003079555A2 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1923673A2 (fr) * 2006-11-20 2008-05-21 Dr. Johannes Heidenhain GmbH Dispositif de mesure de position
JP2014224745A (ja) * 2013-05-16 2014-12-04 株式会社ミツトヨ 原点信号発生装置及び原点信号発生システム
CN109477736A (zh) * 2016-05-25 2019-03-15 瑞尼斯豪公司 自适应参考标记检测过程

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114061631A (zh) * 2020-07-29 2022-02-18 中车株洲电力机车研究所有限公司 一种兆瓦级风机偏航计数器调节测试装置及方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0361867A2 (fr) * 1988-09-30 1990-04-04 Hewlett-Packard Company Dispositif de production d'index de codeur de mouvement insensible à la phase
EP0374614A2 (fr) * 1988-12-21 1990-06-27 PIRELLI CAVI S.p.A. Capteur optique et procédé pour déterminer la position d'un corps mobile
FR2777649A1 (fr) * 1998-04-16 1999-10-22 Jean Pierre Bazenet Dispositif de mesure incrementale de deplacement et de position de deux objets mobiles en translation l'un par rapport a l'autre
US6311572B1 (en) * 1997-12-09 2001-11-06 Mannesmann Vdo Ag Displacement sensor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0361867A2 (fr) * 1988-09-30 1990-04-04 Hewlett-Packard Company Dispositif de production d'index de codeur de mouvement insensible à la phase
EP0374614A2 (fr) * 1988-12-21 1990-06-27 PIRELLI CAVI S.p.A. Capteur optique et procédé pour déterminer la position d'un corps mobile
US6311572B1 (en) * 1997-12-09 2001-11-06 Mannesmann Vdo Ag Displacement sensor
FR2777649A1 (fr) * 1998-04-16 1999-10-22 Jean Pierre Bazenet Dispositif de mesure incrementale de deplacement et de position de deux objets mobiles en translation l'un par rapport a l'autre

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1923673A2 (fr) * 2006-11-20 2008-05-21 Dr. Johannes Heidenhain GmbH Dispositif de mesure de position
EP1923673A3 (fr) * 2006-11-20 2012-11-14 Dr. Johannes Heidenhain GmbH Dispositif de mesure de position
JP2014224745A (ja) * 2013-05-16 2014-12-04 株式会社ミツトヨ 原点信号発生装置及び原点信号発生システム
CN109477736A (zh) * 2016-05-25 2019-03-15 瑞尼斯豪公司 自适应参考标记检测过程

Also Published As

Publication number Publication date
GB0205972D0 (en) 2002-04-24
WO2003079555A3 (fr) 2004-04-01
AU2003224235A8 (en) 2003-09-29
AU2003224235A1 (en) 2003-09-29

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