Classifications

• • 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
  • G01D5/2451—Incremental encoders
• • 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

Definitions

• the present invention relates to scale reading apparatus.
• the invention relates to scale reading apparatus having limit switches and reference marks.
• a known form of scale reading apparatus for measuring relative displacement of two members comprises a scale on one of the members having scale marks defining a pattern and a readhead provided on the other member.
• An optical scale reading apparatus has means for illuminating the scale, a detecting means in the readhead responsive to resultant light patterns to produce a measure of relative displacement of the scale and readhead.
• a scale having its marks in a periodic pattern is known as an incremental scale and provides an output of up and down counts .
• a scale may be provided with reference marks which when detected by the readhead enable the exact position of the readhead to be determined.
• Mass produced scale may have an incremental track and a plurality of reference marks. The user may wish to use some of these reference marks but not others.
• the end points of movement of the machine part are defined by limit switches. These for example may be mechanical, magnetic or optical.
• the present invention provides a scale for a scale reading apparatus comprising: a track having scale markings; markers of two or more different states; wherein different combinations of the two or more different states of markers provide different functions .
• the markers have different states if they can be differentiated, i.e. they may be different types of markers or may be the same type of marker on different tracks .
• the track may comprise an incremental track.
• the incremental track may include at least one reference mark.
• reference marks may be provided in an additional track parallel to the track.
• Markers of two states may be combined to produce four output states, i.e. no markers of either state, a single marker of a first state, a single marker of a second type, and markers of both first and second state.
• the functions of the different marker combinations may for example comprise a reference mark enabler and limit switches .
• Markers of a first state may be provided on a first additional track and markers of a second state may be provided on a second additional track.
• the first and second markers may be otherwise identical.
• two different states of markers may be provided on a single track.
• a marker of a first state acts as a first limit switch
• a marker of a second state acts as a reference mark enabler
• markers of both first and second states act as a second limit switch
• the marker of the second state may extend further than the marker for the first state on at least one side. This has the advantage that if the readhead is yawed, it will never detect the marker of the first state before the marker of the second state. Thus the function of the double marker (in this case the second limit switch) cannot be mistaken for the function of the marker of a first state (in this case the first limit switch) .
• the marker of the second state may extend further than the marker of the first state on at least one side by a distance less than x, and at the position of a marker only of the second state, the marker may have a length of greater than x.
• This has the advantage that if a marker of the second state is detected, it can be confirmed whether there is also a marker of the first state by moving the readhead a distance x.
• the position of the markers may be adjustable and are suitable for adjustment by an end user.
• the markers may comprise stickers, magnets or releasably mounted in fixing holes.
• Fig 1 is a side view of a scale and readhead
• Fig 2 is a plan view of a first embodiment of the scale
• Fig 3 is a plan view of part of the scale of Fig 2 and a yawed readhead
• Fig 4 is a plan view of a second embodiment of the scale.
• Fig 1 illustrates a scale 10 mounted on a first machine part (not shown) and a readhead 12 mounted on a second machine part (not shown) .
• the second machine part and thus the readhead being movable relative to the scale.
• Fig 2 illustrates the scale 10 which has an incremental track 14 comprising a periodic pattern of scale marks 16 made up of alternate reflecting and non-reflecting lines.
• Reference marks 18 are embedded in the incremental scale. These may be embedded by removing or adding scale marks for example. Alternatively reference marks may be provided in a separate scale track. When there are several reference marks, the end user may wish to select a particular reference mark and ignore the other reference marks.
• two additional tracks 20,22 are provided on either side of the incremental track 14. Markers in these two tracks may be used for limit switches and to enable reference marks.
• a single marker 24 in track 22 indicates the left limit switch
• a single marker 30 in track 20 is a reference mark enabler and markers 26 in track 22 and 28 in track 20 act as a right limit switch.
• the combination of a single marker in track 20, a single marker in track 22, or markers in both the tracks 20 and 22 can be used to indicate three different functions, i.e. the left and right limit switches and an enabled reference mark.
• the readhead 12 is provided with standard incremental optics 2 for reading the incremental scale, reference mark sensing optics (not shown) for reading the reference mark and two reflective optical sensors 4,6 for detecting the markers in tracks 20,22.
• the reflective optical sensors 4,6 may be offset from the incremental optics 2 in the longitudinal direction.
• the reference mark enabler 30 may be correspondingly offset from the reference mark 32.
• the readhead 12 is yawed, as shown in Fig 3, or if the markers are not accurately positioned, it is possible that when the readhead passes over the right limit switch it would detect one of marks 28 and 26 before the other and thus mistake the right limit switch for either a reference mark enabler (if mark 28 in track 20 is detected first) or the left limit switch (if mark 26 in track 22 is detected first) . In particular if the right light switch is mistaken for the left limit switch no signal will be sent to the moving machine part to stop movement and the moving machine part will move too far.
• the layout of the double marker representing the right limit switch is altered. As shown in Fig 4, mark 28 in track 20 is extended past mark 26 in track 22 in both directions, ensuring that mark 28 is always read before mark 26. Thus in this arrangement the right limit switch cannot be mistaken for the left limit switch as the arrangement does not allow for the mark 26 in track 22 to be detected without a mark in track 20.
• a rule is given to the readhead that it must travel a distance x (for example 2mm) before it switches on the reference mark sensor.
• the marker 30 acting as a reference mark enabler must extend at least distance x either side of reference mark 32.
• the overhang of marker 28 over marker 26 must be less than distance x.
• the readhead when the readhead is moving over the right limit switch, after detecting marker 28 in track 22 it will detect marker 26 in track 22 within distance x and thus detect the right limit switch.
• the readhead When the readhead is positioned over the reference mark enabler marker 30, it will travel distance x in either direction and not pick up any mark in track 22 thus detecting a reference mark enabler.
• the combination of markers can be differentiated from each other when the readhead is turned on.
• the marker 24 is identified as the left light switch as this is the only scenario when there is a mark only in track 22.
• both the markers 26,28 are detected and thus there is no confusion.
• Figs 1-4 illustrate a reflective system.
• the invention is also suitable for a transmissive system.
• the position of the markers on tracks 20 and 22 are preferably detected by photodetectors in the readhead.
• the markers could be dark on a reflective background.
• the markers could comprise a device such as a chamfered surface, prism or diffraction grating which directs light in a different direction to the rest of the surface.
• the markers are adjustable, for example they may comprise stickers, slides or be attachable magnetically.
• the markers could be non- optical for example magnetic and could be detected by sensors (e.g. Hall sensors) in the readhead.
• This invention is suitable with different types of scale, for example capacitance, inductive, magnetic and optical incremental scales.
• the markers may be placed in a single track.
• markers for different colours may be used, for example a blue marker for the left limit switch, a red marker for a reference mark enabler and both blue and red markers for the right limit switch.
• the readhead would thus have detectors that are sensitive to the different colour markings.
• this invention is also suitable for a partial arc on a rotary scale.
• the invention is also suitable for a mid travel limit and for multiple limits allowing the use of multiple readheads on a single axis system.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Transmission And Conversion Of Sensor Element Output (AREA)

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• 2004
  • 2004-06-21 GB GBGB0413711.3A patent/GB0413711D0/en not_active Ceased
• 2005
  • 2005-06-21 WO PCT/GB2005/002442 patent/WO2005124288A1/en not_active Ceased
  • 2005-06-21 EP EP05759442A patent/EP1769221A1/en not_active Withdrawn
  • 2005-06-21 US US11/629,466 patent/US7421800B2/en not_active Expired - Fee Related
  • 2005-06-21 JP JP2007517446A patent/JP2008503747A/ja active Pending
  • 2005-06-21 CN CNB2005800204084A patent/CN100523738C/zh not_active Expired - Fee Related

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