WO2001020263A1 - Position sensor - Google Patents

Position sensor Download PDF

Info

Publication number
WO2001020263A1
WO2001020263A1 PCT/GB2000/003446 GB0003446W WO0120263A1 WO 2001020263 A1 WO2001020263 A1 WO 2001020263A1 GB 0003446 W GB0003446 W GB 0003446W WO 0120263 A1 WO0120263 A1 WO 0120263A1
Authority
WO
WIPO (PCT)
Prior art keywords
drum
position sensor
sensor
movable member
actuator
Prior art date
Application number
PCT/GB2000/003446
Other languages
French (fr)
Inventor
David Mark Hampson
Original Assignee
Huntleigh Technology 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 Huntleigh Technology Plc filed Critical Huntleigh Technology Plc
Priority to AU70247/00A priority Critical patent/AU7024700A/en
Publication of WO2001020263A1 publication Critical patent/WO2001020263A1/en

Links

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

Definitions

  • the invention relates to a position sensor and particularly an encoder device for determining the absolute position as well as the incremental position of a movable member .
  • a motor driven linear actuator consists of a rotary motor, driving a gear mechanism that converts the rotary motion into linear movement of an actuator. Typically for each revolution of the motor, the actuator will progress by a predetermined distance, according to the gearing ratio. The motor is reversed to drive the actuator in the opposite direction. As the motor rotates a sensor counts the revolutions or part revolutions. If the actuator starts from a known position the number of counts up or down will determine the new position relative to the reference position.
  • the advantage of this system is that the pulses can be provided by a cheap and simple counting device.
  • the disadvantage with such a relative encoder is that the original reference position must be known. This may be lost during power off, mechanical slippage, or if the actuator is moved when the pulse sensor is not active.
  • Absolute encoders that indicate the position at any point may include multi -channel sensor arrays which provide a different digital code combination for a set number of positions, or multi-turn potentiometers which give a resistance value relative to the absolute position.
  • the disadvantages of both systems are costs and complexity.
  • the aim of the invention is to provide a simple encoder that provides absolute as well as relative position sensing.
  • the invention provides a position sensor for a movable member, the position sensor comprising encoding means having at least one coded track, a detection means for detecting elements of the track, wherein the code on the track is unique to a particular position on the encoding means, representing a direct relationship to the position of the movable member.
  • the detection means provides a chain of pulses representative of the position of the movable member.
  • the detection means is an optical sensor.
  • the coded track includes a drum with a black and white pattern printed along its length.
  • the coded track includes steps at each end to mark end stops for travel of the movable member. This avoids the necessity of additional mechanical limit switches or motor current sensing.
  • the encoder mark/space printing on the drum is varied along its length.
  • an optical sensor views a small point on the encoder drum.
  • the drum is connected to the motor shaft by a sliding coupling so that as the motor rotates the drum also rotates and at the same time is driven forwards or backwards on the motor shaft according to the movement of the actuator. Therefore, the mark/space ratio sensed by the optical sensor at a particular point, indicates a particular position on the drum, from which can be derived the number of motor revolutions and hence position of the actuator.
  • the pulses are generated from an optical sensor, sensing black lines on a white background, printed on a rotating drum, connected to the shaft of a rotary motor, driving an actuator.
  • each period consists of black sensing on time - mark, and a white sensing off time - space, therefore according to the invention, for each pulse, the mark/space ratio is unique to a particular position on the encoder drum, which bears a direct relationship to the actuator position. As the actuator operates, a chain of pulses count the motor shaft revolutions .
  • Figure 1 is an exploded view of a preferred embodiment of the invention
  • Figure 2 is a cross sectional view of the drum and mounting plate in Figure 1 ;
  • Figure 3 is another embodiment of the invention.
  • Figure 4 illustrates the encoder signal received from the optical sensor of the invention.
  • the position sensor 1 is driven from the output shaft 8 of the worm gear 13.
  • the output shaft 8 drives the linear screw arm of the actuator (not shown) .
  • the actuator may progress 6mm per shaft revolution, so that 50 turns will give an actuator stroke of 300mm.
  • the encoder drum 1, is conveniently a plastic moulding, which fits directly onto the output shaft 8.
  • the outside surface of the drum 1 is covered by a self- adhesive label, onto which the encoder pattern is printed, in this case the black area 11 and white area 12.
  • the optical sensor carrier 2 may also be a plastic moulding.
  • the optical sensor 3 consists of a light emitting diode and phototransistor mounted on a small printed circuit board connected to the control system. The sensor pair detect the difference between black and white reflected light off the encoder drum printing.
  • the carrier 2 is connected to slide with respect to the drum 1 by a screw thread 4.
  • the optical sensor carrier 2 is restrained from rotation with the drum 1 by slide pin 6, that fits through a clearance hole in the carrier 2, and locates into the worm gearbox housing by means of bush 7.
  • the internal thread insert 5 acts on the screw thread 4, causing the carrier 2 to move along the axis of the drum 1.
  • the sensor 2 detects the black and white marks around the circumference of the drum 1.
  • the pattern on the drum may also show a step change at each end to indicate end stops.
  • the mark/space ratio detected by the optical sensor 3 varies according to its position along the length of the drum.
  • the mark space ratio detected is used by the control system to determine the position of the encoder drum 1, which bears a direct relation to the number of turns of the gearbox output shaft 8, which has a direct relationship to the linear actuator position. Furthermore, an additional gearbox may be placed between the rotating drum 1 and screw thread 4 on the optical sensor carrier 2 in order to obtain an increased number of rotations of the drum 1 relative to the sensor 3. In order to sense the direction of travel of the actuator, a second optical sensor may be positioned offset relative to the first sensor 3. Direction of travel can be determined by comparison of the two sensor output codes .
  • Figure 3 shows an alternative embodiment wherein the optical sensor is stationary and the encoder drum moves relative to it. The pulses generated by the sensor for both embodiments are illustrated in Figure 4.
  • Each period consists of black sensing on time - mark, and a white sensing off time - space, therefore for each pulse, the mark/space ratio is unique to a particular position on the encoder drum, which bears a direct relationship to the actuator position.
  • a chain of pulses count the motor shaft revolutions.
  • other distinctive patterns may be used. For example distinctive codes could be used as a narrow band at each end of the drum surface to act as end stop warnings. Also, distinctive pattern bands could be used along the length of the drum as reference points for the actuator.
  • the same position sensing may be achieved by means of an optical transmissive sensor, reading a code perforated into the drum, or a mechanical microswitch reading a code engraved in relief on a drum or a magnetic sensor reading a code on a magnetic label attached to the drum surface .
  • the encoder may be used on other devices, as well as linear actuators.
  • the encoder can be applied to any device where a rotary motor is used to position an item within a limited travel, for example, where a work head is positioned relative to a work piece, robot arms, or car seat positions.

Abstract

A position sensor for a movable member consists of an encoder drum (1) driven by a motor shaft (8) also driving the movable member. The drum (1) is covered with a self adhesive label with an encoder pattern printed on it. An optical sensor (3) located on a sliding carrier (2) detects the difference between the black and white reflected light off the drum printing and generates a chain of pulses representative of the position of the movable member. For each pulse, the black and white ratio is unique to a particular position on the encoder drum which bears a direct relationship to the movable member position. The position sensor can measure absolute as well as incremental position of a movable member.

Description

POSITION SENSOR
The invention relates to a position sensor and particularly an encoder device for determining the absolute position as well as the incremental position of a movable member .
It is known to have single channel encoder devices having a single channel digital pulse output used to determine relative incremental positions of a linear actuator.
A motor driven linear actuator consists of a rotary motor, driving a gear mechanism that converts the rotary motion into linear movement of an actuator. Typically for each revolution of the motor, the actuator will progress by a predetermined distance, according to the gearing ratio. The motor is reversed to drive the actuator in the opposite direction. As the motor rotates a sensor counts the revolutions or part revolutions. If the actuator starts from a known position the number of counts up or down will determine the new position relative to the reference position. The advantage of this system is that the pulses can be provided by a cheap and simple counting device. The disadvantage with such a relative encoder is that the original reference position must be known. This may be lost during power off, mechanical slippage, or if the actuator is moved when the pulse sensor is not active. To compensate, the actuator would have to be regularly rechecked at the reference position, which in itself can result in operational compromises. Absolute encoders that indicate the position at any point may include multi -channel sensor arrays which provide a different digital code combination for a set number of positions, or multi-turn potentiometers which give a resistance value relative to the absolute position. The disadvantages of both systems are costs and complexity.
The aim of the invention is to provide a simple encoder that provides absolute as well as relative position sensing.
Accordingly, the invention provides a position sensor for a movable member, the position sensor comprising encoding means having at least one coded track, a detection means for detecting elements of the track, wherein the code on the track is unique to a particular position on the encoding means, representing a direct relationship to the position of the movable member.
Preferably, the detection means provides a chain of pulses representative of the position of the movable member. Preferably, the detection means is an optical sensor. Preferably, the coded track includes a drum with a black and white pattern printed along its length.
Preferably, the coded track includes steps at each end to mark end stops for travel of the movable member. This avoids the necessity of additional mechanical limit switches or motor current sensing. Preferably, the encoder mark/space printing on the drum is varied along its length. Preferably, an optical sensor views a small point on the encoder drum.
Conveniently, the drum is connected to the motor shaft by a sliding coupling so that as the motor rotates the drum also rotates and at the same time is driven forwards or backwards on the motor shaft according to the movement of the actuator. Therefore, the mark/space ratio sensed by the optical sensor at a particular point, indicates a particular position on the drum, from which can be derived the number of motor revolutions and hence position of the actuator. In a preferred embodiment, the pulses are generated from an optical sensor, sensing black lines on a white background, printed on a rotating drum, connected to the shaft of a rotary motor, driving an actuator. Preferably, for each pulse, each period consists of black sensing on time - mark, and a white sensing off time - space, therefore according to the invention, for each pulse, the mark/space ratio is unique to a particular position on the encoder drum, which bears a direct relationship to the actuator position. As the actuator operates, a chain of pulses count the motor shaft revolutions .
The invention will now be described by way of example only with reference to the following in which:
Figure 1 is an exploded view of a preferred embodiment of the invention;
Figure 2 is a cross sectional view of the drum and mounting plate in Figure 1 ;
Figure 3 is another embodiment of the invention; and Figure 4 illustrates the encoder signal received from the optical sensor of the invention.
Referring to Figure 1, the position sensor 1 is driven from the output shaft 8 of the worm gear 13. The output shaft 8 drives the linear screw arm of the actuator (not shown) . Typically the actuator may progress 6mm per shaft revolution, so that 50 turns will give an actuator stroke of 300mm. The encoder drum 1, is conveniently a plastic moulding, which fits directly onto the output shaft 8. The outside surface of the drum 1 is covered by a self- adhesive label, onto which the encoder pattern is printed, in this case the black area 11 and white area 12.
The optical sensor carrier 2, may also be a plastic moulding. The optical sensor 3, consists of a light emitting diode and phototransistor mounted on a small printed circuit board connected to the control system. The sensor pair detect the difference between black and white reflected light off the encoder drum printing.
The carrier 2 is connected to slide with respect to the drum 1 by a screw thread 4. The optical sensor carrier 2 is restrained from rotation with the drum 1 by slide pin 6, that fits through a clearance hole in the carrier 2, and locates into the worm gearbox housing by means of bush 7.
As the drum 1 rotates, the internal thread insert 5 acts on the screw thread 4, causing the carrier 2 to move along the axis of the drum 1. As the optical sensor 3 moves alongside the surface of the drum 1, the sensor 2 detects the black and white marks around the circumference of the drum 1. The pattern on the drum may also show a step change at each end to indicate end stops. The mark/space ratio detected by the optical sensor 3 varies according to its position along the length of the drum.
The mark space ratio detected is used by the control system to determine the position of the encoder drum 1, which bears a direct relation to the number of turns of the gearbox output shaft 8, which has a direct relationship to the linear actuator position. Furthermore, an additional gearbox may be placed between the rotating drum 1 and screw thread 4 on the optical sensor carrier 2 in order to obtain an increased number of rotations of the drum 1 relative to the sensor 3. In order to sense the direction of travel of the actuator, a second optical sensor may be positioned offset relative to the first sensor 3. Direction of travel can be determined by comparison of the two sensor output codes . Figure 3 shows an alternative embodiment wherein the optical sensor is stationary and the encoder drum moves relative to it. The pulses generated by the sensor for both embodiments are illustrated in Figure 4. Each period consists of black sensing on time - mark, and a white sensing off time - space, therefore for each pulse, the mark/space ratio is unique to a particular position on the encoder drum, which bears a direct relationship to the actuator position. As the actuator operates, a chain of pulses count the motor shaft revolutions. In addition to the mark/space ratio pattern, other distinctive patterns may be used. For example distinctive codes could be used as a narrow band at each end of the drum surface to act as end stop warnings. Also, distinctive pattern bands could be used along the length of the drum as reference points for the actuator.
Although the embodiments have shown a drum with a an optical sensor, the same position sensing may be achieved by means of an optical transmissive sensor, reading a code perforated into the drum, or a mechanical microswitch reading a code engraved in relief on a drum or a magnetic sensor reading a code on a magnetic label attached to the drum surface .
The encoder may be used on other devices, as well as linear actuators. The encoder can be applied to any device where a rotary motor is used to position an item within a limited travel, for example, where a work head is positioned relative to a work piece, robot arms, or car seat positions.

Claims

CLAIMS ;
1. A position sensor for a movable member, the position sensor comprising encoding means having at least one coded 5 track, a detection means for detecting elements of the track, wherein the code on the track is unique to a particular position on the encoding means, representing a direct relationship to the position of the movable member.
102. A position sensor as claimed in claim 1 wherein the detection means is an optical sensor.
3. A position sensor as claimed in claims 1 or 2 wherein the coded track includes a drum with a black and white
15 mark/space printing along its length.
4. A position sensor as claimed in claim 3 wherein the coded track includes steps at each end to indicate end stops .
20
5. A position sensor as claimed in claims 3 or 4 wherein the mark/space printing on the drum is varied along its length.
256. A position sensor as claimed in claims 2 to 5 wherein an optical sensor views a small point on the encoder drum.
7. A position sensor as claimed in any preceding claim wherein the drum is connected to a motor shaft by a
30 sliding coupling so that as the motor rotates the drum also rotates and at the same time is driven forwards or backwards on the motor shaft according to the movement of an actuator driven by the motor.
8. A position sensor as claimed in claims 2 to 7 wherein the optical sensor detects black lines on a white background printed on the rotating drum and generates pulses according to the revolutions of the drum which is directly connected to the shaft of a rotary motor driving an actuator.
9. A position sensor as claimed in claim 8 wherein for each pulse, each period consists of black sensing mark, and a white sensing space, the mark/space ratio being unique to a particular position on the drum, and bearing a direct relationship to the actuator position.
PCT/GB2000/003446 1999-09-11 2000-09-08 Position sensor WO2001020263A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU70247/00A AU7024700A (en) 1999-09-11 2000-09-08 Position sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9921421.5A GB9921421D0 (en) 1999-09-11 1999-09-11 Position sensor
GB9921421.5 1999-09-11

Publications (1)

Publication Number Publication Date
WO2001020263A1 true WO2001020263A1 (en) 2001-03-22

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ID=10860703

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2000/003446 WO2001020263A1 (en) 1999-09-11 2000-09-08 Position sensor

Country Status (3)

Country Link
AU (1) AU7024700A (en)
GB (2) GB9921421D0 (en)
WO (1) WO2001020263A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1734744A2 (en) * 2005-06-15 2006-12-20 Samsung Electronics Co.,Ltd. Camera lens assembly for portable terminals
WO2020118253A1 (en) * 2018-12-07 2020-06-11 Smith Kevin S Valve indicator and related methods

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989007058A1 (en) * 1988-02-08 1989-08-10 Zahnradfabrik Friedrichshafen Ag Vehicle with driven steering axle
DE4411553A1 (en) * 1994-04-02 1995-10-05 Bosch Gmbh Robert Device for sensing a rotational movement and an axial displacement of a body
DE19522840A1 (en) * 1994-07-01 1996-01-04 Volkswagen Ag Motor vehicle transmission pulley rotation sensor
US5602681A (en) * 1994-04-11 1997-02-11 Sony Corporation Lens barrel for a video camera, and linear feeding system thereof

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2149500A (en) * 1983-11-09 1985-06-12 British Aerospace Sensing systems
EP0441963A4 (en) * 1989-07-07 1991-11-21 Kabushiki Kaisha Yaskawa Denki Seisakusho Absolute value encoder
GB9022969D0 (en) * 1990-10-23 1990-12-05 Rosemount Ltd Displacement measurement apparatus
GB2354372A (en) * 1999-09-17 2001-03-21 Damco Ltd Connector module and encoder arrangement for an electic motor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989007058A1 (en) * 1988-02-08 1989-08-10 Zahnradfabrik Friedrichshafen Ag Vehicle with driven steering axle
DE4411553A1 (en) * 1994-04-02 1995-10-05 Bosch Gmbh Robert Device for sensing a rotational movement and an axial displacement of a body
US5602681A (en) * 1994-04-11 1997-02-11 Sony Corporation Lens barrel for a video camera, and linear feeding system thereof
DE19522840A1 (en) * 1994-07-01 1996-01-04 Volkswagen Ag Motor vehicle transmission pulley rotation sensor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1734744A2 (en) * 2005-06-15 2006-12-20 Samsung Electronics Co.,Ltd. Camera lens assembly for portable terminals
EP1734744A3 (en) * 2005-06-15 2008-02-13 Samsung Electronics Co.,Ltd. Camera lens assembly for portable terminals
WO2020118253A1 (en) * 2018-12-07 2020-06-11 Smith Kevin S Valve indicator and related methods

Also Published As

Publication number Publication date
GB2357836A (en) 2001-07-04
GB0022056D0 (en) 2000-10-25
AU7024700A (en) 2001-04-17
GB9921421D0 (en) 1999-11-10

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