GB1602006A - Ultrasonic distance measuring in apparatus having relatively movable parts - Google Patents

Ultrasonic distance measuring in apparatus having relatively movable parts Download PDF

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Publication number
GB1602006A
GB1602006A GB2128578A GB2128578A GB1602006A GB 1602006 A GB1602006 A GB 1602006A GB 2128578 A GB2128578 A GB 2128578A GB 2128578 A GB2128578 A GB 2128578A GB 1602006 A GB1602006 A GB 1602006A
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United Kingdom
Prior art keywords
pulse
transducer
comparator
return
burst
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Expired
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GB2128578A
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Cardiff University
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Cardiff University College
Cardiff University
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Publication date
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Priority to GB2128578A priority Critical patent/GB1602006A/en
Publication of GB1602006A publication Critical patent/GB1602006A/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G01S15/10—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S15/14—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves wherein a voltage or current pulse is initiated and terminated in accordance respectively with the pulse transmission and echo reception
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/523—Details of pulse systems
    • G01S7/526—Receivers
    • G01S7/527—Extracting wanted echo signals

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Description

(54) ULTRASONIC DISTANCE MEASURING IN APPARATUS HAVING RELATIVELY MOVABLE PARTS (71) We, UNIVERSITY COLLEGE CARDIFF, a British University College of Cardiff, Wales, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- The invention relates to distance measuring in apparatus having relatively movable parts and utilises ultrasonic techniques.
Usually, we prefer to use an ultrasonic pulse sustaining medium, such as oil or hydraulic fluid, that is normally present in the apparatus and between parts concerned during operation of that apparatus, for example a ram operated by a hydraulic fluid. In order to achieve low voltage operation, typically of the order of 12 volts or less, and to cope with sensing relatively close ^ and distant spacing of the parts concerning, we usually use an underdamped transducer on one part and interfacing directly with the pulse sustaining medium. It has been found that this can give rise to detection problems for relatively close and distant spacings of the parts as close spacing involves pulse returns within the resonance period of the transducer whereas returns for more distant spacings do not.This leads to threshold setting problems and it is one objective of the invention to provide for reliable detection of pulses regardless of the spacing between the parts.
According to the invention there is provided apparatus having relatively movable parts and between those parts, at least in operation, an hydraulic fluid serving as an ultrasonic wave sustaining medium, the apparatus further comprising an ultrasonic distance measuring system for measuring the distance between the parts, including transducer means for launching pulses or pulse bursts into the medium for reflection by a said part, and return pulse detection means including means operative on or after the transmission of a said pulse or pulse burst to provide a pulse return detection threshold that varies according to a prescribed characteristic.
Preferably the prescribed characteristic is substantially exponentially reducing.
It will normally be possible at least by mounting of a transducer, to ensure that there is a small but definite minimum pulse path length even at the closest spacing of the parts and corresponding to the worst of resonance effects. It may, too, be convenient to arrange that the threshold providing means has or is associated with pulse detection blanking means prior to imposition of a first level of threshold.
Another useful feature provided herein is that a transducer transmitting excitation be by way of antiphase signals applied across the transducer so that it is thereby possible to utilise absolute drive voltages that are one-half of the desired effective drive voltage.
Also, of course, although a preferred environment for implementing the invention is a low-voltage driven hydraulic system, such as a hydraulic ram in a mine working, embodiments of the invention are applicable elsewhere at low voltage, for example in chemical production plant or factories where explosive gases might be encountered, and embodiments of the invention are even more generally applicable without drive voltage restriction if detection problems arise, for example where it is convenient or desirable to utilise an underdamped transducer.
One specific embodiment of this invention will now be described, by way of example and with some indications as to alternatives, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a hydraulic ram extension detection system; Figure 2 shows a preferred ultrasonic transducer crystal exciting circuit or transmitter; Figure 2a illustrates excitation levels at points in that circuit and Figure 3 is a circuit diagram of a preferred receiver circuit.
In Figure 1, a hydraulic ram 10 has an ultrasonic transducer 11 mounted in a through-bore 12 in an end wall 13 of cylinder facing piston 14, though it could equally well be mounted in the piston 14 to face cylinder end wall 13, or even on either if maximum ram retraction will not then cause damage. If there is any chance of hydraulic fluid leaving a partlally unfilled volume of the cylinder, it is preferred, that the transducer 11 be located, at least in operation so as to be below hydraulic fluid connections to the cylinder and thereby reduce any prospect that intimate contact is ever lost between the transducer and the hydraulic fluid and/or facilitate extension measurement when the ram is not under load.
The transducer 11 is shown specifically as comprising an 0being double sealing brass housing 20 having an open end 21 tapering rearwardly at 22 to an offset entry 23 for electrical connecting conductors 24, 25 passing through a backing medium 26 of epoxy casting resin and entrained tungsten powder to a PXE type flat 1 MHz ultrasonic crystal 22 behind an ultrasonic coupling medium 28 such as epoxy resin alone. This transducer was suitably underdamped to give adequate sensitivity at drive voltages of about 12 volts, but it will be understood that any other desired form of transducer may be used.
The transducer 11 is connected to both a pulse type energising circuit or transmitter 30 and a receiver or return pulse detection circut 31.
The preferred transmitter 30 of Figure 2 has a clock pulse generator 32 that is or can be matched to the design operating frequency of the crystal 27. One suitable clock pulse generator comprises a cascade of three CMOS inverter gates operative as an oscillator by virtue of an interposed paralleled capacitor and a series ganged adjustable double potentiometer or variable resistor arrangement enabling precise tuning to the particular crystal. Output 33 from the clock is taken to a multi-stage binary counter 34 that, by its count capacity, determines intervals at which the crystal 27 is excited for transmission. For an approximately 4 milli-second interval using a lMHz crystal, a twelve-stage counter 34 with an all-stage zero-state detector 35 is suitable.Obviously an all-one-state detector could be used if, preferred or greater flexibility given by a presettable register/comparator arrangement on the register stage outputs. It is preferable to excite the crystal with a burst of pulses and an eight-pulse burst can be controlled using output 36 from the fourth counter stage.
Obviously, other counter stage outputs could be used to control other pulse burst lengths and a presettable register/comparator of short length could be used if desired.
The specifically shown all-zero detector 35 again uses CMOS gates for low power consumption, specifically a De Morgan "tree" of NOR gates 37 and NAND gates 38. Output 39 of the detector 35 and fourth counter stage output 36 are used to control a J-K m ster-slave flip flop 40 whose output 41 will thus produce an eight clock pulse width gating control signal at equal intervals corresponding to the capacity of the counter 34 A most useful feature of the preferred transmitter is in relation to minimising drive voltages of the crystal 27 and concerns applying excitation pulses to opposite faces thereof in antiphase thereby achieving for one particular value of drive voltage an effective drive of twice that voltage. Thus, for normal CMOS gate voltages of 6 volts an effective crystal drive voltage of 12 volts can be attained.To achieve this, Figure 2 shows output 41 from J-K flip flop 40 applied to two NAND gates 42, 43 having their other inputs energised at clock pulse rate, one (42) directly from the clock output 33 and the other (43) via an inverter 44 to give excitations as shown in Figure 2A.
Also shown in the drive to the crystal 27 are a pair of parallel diodes 46, 47 selected to give a low impedance on transmit and a high impedance on receive, receiver input being taken over line 48 including (see Figure 3) capacitor 49 to block any low frequency interference and paralleled by capacitor 50 to block any interference at frequencies above the crystal operating frequency, and thus effectively constituting a band-pass filter preferably centred on the crystal operating frequency, e.g. from 700 to 1500 for a IMHz crystal.
A two-input comparator 52 is used to detect reflected return pulses and is conveniently a differential operational amplifier operating in common mode with its inputs each connected via equal resistors 53, 54 to a nominal + supply voltage but offset to a desired permanent minimum threshold settable by resistor 55 between resistors 53 and 54. Resistor 56 connecting variable resistor 55 to the point of application of the received pulses over line 41 effectively provides a constant load resistance. Capacitor 57 connected between the other side of resistor 56 and ground serves to block any a.c. noise on the power supply from reaching that comparator input.Another capacitor 58 serves a similar purpose in relation to the other comparator input which also has connected thereto the above-mentioned exponential threshold circuit shown at 60 and operative immediately after crystal transmission of a pulse burst.
The exponential threshold circuit 60 is shown as an RC network comprising capacitor 61, variable resistor 62 connected between capacitor 58 and capacitor 61 in the other comparator input and serving to set the time constant of the RC thresholding network, and potentiometer 63 connected to the other side of the capacitor 61 and serving for amplitude setting with respect to an input thereto from the transmitter flipflop.
A blanking circuit 66 is also shown for preventing any receiver response to the initial resonance or ringing of the crystal 27.
This is conveniently achieved by using a bistable circuit 66 to detect the interval between transmitted and received return pulses with setting and resetting thereof controlled by a monostable circuit 67, setting being directly from the monostable via inverter 68 and resetting being via the blanking circuit 65 which comprises a NAND gate 69 having an output inverter 70 and inputs from inverter 68 and another inverter 71 from the comparator output.
The comparator is thus prevented from resetting the bistable 66 until after the monostable 65 has timed out. The monostable circuit 67 conveniently comprises CMOS NAND and inverter gates, capacitor 72 and variable resistor 73 to set a desired delay from transmitter output supply at 74.
Comparator output load resistor 75 serves to set desired output level thereof.
WHAT WE CLAIM IS: 1. Apparatus having relatively movable parts and between those parts, at least in operation, an hydraulic fluid serving as an ultrasonic wave sustaining medium, the apparatus further comprising an ultrasonic distance measuring system for measuring the distance between the parts, including transducer means for launching pulses or pulse bursts into the medium for reflection by a said part, and return pulse detection means including means operative on or after the transmission of a said pulse or pulse burst to provide a pulse return detection threshold that varies according to a prescribed characteristic.
2. Apparatus according to claim 1, wherein the prescribed characteristic starts high to correspond with and discriminate against resonance of the transducer means.
3. Apparatus according to claim 1 or claim 2, wherein the prescribed characteristic settles to a prescribed threshold after a predetermined time encompassing resonance of the transducer means.
4. Apparatus according to claim 2 or claim 3, wherein the prescribed characteristic is an exponential decay.
5. Apparatus according to claim 4, wherein the means for providing an exponentially decaying detection threshold comprises an RC network.
6. Apparatus according to any preceding claim, wherein a comparator of the detection means has one input for return pulses and another input for a reference signal level, the threshold setting means being coupled to said other input.
7. Apparatus according to claim 6, further comprising means for blocking from said comparator frequency components below a predetermined value itself below that of a said transducer means adapted for pulseburst operation.
8. Apparatus according to claim 6 or claim 7, further comprising means for blocking from said comparator frequency components higher than a predetermined value itself above that of a said transducer means adapted for pulse-burst operation.
9. Apparatus according to claim 7 or claim 8, wherein the or each further means comprises a capacitor.
10. Apparatus according to any preceding claim, further comprising means for disabling return pulse detection for a predetermined interval at least including transmission excitation of the transducer means.
11. Apparatus according to claim 10 with claim 7, wherein the means for disabling includes a coincidence logic gate between output of the comparator and a return pulse indicator.
12. Apparatus according to claim 11, wherein the return pulse indicator is a bistable device set or reset in response to transducer transmission excitation and reset or set by the comparator output on return pulse detection.
13. Apparatus according to claim 10, 11 or 12, wherein the means for disabling includes a monostable circuit set on transmission excitation of the transducer means and having a tim'e constant corresponding to the predetermined interval.
14. Apparatus according to any preceding claim, comprising means for exciting the transducer means to provide said pulse or pulse burst.
15. Apparatus according to claim 14, wherein the means for exciting comprises a clock pulse generator.
16. Apparatus according to claim 15, wherein the clock pulse generator has frequency tuning means to match the transducer means.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (27)

**WARNING** start of CLMS field may overlap end of DESC **. input which also has connected thereto the above-mentioned exponential threshold circuit shown at 60 and operative immediately after crystal transmission of a pulse burst. The exponential threshold circuit 60 is shown as an RC network comprising capacitor 61, variable resistor 62 connected between capacitor 58 and capacitor 61 in the other comparator input and serving to set the time constant of the RC thresholding network, and potentiometer 63 connected to the other side of the capacitor 61 and serving for amplitude setting with respect to an input thereto from the transmitter flipflop. A blanking circuit 66 is also shown for preventing any receiver response to the initial resonance or ringing of the crystal 27. This is conveniently achieved by using a bistable circuit 66 to detect the interval between transmitted and received return pulses with setting and resetting thereof controlled by a monostable circuit 67, setting being directly from the monostable via inverter 68 and resetting being via the blanking circuit 65 which comprises a NAND gate 69 having an output inverter 70 and inputs from inverter 68 and another inverter 71 from the comparator output. The comparator is thus prevented from resetting the bistable 66 until after the monostable 65 has timed out. The monostable circuit 67 conveniently comprises CMOS NAND and inverter gates, capacitor 72 and variable resistor 73 to set a desired delay from transmitter output supply at 74. Comparator output load resistor 75 serves to set desired output level thereof. WHAT WE CLAIM IS:
1. Apparatus having relatively movable parts and between those parts, at least in operation, an hydraulic fluid serving as an ultrasonic wave sustaining medium, the apparatus further comprising an ultrasonic distance measuring system for measuring the distance between the parts, including transducer means for launching pulses or pulse bursts into the medium for reflection by a said part, and return pulse detection means including means operative on or after the transmission of a said pulse or pulse burst to provide a pulse return detection threshold that varies according to a prescribed characteristic.
2. Apparatus according to claim 1, wherein the prescribed characteristic starts high to correspond with and discriminate against resonance of the transducer means.
3. Apparatus according to claim 1 or claim 2, wherein the prescribed characteristic settles to a prescribed threshold after a predetermined time encompassing resonance of the transducer means.
4. Apparatus according to claim 2 or claim 3, wherein the prescribed characteristic is an exponential decay.
5. Apparatus according to claim 4, wherein the means for providing an exponentially decaying detection threshold comprises an RC network.
6. Apparatus according to any preceding claim, wherein a comparator of the detection means has one input for return pulses and another input for a reference signal level, the threshold setting means being coupled to said other input.
7. Apparatus according to claim 6, further comprising means for blocking from said comparator frequency components below a predetermined value itself below that of a said transducer means adapted for pulseburst operation.
8. Apparatus according to claim 6 or claim 7, further comprising means for blocking from said comparator frequency components higher than a predetermined value itself above that of a said transducer means adapted for pulse-burst operation.
9. Apparatus according to claim 7 or claim 8, wherein the or each further means comprises a capacitor.
10. Apparatus according to any preceding claim, further comprising means for disabling return pulse detection for a predetermined interval at least including transmission excitation of the transducer means.
11. Apparatus according to claim 10 with claim 7, wherein the means for disabling includes a coincidence logic gate between output of the comparator and a return pulse indicator.
12. Apparatus according to claim 11, wherein the return pulse indicator is a bistable device set or reset in response to transducer transmission excitation and reset or set by the comparator output on return pulse detection.
13. Apparatus according to claim 10, 11 or 12, wherein the means for disabling includes a monostable circuit set on transmission excitation of the transducer means and having a tim'e constant corresponding to the predetermined interval.
14. Apparatus according to any preceding claim, comprising means for exciting the transducer means to provide said pulse or pulse burst.
15. Apparatus according to claim 14, wherein the means for exciting comprises a clock pulse generator.
16. Apparatus according to claim 15, wherein the clock pulse generator has frequency tuning means to match the transducer means.
17. Apparatus according to claim 14, 15
or 16, wherein the means for exciting has pulse or pulse-burst interval timing means.
18. Apparatus according to claim 17 with claim 15, wherein the timing means comprises a counter driven by the clock pulse generator and means for detecting a predetermined state of the counter.
19. Apparatus according to claim 18, wherein the last-mentioned means is responsive to all counter stages having the same state.
20. Apparatus according to any one of claims 14 to 19, wherein the means for exciting comprises means for timing the duration of a said pulse-burst.
21. Apparatus according to claim 20 with claim 18, wherein the last-mentioned means is responsive to an intermediate state of the counter.
22. Apparatus according to claim 21 with claim 8, comprising a bistable device controlled in accordance with pulse burst interval timing and pulse burst duration timing signals.
23. Apparatus according to claim 22, wherein the bistable device is associated with logic gate means for passing or blocking clock pulses relative to the transducer means.
24. Apparatus according to any one of claims 14 to 23, wherein the means for exciting includes means for applying signals corresponding to said pulse or pulse-bursts in antiphase to opposite sides of an ultrasonic crystal of the transducer means.
25. Apparatus according to claim 24 with claim 23, wherein said logic gate means comprises a pair of coincidence gates enabled simultaneously by the bistable device and connected to receive clock pulses in anti-phase.
26. Apparatus according to any preceding claim, wherein the hydraulic apparatus is a ram whose cylinder and piston constitute said parts.
27. Apparatus having relatively movable parts and for measuring the distance between those parts an ultrasonic distance measuring system arranged and adapted to operate substantially as herein described with reference to Figure 3 or to Figures 2 and 3 or the Figures 1, 2 and 3 of the accompanying drawings.
GB2128578A 1978-05-23 1978-05-23 Ultrasonic distance measuring in apparatus having relatively movable parts Expired GB1602006A (en)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3031980A1 (en) * 1980-08-25 1982-04-01 Johannes 8000 München König Hydraulic cylinder piston position measuring system - uses propagation time of ultrasonic pulses reflected from end face of piston
DE3116333A1 (en) * 1981-04-24 1982-11-18 H. Kuhnke Gmbh Kg, 2427 Malente Measuring system for contactlessly detecting positions of the piston rod of a piston/cylinder unit
WO1983003478A1 (en) * 1982-03-30 1983-10-13 Martin Reuter Method and installation for determining a relative distance in a cylinder and piston device
GB2172995A (en) * 1985-03-30 1986-10-01 Emhart Ind Monitoring the position of a member
GB2207757A (en) * 1987-08-07 1989-02-08 Sonin Inc Ultrasonic rangefinder
GB2279746A (en) * 1993-06-29 1995-01-11 Samsung Electronics Co Ltd Ultrasonic distance measurement
DE102017129445A1 (en) * 2017-11-10 2019-05-16 Grob-Werke Gmbh & Co. Kg Method and device for determining the position of a piston of a hydraulic cylinder of a machine tool

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3031980A1 (en) * 1980-08-25 1982-04-01 Johannes 8000 München König Hydraulic cylinder piston position measuring system - uses propagation time of ultrasonic pulses reflected from end face of piston
DE3116333A1 (en) * 1981-04-24 1982-11-18 H. Kuhnke Gmbh Kg, 2427 Malente Measuring system for contactlessly detecting positions of the piston rod of a piston/cylinder unit
WO1983003478A1 (en) * 1982-03-30 1983-10-13 Martin Reuter Method and installation for determining a relative distance in a cylinder and piston device
GB2172995A (en) * 1985-03-30 1986-10-01 Emhart Ind Monitoring the position of a member
GB2207757A (en) * 1987-08-07 1989-02-08 Sonin Inc Ultrasonic rangefinder
GB2207757B (en) * 1987-08-07 1991-09-04 Sonin Inc Apparatus for measuring distances
GB2279746A (en) * 1993-06-29 1995-01-11 Samsung Electronics Co Ltd Ultrasonic distance measurement
DE102017129445A1 (en) * 2017-11-10 2019-05-16 Grob-Werke Gmbh & Co. Kg Method and device for determining the position of a piston of a hydraulic cylinder of a machine tool

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