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AE4-S02 Spacecraft Mechatronics Displacement Sensors. Dr. ir. W. Jongkind TU-Delft 2004 – 2005. Introduction (1). Potentiometers. Linear as well as rotary potentiometer are applied. Potentiometers are used in situations where accuracy is not of major importance,

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ae4 s02 spacecraft mechatronics displacement sensors

AE4-S02 Spacecraft MechatronicsDisplacement Sensors

Dr. ir. W. Jongkind

TU-Delft

2004 – 2005

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

introduction 1
Introduction (1)
  • Potentiometers. Linear as well as rotary potentiometer are applied.
    • Potentiometers are used in situations where accuracy is not of major importance,
    • Accuracies may vary from 0.3 % to 5 %.
    • Device is normally cheap.
  • Incremental Encoders.Linear and rotary incremental encoders are applied.
    • Rather inexpensive devices.
    • The performance depends on the resolution of the encoder slit pattern.
    • They can can be very accurate indeed.

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

introduction 2
Introduction (2)
  • Absolute Encoders. Again linear and rotary absolute encoders exist
    • The code pattern is in the majority of cases a Gray code pattern, binary code patterns are much less common
  • Electrical Transformers
    • For very accurate linear displacement measurements often Linear Variable Differential Transformers (LVDT)are applied
    • The rotary displacement can be accurately measured with rotary electrical transformer devices such as the Resolver or Synchro

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

making the right choice
Making the Right Choice
  • The following requirements and constraint should be addressed:
    • Required resolution
    • Required accuracy
    • Environmental constraints
    • Integration aspects
    • Availability
  • The selected displacement sensor is the most important factor and deciding for overall performance of a system especially when the device forms part of a feedback loop

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

potentiometer 1
Potentiometer (1)
  • Operating range from 1 mm to 1m

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

potentiometer 2
Potentiometer (2)

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

encoders
Encoders
  • Typically used as shaft angle encoders
  • The device output is in digital form
    • Digital output needs in general to be transformed with the aid of a computing device to obtain magnitude and direction of movement as well as position or angle information
  • Consist of a pattern impressed upon a part of the system that characterizes the motion
  • Two main classes of optical encoders:
    • Absolute encoders and
    • Incremental encoders
    • For velocity measurement nearly always incremental encoders are applied

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

incremental encoder
Incremental Encoder

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

readout system
Readout System

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

sense of rotation
Sense of Rotation

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

linear encoder codes
Linear Encoder Codes

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

circular encoder codes
Circular Encoder Codes

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

gray encoder output
Gray Encoder Output

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

encoder construction
Encoder Construction

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

incremental encoder construction
Incremental Encoder Construction

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

gray encoderconstruction
Gray EncoderConstruction

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

transformer based displacement sensors
Transformer Based Displacement Sensors
  • Linear Variable Differential Transformer
  • Synchro’s and Resolvers

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

linear variable differential transformer
Linear Variable Differential Transformer

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

coil voltages
Coil Voltages

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

coils in series opposition
Coils in Series Opposition

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

lvdt animation
LVDT Animation

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

coil voltages22
Coil Voltages

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

amplitude versus displacement
Amplitude versus Displacement

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

output of an lvdt
Output of an LVDT
  • Starting at the primary or excitation side of the LVDT:

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

signal conditioning scheme
Signal conditioning Scheme

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

signal conditioning of a lvdt 1
Signal Conditioning of a LVDT (1)
  • Location of the displacementtransducer coil
    • consider the phase of the output
    • as well as the magnitude
  • Theoutput phase of the position sensor is compared with theexcitation phase and it can be:
    • In or out of phase with theexcitation, depending upon which half of the coil the center ofthe armature is in

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

signal conditioning of a lvdt 2
Signal Conditioning of a LVDT (2)
  • This type of signal conditioning systems is available in IC form.
  • The Analog Devices type AD 598 IC uses this technique.

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

principle of a resolver
Principle of a Resolver

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver operation principle 1
Resolver Operation Principle (1)
  • The rotor of the resolver is exited by an ACreference voltage of 400 Hz typically
  • As the rotor turns and thestator remains static an angular difference in orientation betweenrotor and stator develops:
    • va=Kvexitesinωtsinθ
    • vb=Kvexitesinωt cosθ
  • The shaft angle θ is obtained by first multiplying theoriginal output signals by cosφ and sinφrespectively

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver detector system
Resolver Detector System

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver operation principle 2
Resolver Operation Principle (2)
  • Kvsinωtsinθcosφ and Kvsinωt cosθcosφ
  • Subtractinggives: Kvsinωt sin(θ-φ)
  • (θ-φ) is the angular error
  • Demodulated gives: A sin(θ-φ)
  • Signalto a phase sensitive detectorfollowed by an integrator and a Voltage Controlled Oscillator (VCO)
  • Detection of angle θ is based on nulling the error angle (θ-φ)

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver detector system32
Resolver Detector System

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver operation principle 3
Resolver Operation Principle (3)
  • The VCO controls an up/down counter containingthe digital equivalent of angle θ
  • The whole manipulation isperformed in closed loop fashion
  • Since the difference between θ and φ is nulled, theup/down counter supplies θ
  • In practice allcalculations are performed on--chip such as the AD2S90 from AnalogDevices

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver detector system34
Resolver Detector System

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

excitation and read out chipset
Excitation and Read-Out Chipset

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

principle of a synchro
Principle of a Synchro

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

application of displacement sensors 1
Application of Displacement Sensors (1)
  • Application ofLVDT's
    • On SOHO the LASCO experiment is flown
    • The device requires very accurate positioning measurement. This accurate position measurement isobtained by applying LVDT's
    • The LVDT's were able to measure with aresolution of  0.01 μm over a range of  30 m
  • An other experiment on board of SOHO, the SUMER EUVSpectrometer also applies a LVDT for linearposition measurement. This sensor has aresolution of 12 bits

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

lasco
LASCO

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

soho lasco experiment
SOHO-LASCO Experiment

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

soho lasco experiment40
SOHO-LASCO Experiment

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

soho lasco lvdt characteristics
SOHO LASCO LVDT Characteristics

Stroke in micrometers

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

application of displacement sensors 2
Application of Displacement Sensors (2)
  • Application of Resistive Encoders
    • The CAPS instrument on the Cassini spacecraftisequipped with a resistive encoder to measure the angular positionof the instrument

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

application of displacement sensors 3
Application of Displacement Sensors (3)
  • Application of Optical Encoders:
    • In the pointing and scanning mechanism for ATLID and SPOT5 anoptical encoder is applied to obtained angularposition. The resolution is 21 bits,its static accuracy is 15 μ rad and its bandwidth is a fewhundred Hz
    • For angular position measurement of a tether reel use of an incremental encoder generates 4000 pulses per revolution on two channels in quadrature.
    • In the scan mechanism for the Master Limb SoundingInstrument it is proposed to measure the angle ofthe elevation axis with an incremental encoder

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

application of displacement sensors 4
Application of Displacement Sensors (4)
  • Scanning mechanism of the MIPASInterferometer on board ENVISAT an incremental encoder isused. The outer diameter of the encoder is 182 mm containing 18000equally spaced lines. The accuracy is 1 arcsec
  • An 21 bits optical encoder is applied in a pointingmechanism for a Earth Observation Satellite. The resolution is 3μrad, precision over a range of 3600 is better than 15 μrad
  • The scan mechanism of the Atmospheric LidarInstrument makes use of an encoder
  • In the scanning mechanism for SPOT5a high resolutionpointing and scanning mechanism was required. The encoder applied had 21 bit resolution

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

encoder
Encoder

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

application of displacement sensors 5
Application of Displacement Sensors (5)
  • Resolver Applications
    • The Infrared Atmospheric Sounder Interferometer contains the IASI instrument. Part of theinstrument is a scan sub-system for a mirror. The shaft angle ismeasured by a Resolver
      • The resolver assembly accuracy is 10-4 rad
    • The Global Ozone Scan Monitoring Experimentalso contains a resolver
      • Accuracy is 10 arcsec
    • European Robotic Arm (ERA) is equipped with a 6040 Rotasyn

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

resolver
Resolver

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors

rotasyn resolver
Rotasyn Resolver

Dr. ir. W. Jongkind

AE4-S02 Spacecraft Mechatronics

Displacement Sensors