SLIDE 1
High Speed/High Resolution Encoder Interface for Sean Graves PhD Visi-Trak Sensors Charlottesville VA
Sean Graves PhD Visi-Trak Sensors Charlottesville VA High - - PowerPoint PPT Presentation
Sean Graves PhD Visi-Trak Sensors Charlottesville VA High - - PowerPoint PPT Presentation
Sean Graves PhD Visi-Trak Sensors Charlottesville VA High Speed/High Resolution Encoder Interface for Overview New linear position/velocity sensor Non-contact High resolution High speed Based on proven
SLIDE 2
SLIDE 3
Principal of Operation
System is composed of
sensor body + encoded rod
Senses motion of rod
with respect to sensor body
Based on existing Visi-
Trak sensor that uses Hall Effect
SLIDE 4
Original sensor: 25 year history
SLIDE 5
Standard Encoder Principle of Operation
Encoded piston rod with chrome plating Non-contact Hall Effect sensor Quadrature output
Classical multiply-by-four approach, which limits resolution to 80 counts/inch with a 20 TPI target
SLIDE 6
Enhanced Sensor
Magnetic sensor uses GMR
effect (Giant Magneto- resistance)
Higher resolution: < .001” Higher speed: > 200 IPS / 5
MPS
Serial data output directly
from sensor
On-board processor (TI
MSP430)
No calibration necessary
SLIDE 7
Not Hall Effect
GMR is a quantum mechanical effect,
discovered in 1988
Nobel Prize 2007 in Physics went to
discoverers
Unrelated to Hall Effect sensors
Benefits: GMR Hall Size Small Small Signal Level Large Small Sensitivity High Low Temperature Stability High Low Power Consumption Low Low Cost Low Low
SLIDE 8
Typical Application
Die casting shot-end velocity
measurement
Harsh
environment
Noise
immunity
SLIDE 9
Enhanced Encoder Principle of Operation
Same rod design as standard encoder Non-contact GMR sensor Patented anti-aliasing algorithm Serial (RS-422) output
Effectively multiplies resolution by 64, providing resolution finer than .001”
SLIDE 10
Enhanced Sensor Anti-aliasing Algorithm
Models the velocity and acceleration Bounds the possible accelerations Able to track analog quadrature outputs
with frequency contents higher than the Nyquist frequency
Algorithm patented by UVA
SLIDE 11
Enhanced sensor
SLIDE 12
Sensor development
SLIDE 13
External signal processor
SLIDE 14
Integrated signal processor
SLIDE 15
Performance Data
Test profile:
20 TPI, 1Khz, V = .65 m/s, A = 661 m/s2
SLIDE 16
Results
Standard algorithm exhibits aliasing
errors at velocity > 0.65 m/s
SLIDE 17
Enhanced algorithm
No aliasing exhibited
SLIDE 18
Linear Position Sensor Options
SLIDE 19
Linear Position Sensor Options
Encoders
Linear Cable actuated
Contact sensors with limited-to-good resolution at low speeds. Miniaturization is mechanically limited.
SLIDE 20
Linear Position Sensor Options
Hall Effect
Non-contact sensors with low cost, but low signal level and sensitivity. Low temperature
- stability. Small physical size.
SLIDE 21
Linear Position Sensor Options
Magnetorestrictive (Anisotropic MR,etc.)
Non-contact sensors with high resolution, low
sampling rate, high cost.
SLIDE 22
Linear Position Sensor Options
Potentiometer
Contact sensors with low cost, but noisy
- utput, non-linearity, prone to mechanical
failure (esp. at high speeds)
SLIDE 23
Linear Position Sensor Options
Capacitive
Non-contact sensors with low cost, high resolution, high linearity. Low temperature stability, limited use in harsh conditions.
SLIDE 24
Linear Position Sensor Options
Linear Variable Differential Transformer
(LVDT)
Non-contact sensors with high resolution,
- reliability. Limited stroke. Some non-linearity/
temperature dependency. High cost.
SLIDE 25
Linear Position Sensor Options
Optical
Non-contact sensors with good resolution. Narrow temperature range, not for harsh environments.
SLIDE 26
Applications
Die casting Injection molding Glass molding Off-highway vehicles Oil/Gas production Military Power generation Entertainment Forest products
SLIDE 27