Design of a Low Cost and Robust Linkage Position Sensing System

1. Design of a Low Cost and Robust Linkage Position Sensing System Phillip Latka & Leann Vernon Dr. Sanchez and Mr. Schmidt May 1st, 2014

2. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Conclusions • Project Summary

3. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Conclusions • Project Summary

4. Project Overview • End Implement Location • D8 • System Types • Linkage Position System • Implement Position System

5. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Conclusions • Project Summary

6. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Conclusions • Project Summary

7. Design Requirements • Cost • Includes: Cost of sensor, manufacturing, and installation costs • Benchmark cost based on CAT’s current system: $1,000-$1,500 • Robustness/Reliability • Vibration 8 g • Environmental Conditions • Potential for 10,000 operating hours • Accuracy • Location of Linkage: 0.1 mm • Location of End Implement: 12.7 mm

8. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Conclusions • Project Summary

9. System Specifications • Output of sensor system • PWM signal • Low current ~3.8 mA • Up to 5 V • Frequency range 0.1 Hz to 12.8 Hz • Duty cycle: 3-97%

10. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Recommendation • Project Summary

11. Design Process • Research Stage • Brainstorming Stage • Initial Brainstorming Phase • General Elimination Phase • Selection Stage

12. Outline • Project Overview • System Overview • Design Requirements • System Specifications • Design Process • Final Designs • Project Recommendation • Project Summary

13. Final Designs • Wheel and Encoder • Laser Distance System (LDS)

14. Final Designs • Wheel and Encoder • Laser Distance System(LDS)

15. Wheel and Encoder • Theoretical Design • Physical Design • Testing Results

16. Wheel and Encoder • Theoretical Design • Physical Design • Testing Results

17. Theoretical Design • Three wheels, protected by a “collar” • Measures the linear displacement of the cylinder rod. • Modular design • Easier maintenance and repair. • Multiple Sensors • Built in redundancy • Increased useful life • Improved accuracy Figure 1: Bottom mounted design Figure 2: Side mounted design

18. Wheel and Encoder • Theoretical Design • Physical Design • Testing Results

19. Physical Design • Collar is attached to cylinder housing • Encoders measure the rotation of the wheel • Wipers keep debris out of the collar • Wheels are slightly compressed against the cylinder rod • Increases friction between the two surfaces. • Minimizes wheel slip Figure 3: System mounting location

20. Wheel and Encoder • Theoretical Design • Physical Design • Testing Results

21. Testing Results • Version 1: • Proof of concept • Two wheel design • Measured displacement within +/- 10mm. • Error caused by tolerance stack ups and missed “pulses” • Version 2: • New absolute encoders • Three wheel design • Much higher tolerances and higher quality absolute encoders. • Average 0.4 mm over ~200 mm Figure 4: Version 1 prototype Figure 5: Version 2 prototype

22. Final Designs • Wheel and Encoder • Laser Distance System(LDS)

23. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

24. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

25. LDS Specs • Operating Voltage: 5 V • LDS Output • Voltage level: 3.3 V • One Full Revolution • 360˚ • 90 Serial Packets, 22 bytes each

26. LDS Specs: Serial Packets Start Byte

27. LDS Specs: Serial Packets Packet Number

28. LDS Specs: Serial Packets LDS Motor Speed

29. LDS Specs: Serial Packets Distance Four Distance Readings

30. LDS Specs: Serial Packets Check Sum

31. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

32. Microcontroller Selection: Requirements • 2 PWM outputs • 2 16-bit Timers • Originally spec’d for operation of a single LDS • PWM module would be beneficial • Serial Inputs • Serial Output of LDS • Voltage level: 3.3 V • Operating voltage: 5 V • Memory • Calibration • Small amount of non volatile RAM • High Computational Ability

33. Microcontroller Selection: Selection • Tiva-C by Texas Instruments • 32-bit ARM for advanced computation • Provides conversion between floating and fixed point • SSI, I2C, and UART interfaces • Two PWM modules • Controlled by 16-, 32-, or 64- bit clock • Supply Voltage 0-4 V • Input Voltage -0.3 to 5.5 V

34. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

35. Hardware Design • Voltage Regulator • Reason: Supply 5V to LDS • Regulator used: 7805 • Motor Control • npn transistor • Surge protection Figure 6: Voltage Regulator 1.7 kΩ Figure 7: Motor Control Circuit

36. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

37. Implementation Design • Two units mounted on side of cab • Scan ± 45º in vertical plane • Each unit identifies two unique points • Four points used to generate a plane for analysis

38. Laser Distance System (LDS) • LDS Specs • Microcontroller Selection • Hardware Design • Implementation Design • Coding Tasks • Testing Results

39. Coding Tasks • LDS Interfacing • UART Interfacing • Tracking Algorithm • Distance Algorithm • PWM Generation

40. Coding Tasks • LDS Interfacing • UART Interfacing • Tracking Algorithm • Distance Algorithm • PWM Generation

41. LDS Interfacing • Voltage regulator circuit to power LDS • Serial connection between LDS and Tiva • Serial connection between Tiva and computer • Motor powered at 3.3V

42. Coding Tasks • LDS Interfacing • UART Interfacing • Tracking Algorithm • Distance Algorithm • PWM Generation

43. UART Interfacing • Serial packets are sent to Tiva through port PB0 • 360 four-byte distances are converted and stored as array of millimeter values • Two-byte motor speed is converted and stored as integer • Millimeter distances are output to computer via serial USB connection and to distance algorithm • Motor speed is output to motor control algorithm

44. Coding Tasks • LDS Interfacing • UART Interfacing • Tracking Algorithm • Distance Algorithm • PWM Generation

45. Tracking Algorithm • Each unit finds two unique points on the blade • Based on blade type • Large cavities or extensions

46. Coding Tasks • LDS Interfacing • UART Interfacing • Tracking Algorithm • Distance Algorithm • PWM Generation

47. Distance Algorithm • Two specific points will be tracked on the blade by each LDS • Each point gives a distance d and angle θ • The four points can be combined to generate a plane for analysis • Resulting Variables • θT: Tilt angle of the Blade • θR: Rotational angle of the Blade • dTL: Distance of Tip to LDS (reference point) • dTG: Distance of Tip to Ground ϴT ϴR

48. Distance Algorithm: Two Dimensional Representation Y (to sky) from LDS 1 P11 P12 d12 d11 from LDS 2 P21 d21 P22 d22 Θ22 X (to blade)

49. Distance Algorithm: Two Dimensional Representation Y (to sky) P11 θT φc P12 d12 d11 P21 d21 P22 d22 Θ22 X (to blade)

50. Distance Algorithm: Two Dimensional Representation Y (to sky) P11 θT φc P12 d12 BH d11 P21 d21 Tip of Blade P22 d22 Θ22 X (to blade)