1 / 46

Electronic Bench Press Spotter

Electronic Bench Press Spotter. ECE 345 – Senior Design Jon Donenberg, Barry Horwitz. Summary. 4 Major Areas of Inquiry Concept Original Design Scale-model Implementation Testing and Analysis Successes, Challenges, and Recommendations. Concept. Description of Problem.

kory
Télécharger la présentation

Electronic Bench Press Spotter

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electronic Bench Press Spotter ECE 345 – Senior Design Jon Donenberg, Barry Horwitz

  2. Summary • 4 Major Areas of Inquiry • Concept • Original Design • Scale-model Implementation • Testing and Analysis • Successes, Challenges, and Recommendations

  3. Concept

  4. Description of Problem • Weightlifters work near maximum lifting ability to promote muscle development • Can be dangerous when the weightlifter reaches muscle ‘failure’ if a system to relieve him or her of the bulk of the weight is not present • Task usually fulfilled by another weightlifter – a ‘spotter’ • Can design an electronic system to fulfill this role

  5. Performance Benchmarks • Speed • typical weightlifters lift in the speed range of 1cm/s to 4 cm/s • Falling weight may approach 1 m/s • Detection Accuracy • eliminate input signal errors • Safety • electrical and mechanical failsafes must ensure a robust device that will not cause injury (and/or lawsuits)

  6. Original Design

  7. Original Design • Full-scale Bench Press System • 200+lbs capacity • Requires kW of power capacity • DC motors rated for such work can run in the thousands of dollars • Financially infeasible (would break the 345 bank) • Decided instead on 1/5 scale model with reduced weight • Operational elements of circuitry are the same; only motor size and controller specs change

  8. Original Design – Input Circuit • Originally based on old sensor array using reflection instead of direct IR signal • Each sensor output is logic LO unless the bar is in front reflecting the beam • In this manner, the sensors were fed to 8-3 Priority Encoders • Four 3-bit strings fed to two 4-bit full adders (most significant bit a function of encoder outputs) • Sensor info added to produce a 5-bit output string

  9. Original Design – Input Circuit • Problems • Sensor reflection based on ideas of ECE110 project lab; not optimal for our project • Original Encoders (MC10165) output logic LO @ 3.5V; attempted using comparators to lower the level to zero proved useless (even Mark couldn't figure it out) • Solution • changing the sensor location to direct beam would necessitate inverters on each input; or a new circuit design • new circuit design more simple, using OR gates

  10. Original Design – Output Circuit • Originally planned to use a smaller motor controller limited to 3A, LMD18200 chip • Problem • After testing the motor with our system, we needed a controller rated for higher currents • Solution • Devantech MD03 – Up to 20A continuous current

  11. Implementation

  12. Input Circuitry – IR Sensor Array • Maximum Detector Characteristics: • Emitter-Collector Voltage: 5V • Ic Collector Current: 50mA • Power Dissipation: 150mW • Peak Sensitivity Wavelength: 850nm • Bandwidth Range: 620-890nm • Angle of half-sensitivity: +/-20o • Maximum Emitter Characteristics: • Continuous Forward Current: 150mA • Radiant Power Output: 15mW • Peak Emission Wavelength: 950nm

  13. Input Circuitry – IR Sensor Array • Emitter-Detector Circuit • Emitter and Detector on ‘line of sight’ • Detector output reads logic HI unless the emitter IR signal is blocked

  14. Input Circuitry – IR Sensor Array • Emitter & Detector Arrays • Measured Total Detector Current: ~200mA • Total Emitter Current: ~100mA

  15. Input Circuitry – Binary Encoder • 32 Bit Priority Encoder • 5-bit string output is sent to Basic-X to designate location of bar within the sensor array

  16. Input Circuitry – Binary Encoder • 3 Levels • Typical Propagation Delays • NAND gates – 125 ns • 83 Encoders – 10ns • Inverters – 20ns • Maximum Propagation Delays • NAND gates – 250ns • 83 Encoders – 15ns • Inverters – 33ns • Total System Maximum Delay ~0.3us

  17. Processing Circuitry – BasicX-24 • BasicX Characteristics: • Program Execution Speed: 16 us/16-bit ADD • Operating Voltage: 5.0V • Current Requirements: 20 mA • Maximum Current (w/ loads): 80mA • Onboard Timer Speed: 512 Hz

  18. Processing Circuitry – Code • Major Executable Functions • Main() – primary executable function; runs at startup • Initialize() – set all variables to initial values • InputValue() – check and identify sensor input • InitializePWM() – turn on internal PWM at specified operating frequency • PutPinPWM() – toggle PWM high/low according to an input duty cycle • CheckInput() – process sensor input and determine the current output state

  19. Processing Circuitry – Code • Output State Sub-Functions • Embedded in CheckInput(), UpCode(), and DownCode() • Reversal Compensation – Pulls bar to top of system and holds it in place until the user is ready to begin lifting again • UpCoil – Coils lift cord as bar is raised • Velocity Compensation – Applies counterforce to get user back to the set minimum velocity • Stuck  Bump Compensation – Applies a slight upward force to the bar when the user is frozen in place for more than 4 seconds

  20. Processing Circuitry – Code • Basic PWM Implementation: • Turn on PWM at 14.456 kHz • Calculate Duty Cycle • Apply Duty Cycle to PWM output (applied within a loop architecture) • Set Duty Cycle to non-operational value • Code Skeleton: Do While (Execution Condition == True) DutyCycle = Operational Value Call PutPinPWM(PinOC1A, DutyCycle) Update Execution Condition Loop DutyCycle = non-operational Value Call PutPinPWM(PinOC1A, DutyCycle)

  21. Processing Circuitry – Code • Velocity Compensation • System subject to a minimum lifting velocity (default = 3 cm/s = 2 sensor lengths per second) • If user falls below minimum velocity, system applies a counterforce to the bar equal and opposite to the amount of force required to raise the velocity back up to 3 cm/s

  22. Processing Circuitry – Code • Velocity Compensation • Acceleration = 9.81 m/s2 + (Vminimum2 – Vactual2)/(2*min. sensor resolution) • Trequired = (mass)*(acceleration)*(pulley radius) • Trequired/TFL = Vrequired/VFL • PWM Duty Cycle = Trequired/TFL TFL, VFL are characteristics of the motor

  23. Output Circuitry – Motor Controller • Devantech MD03 – 50-Volt 20-Amp H-Bridge Motor Driver • Voltage - 5v logic supply and 5V – 50V for the motor • Current - 50mA Max for logic and up to 20a for the motor • Mode 2 - 0v-5v (or PWM equivalent) with separate direction control • Current Limiter – Preset to 20 A

  24. Output Circuitry – Motor Controller www.owlnet.rice.edu/~elec201/ Book/hardware.html

  25. System Mechanical Characteristics • Vertical Sliders • Track Length – 18 in. • Operating Mass • Bar Weight: 632.0 g • Slider Weight: X2 = 457.4 g • Supplemental Mass Weight: X2 = 1281.6 g • Sensor Array • Array Lengths – 0.4 m • Sensor Spacing – 1.5 cm • Pulley Radius – 1 cm

  26. Output Circuitry -- Motor • Motor Sizing: Power requirements • Pmax = (mass)*(gravity acceleration)*(min. sensor resolution)/(min. time resolution) = m*g*(max system velocity) = 94.3463W • Motor Sizing: Current requirements • Imax = Pmax/(Operative Voltage) = 7.86A

  27. Output Circuitry -- Motor • Motor Sizing: Torque requirements • Max acceleration = 9.81 m/s2 + (Vminimum2)/(2*min. sensor resolution) • Tmax = (mass)*(max acceleration)*(pulley radius) = 0.2317 N-m • Motor Sizing: Speed requirements • Pull-up Speed Vup = 1 m/s = 954.9 rpm

  28. Output Circuitry -- Motor • Motor Characteristics: • Model Type: 4z144 • Operating Voltage: 12V • Full Load Torque: 0.2892N-m • Maximum Speed: 1750 rpm • Rated Current: 6.9A-8.1A • Peak Current: 17.5A • Rated Power: 53.29 W • Peak Power: 124.3 W http://www.raemotors.com/pdf/4Z144-143-529-141-140-528-1Z840-842-851%20motor%20only.pdf

  29. Testing

  30. Performance Benchmarks • Speed Analysis • Minimum speed resolution for microprocessor: • 4.1 m/s >> 1m/s • Four orders of magnitude better than necessary

  31. Performance Benchmarks • Speed Analysis • Optimal operating speed ~ 3cm/s • Sensor reads continue through our entire testing range

  32. Performance Benchmarks • Detection Accuracy & Safety • Glitch frequency increases as velocity decreases due to misreads when no sensor is being tripped • How to fix the problem?

  33. Performance Benchmarks • Detection Accuracy & Safety • When no sensor is being tripped, input signal will read 0 or a much lower sensor due to propagation delays in input changes • While moving upward, the next sensor should be above the current sensor • While moving downward, the next sensor should be below the current sensor • Experimental results show that skipping more than three sensors is extremely unlikely • Solution – software error buffers

  34. Performance Benchmarks If (moving upward) then ' error check If (current sensor greater than last sensor) then If (difference between current sensor and read sensor < 2) then If (previously moving downward) then upErrorBuffer = 1 'turn on error buffer End If If (previously moving upward) then If (error buffer is active) then increment error buffer End If If (upErrorBuffer = 2) then Debug.Print "UP "; cstr(Alast); "->"; cstr(A) upErrorBuffer = 0 Call upCode() ElseIf (upErrorBuffer = 0) then Debug.Print "UP "; cstr(Alast); "->"; cstr(A) Call upCode() End If End If prevState = 1 downErrorBuffer = 0 End If End If End If

  35. Performance Benchmarks • Detection Accuracy & Safety • Error checking virtually eliminates glitches except at excessive speeds • Safety is guaranteed at normal operational speeds

  36. Performance Benchmarks • Electromechanical Safety • Operational Currents for reversal trials well within safe range for motor • Mechanical stop included

  37. Successes, Challenges, and Recommendations

  38. Successes • With error checking, system glitches were virtually eliminated • Operational currents fall well within suggested parameters • Prototype model performs to specifications

  39. Challenges • Input Circuit Design and Implementation • Early misunderstanding of power requirements caused scrapping of original output circuit configuration and the death of a few unfortunate capacitors

  40. Challenges • Occasionally sluggish response time at startup (from bottom) due to spikes in current requirements – in the worst case could cause operational failure • Potential Solution: “Stiffening Capacitor” • Used in cars with large sound amplification systems • Capacitor is placed in parallel with motor; charged to the operating voltage (12V) • Capacitor can be used to stabilize voltage level at the motor and dump excess current into the motor when peak exceeds power source ratings • Similar to a low-pass filter; voltage drop is an ‘AC wave’ that is filtered out • (Thanks to Prof. Swenson for insight on this topic!)

  41. Recommendations • How does model scale to full-size, home use? • Need to run a much larger motor – 90V DC off wall AC current is typical • Power requirements to operate on 300lb load ~ 4 kW; at 90V current setup would require ~50A! • Must reduce current requirements

  42. Recommendations • OPTION 1: CAR BATTERY + GEAR BOX • Gear box can be used to step down required torque and reduce current requirements • Tradeoff with maximum operative speed is acceptable due to the relatively low-speed nature of the application • 48V battery with 400 Amp-hrs would likely last for months since motor runs for very short periods of time

  43. Recommendations • OPTION 2: WALL SOURCE + STIFFENING CAPACITOR • Wall source can run 90V motor • Most home fuses are ~20A • Could use large stiffening capacitor to handle brief, peak current requirements • Can also use a gear box in this implementation to reduce current requirements

  44. Recommendations • WORD OF CAUTION: • Capacitor size requirements can be massive • Rule of thumb – 1F/kW of required power • Scale model application requires ~ 0.1 F Capacitor • ~4F for full-scale operation • These things are huge! • If this guy explodes, you may lose your house http://www.sounddomain.com/sku/ROCCPCC40

  45. Special Thanks to: • Mark Weigert • Scott McDonald (and the rest of the machine shop) • Profs. Swenson & Carney • Greg Sorenson • Coffee

More Related