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STABLE. Preliminary Design Review October 18 th , 2012 William Brown Phillip Chen Eric Huckenpahler Laura Hughes Brian Ibeling Chris Johnson. Stabilization Table for Accurately Balancing a Loose Element. Presentation Overview. System Overview Subsystems Sensors Control
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STABLE Preliminary Design Review October 18th, 2012 William Brown Phillip Chen Eric Huckenpahler Laura Hughes Brian Ibeling Chris Johnson Stabilization Table for Accurately Balancing a Loose Element
Presentation Overview • System Overview • Subsystems • Sensors • Control • Motor/Mechanical • Power • User Interface (UI) • Team Roles • Risks and Mitigations • Schedule • Budget
System Objectives • Maintain Desired Ball Position • Knowledge of desired ball position • Knowledge of current ball position • Ability to move ball to desired position • Ball Control • Counter-act forces exerted on ball • Follow desired user input path • User capable to set desired ball position • Unique and Engaging User Experience • Games • Artistic Application
Sensor Subsystem Control System Position Ball Velocity
Requirements & Purpose • Purpose: • Provide the Control Subsystem with time critical data • Needed Information • Gather Ball Position Data • Calculate Ball Velocity Data • Necessary Traits • High Speed • High Accuracy • High Precision • Large Size • Cost, under $300
Sensor Method: Resistive Touch Screen • Pros: • Simplicity • High resolution in range of 1024x1024 to 4096x4096 (for a 24” by 24” screen that is 170 bits per inch resolution) • Linearity < 1.5% (acceptable) • Price <$100 • Wide range of ball options, just need to be heavy • Nice output format: easier to interface • Cons: • Resistive sensors can be noisy • Cracks are fatal
Sensor Method:Capacitive Touch Screen • Pros: • High Accuracy, 99% of true precision • High Resolution 1024x1024 (for a 24” by 24” screen that is 42bits per inch resolution) • Linearity < 1.5% (acceptable) • Less noisy • Highly Durable • Cons: • Restrictive ball type • More complex to interface directly • Price < $300
First Implementation Choice • Resistive Touch Screen • Necessary Hardware to implement: • Dependent on touch screen purchased, some will include a controller that can output RS232 data requiring a MAX232 IC to convert voltage levels to UART acceptable levels. • Others will require a touch screen controller, AR1000 series IC that can directly output UART, I2C or SPI.
Generating Velocity Data • You can’t just sense velocity, it depends on time • Use a timed interrupt to gather position data and save a running average for its velocity. • Frequency at which velocity data will be available TBD (dependent on Control Subsystem’s needs) Acquired Position Data Timer Timer Length
Control SubsystemGeneral outline of surrounding elements Table Control Subsystem Tilt Angle Control Subsystem User Interface Subsystem Sensor Subsystem Position & Velocity
Control Subsystem Properties • Settling time (movement within 0.5mm of desired position) of 5 seconds. • Maximum overshoot of around 2 cm (4%).
Free Body Diagram Drawing and force vectors not to scale Fn Fr Fg Free body diagram of the ball rolling in one dimension
Mass-spring-damper 1D Model External force (Force of gravity along the plate) U = M*g*sin(θ) Ball of mass M Model rolling friction as a damper x B Wall M U
Solving for Proportional Control Root Locus • and substituting for U (to linearize). • Transfer function: • Mass: assume the ball’s mass will be around 0.3 kg. • Damper: the damper represents the force of rolling friction, which is small (, where N is the normal force and Crr 0.003). B 0.008.
Root Locus Analysis (Proportional control) • Proportional control doesn’t yield a desirable transient behavior in the theoretical plant. • This can be seen by the poles being close to the imaginary axis in the Root Locus graph. Increasing the proportional control parameter drives the system to have more oscillatory behavior. • Must start a lead-lag design for controller’s transfer function. • The lag portion is unnecessary, as the function already has step tracking due to the naked integrator.
Root Locus Setup (Lead Component) • Desires: • to place a closed loop zero very far to the left to allow for poles to move further left (thereby becoming more stable). • to then place a closed loop pole even further to the right to minimize its effect on the system. • , where K is the root locus parameter.
Root Locus Analysis of Lead-Lag Controller • Choosing and , we arrive at a step response with an overshoot of 4% and a settling time of essentially 0.02 seconds • Problems • This model assumes we can actuate the plate instantaneously, when in reality the motor setup will respond much more slowly. • We have approximated the sine function, which may lead to more overshoot.
Requirements & Purpose • Purpose: • Actuate the plate according to instructions from the Control system • Needed Information • Desired position of each axis independently, relative to current position
Footer Text Restrictions • High Speed • High Accuracy • Preferably smaller and non-conducting • Cost, including replacements
DC Brushed Basics: When the motor windings become energized, a temporary magnetic field is created that repels(and/or attracts) against permanent magnets. This force is converted into shaft rotation, which allows the motor to do work. As the shaft rotates, electric current is routed to different sets of windings, maintaining electromotive repulsion/attraction, forcing the rotor to continually turn. Pros: • Cost. Cheaper than stepper or servo motors • Super easy to work. Connect one wire high, one low, watch it go! Cons: • Torque vs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. • Can be electrically noisy and could interfere with the uC or any wireless network we set up. • A physical commentator is going to eventually wear out. New motor = new calibration process.
DC Brushed Basics: When the motor windings become energized, a temporary magnetic field is created that repels(and/or attracts) against permanent magnets. This force is converted into shaft rotation, which allows the motor to do work. As the shaft rotates, electric current is routed to different sets of windings, maintaining electromotive repulsion/attraction, forcing the rotor to continually turn. Pros: • Cost. Cheaper than stepper or servo motors • Super easy to work. Connect one wire high, one low, watch it go! Cons: • Torque vs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. • Can be electrically noisy and could interfere with the uC or any wireless network we set up. • A physical commentator is going to eventually wear out. New motor = new calibration process.
DC Brushed Basics: When the motor windings become energized, a temporary magnetic field is created that repels(and/or attracts) against permanent magnets. This force is converted into shaft rotation, which allows the motor to do work. As the shaft rotates, electric current is routed to different sets of windings, maintaining electromotive repulsion/attraction, forcing the rotor to continually turn. Pros: • Cost. Cheaper than stepper or servo motors • Super easy to work. Connect one wire high, one low, watch it go! Cons: • Torque vs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. • Can be electrically noisy and could interfere with the uC or any wireless network we set up. • A physical commentator is going to eventually wear out. New motor = new calibration process.
DC Brushed Basics: When the motor windings become energized, a temporary magnetic field is created that repels(and/or attracts) against permanent magnets. This force is converted into shaft rotation, which allows the motor to do work. As the shaft rotates, electric current is routed to different sets of windings, maintaining electromotive repulsion/attraction, forcing the rotor to continually turn. Pros: • Cost. Cheaper than stepper or servo motors • Super easy to work. Connect one wire high, one low, watch it go! Cons: • Torquevs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. • Can be electrically noisy and could interfere with the uC or any wireless network we set up. • A physical commentator is going to eventually wear out. New motor = new calibration process.
DC Brushless Basics: Same as brushed, but the commutator is realized with a switch. The field inside a brushless motor is switched via an amplifier triggered by a commutating device, such as an optical encoder. Pros: • Cost. Cheaper than stepper or servo motors. • Won’t wear out nearly as quickly as a brushed motor. • Fewer physical parts means fewer factors that carry their own mess of randomization. • Cyprus has a great dev kit and software suite for $99 that we could play with (proof of concept) • I know how to keep these from breaking things by limiting the torque. Cons: • Torque vs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. However, because it is essentially PWM controlled, it’s going to be easier than brushed. • Can be electrically noisy and could interfere with the uC or any wireless network we set up.
DC Brushless Basics: Same as brushed, but the commutator is realized with a switch. The field inside a brushless motor is switched via an amplifier triggered by a commutating device, such as an optical encoder. Pros: • Cost. Cheaper than stepper or servo motors. • Won’t wear out nearly as quickly as a brushed motor. • Fewer physical parts means fewer factors that carry their own mess of randomization. • Cyprus has a great dev kit and software suite for $99 that we could play with (proof of concept) • I know how to keep these from breaking things by limiting the torque. Cons: • Torque vs Size. Many of these will be for smaller hobby applications and it’s hard to find a low RPM, high torque DC motor in a smallish package. • Accuracy. It’s going to be pretty hard to calibrate this, and that could change with differences in load like a different ball. However, because it is essentially PWM controlled, it’s going to be easier than brushed. • Can be electrically noisy and could interfere with the uC or any wireless network we set up.
Stepper Basics: Takes input from a uC to move in precise, accurate, pre-determined steps. Pros: • Easier to code for b/c based on simple integer values • Higher chance of startup jerk than DC motors, but we actually might want that to negate static friction Cons: • Accuracy. Even with 200 steps/rotation (typical) moving a single step would tilt the edge of the plate 9*arcsin(1.8deg) or about 1/3”. This could be good enough, but we may run into a maximum update rate depending on our controller. • Cost. Somewhat more expensive than DC motors.
Stepper Basics: Takes input from a uC to move in precise, accurate, pre-determined steps. Pros: • Easier to code for b/c based on simple integer values • Higher chance of startup jerk than DC motors, but we actually might want that to negate static friction Cons: • Accuracy. Even with 200 steps/rotation (typical) moving a single step would tilt the edge of the plate 9*arcsin(1.8deg) or about 1/3”. This could be good enough, but we may run into a maximum update rate depending on our controller. • Cost. Somewhat more expensive than DC motors.
Stepper Basics: Takes input from a uC to move in precise, accurate, pre-determined steps. Pros: • Easier to code for b/c based on simple integer values • Higher chance of startup jerk than DC motors, but we actually might want that to negate static friction of the ball Cons: • Accuracy. Even with 200 steps/rotation (typical) moving a single step would tilt the edge of the plate 9*arcsin(1.8deg) or about 1/3”. This could be good enough, but we may run into a maximum update rate depending on our controller. • Cost. Somewhat more expensive than DC motors.
Voice Coils Basics: Voice coils use a magnetic field to push a metal piston up and down. Pros: • The cool factor • High precision and extremely fast Cons: • Range. They are designed more for small vibration control than ball-catching angles. The best we can get is about 1” of lift. • We would be fighting gravity instead of working with it. • Calibration would need to be ongoing and the plate would need to consciously return to a level state. • More difficult to discretely control.
Voice Coils Basics: Voice coils use a magnetic field to push a metal piston up and down. Pros: • The cool factor • High precision and extremely fast Cons: • Range. They are designed more for small vibration control than ball-catching angles. The best we can get is about 1” of lift. • We would be fighting gravity instead of working with it. • Calibration would need to be ongoing and the plate would need to consciously return to a level state. • More difficult to discretely control.
Voice Coils Basics: Voice coils use a magnetic field to push a metal piston up and down. Pros: • The cool factor • High precision and extremely fast Cons: • Range. They are designed more for small vibration control than ball-catching angles. The best we can get is about 1” of lift. • We would be fighting gravity instead of working with it. • Calibration would need to be ongoing and the plate would need to consciously return to a level state. • More difficult to discretely control.
Voice Coils Basics: Voice coils use a magnetic field to push a metal piston up and down. Pros: • The cool factor • High precision and extremely fast Cons: • Range. They are designed more for small vibration control than ball-catching angles. The best we can get is about 1” of lift. • We would be fighting gravity instead of working with it. • Calibration would need to be ongoing and the plate would need to consciously return to a level state. • More difficult to discretely control.
Servo Basics: These are really a subset of other continuous motors, unique only because they have a strict, built in feedback system. Pros: • THE hobbyist motor, so there’s a ton of application specific information out there. • High precision and fast • LEGO makes one, so we should be able to figure it out. Cons: • Accuracy. They could have the same issues as stepper motors or DC, depending on what the servo base is. • Maximum Update rate – as Michael points out, we are going to battle the real-time aspect of this every step of the way. The motors are a bad place to start. • Cost. Built in feedback is apparently pretty expensive. • Size and weight. These are typically much larger than their counterparts.
Servo Basics: These are really a subset of other continuous motors, unique only because they have a strict, built in feedback system. Pros: • THE hobbyist motor, so there’s a ton of application specific information out there. • High precision and fast • LEGO makes one, so we should be able to figure it out. Cons: • Accuracy. They could have the same issues as stepper motors or DC, depending on what the servo base is. • Maximum Update rate – as Michael points out, we are going to battle the real-time aspect of this every step of the way. The motors are a bad place to start. • Cost. Built in feedback is apparently pretty expensive. • Size and weight. These are typically much larger than their counterparts.
Servo Basics: These are really a subset of other continuous motors, unique only because they have a strict, built in feedback system. Pros: • THE hobbyist motor, so there’s a ton of application specific information out there. • High precision and fast • LEGO makes one, so we should be able to figure it out. Cons: • Accuracy. They could have the same issues as stepper motors or DC, depending on what the servo base is. • Maximum Update rate – as Michael points out, we are going to battle the real-time aspect of this every step of the way. The motors are a bad place to start. • Cost. Built in feedback is apparently pretty expensive. • Size and weight. These are typically much larger than their counterparts.
Servo Basics: These are really a subset of other continuous motors, unique only because they have a strict, built in feedback system. Pros: • THE hobbyist motor, so there’s a ton of application specific information out there. • High precision and fast • LEGO makes one, so we should be able to figure it out. Cons: • Accuracy. They could have the same issues as stepper motors or DC, depending on what the servo base is. • Maximum Update rate – as Michael points out, we are going to battle the real-time aspect of this every step of the way. The motors are a bad place to start. • Cost. Built in feedback is apparently pretty expensive. • Size and weight. These are typically much larger than their counterparts.
Servo • 4.8 to 6.0V • Torque around 6kg*cm • Small Footprint • $12 • 180 degrees of movement
Pivot • Work WITH Gravity • Introduce minimal friction • Can limit motion of plate with slant of pivot tip
Contact with Plate • Cannot interfere with resistance or capacitance of plate • Introduce minimal friction • Allow full range of motion • Be easy to implement and repair
Servo + + = proof of concept
Footer Text Power Subsystem
