DIFFERENTIAL POLARIZATION DELAY LINE controller D0215 Supervisor : Mony Orbach Performed by: Maria Terushkin Guy Ovadia Technion – Israel Institute of Technology Department of Electrical Engineering High Speed Digital Systems Lab

Project definition Build a controller for the Differential Delay Line module in the faculty’s EO lab. Precisely determine and control the position of the mirror inside the module. Closed loop positional control using the built in optical shaft encoder for feedback. Create a PC interface through a USB connection.

Project Features Closed-loop motor control (PID algorithm) Closed-loop motor control (PID algorithm) Interface Functions Interface Functions Go to specified position Go to specified position Set zero position Set zero position Read-back of current position Read-back of current position Apply motor break while holding position. Apply motor break while holding position. Slow down gradually near travel limits Slow down gradually near travel limits Built In Tests (discussed later in the presentation) Built In Tests (discussed later in the presentation)

Project Specifications Encoder input Encoder input A, B Channels: 5V TTL (internal 10kΩ resistive pullup). Up to 7.2 kHz A, B Channels: 5V TTL (internal 10kΩ resistive pullup). Up to 7.2 kHz 5V Vcc and Ground (10 mA maximum consumption) 5V Vcc and Ground (10 mA maximum consumption) Limit switches Limit switches Two End-of-travel signals: Open collector, active high. Two End-of-travel signals: Open collector, active high. USB I/O USB I/O Maximum speed: 1 MByte/s (practical throughput is low) Maximum speed: 1 MByte/s (practical throughput is low) Signals: D+, D-, 5V Vcc, Gnd Signals: D+, D-, 5V Vcc, Gnd

Mechanical aspects Method of construction: Wireup card Method of construction: Wireup card Connections to the MMC card: direct soldering Connections to the MMC card: direct soldering Enclosure: pre-made box Enclosure: pre-made box External connectors: External connectors: Power connector Power connector DDL connector DDL connector No heatsinks are required No heatsinks are required

Project Specifications Performance (preliminary requirements) Performance (preliminary requirements) Steady State Positional Error: < 0.5 µm (single encoder step) Steady State Positional Error: < 0.5 µm (single encoder step) Commulative positional error: 0 µm Commulative positional error: 0 µm Overshoot: 25 [%] (non critical, but should be lowered near travel limits). Overshoot: 25 [%] (non critical, but should be lowered near travel limits). Small Step settling time (to 0.5 µm): will be setted on the real model. Small Step settling time (to 0.5 µm): will be setted on the real model. Full travel settling time (to 0.5 µm): will be setted on the real model. Full travel settling time (to 0.5 µm): will be setted on the real model. Limit velocity to +/- 1 [mm/s] Limit velocity to +/- 1 [mm/s]

Block diagram DDL controller PC + simple UI USB Communication Unit Laboratory measurement equipment Fiber optics

DDL – controller diagram Limit Switches DC motor Encoder H-bridge Power supply 12MHz clk FPGA DDL

The chosen H-bridge: HIP4020 Two Independently controlled power Half-Bridges 3-12V operation 0.5A Maximum load CMOS/TTL Compatible Input Logic Over-Temperature Shutdown Protection Over current Limit Protection Over current Fault Flag Output Direction, Braking and PWM Control Manufacturer: Intersil Low cost, available from Farnell

MMC Platform The project is based on a platform previously designed in the HS-DSL. The project is based on a platform previously designed in the HS-DSL. The platform we will use is the Momentum Measurement Card created by Hadas Preminger & Uri Niv. The platform we will use is the Momentum Measurement Card created by Hadas Preminger & Uri Niv.

Project Specifications I/O Signals I/O Signals Input power Input power 9V, 1A wall adapter 9V, 1A wall adapter Typical consumption (motor running): TBD, estimated at 250mA (1.5W) Typical consumption (motor running): TBD, estimated at 250mA (1.5W) Typical consumption (motor idle): TBD, estimated at 50mA ( 0.25 W) Typical consumption (motor idle): TBD, estimated at 50mA ( 0.25 W) Motor output Motor output Fixed frequency PWM signal at 20 kHz Fixed frequency PWM signal at 20 kHz Reversible polarity Reversible polarity 6 V nominal, adjustable by trimpot between 3-8 V for calibration during development (unaccessible to user). 6 V nominal, adjustable by trimpot between 3-8 V for calibration during development (unaccessible to user). 250mA max current (limited by motor resistance) 250mA max current (limited by motor resistance)

Cyclone FPGA Altera’s low cost, simple FPGA 2910 Logic Elements, ~60,000 kBit RAM, clock PLL, >100 I/O pins, JTAG support Suitable for implementing glue logic, MCU function, signal processing and more

Built In Tests Test distance between limit switches: result must be in specific range Test distance between limit switches: result must be in specific range Move forward, then backward by the same amount. Verify that the position is the same Move forward, then backward by the same amount. Verify that the position is the same Move to a specific location. Perform readback of location. Verify that it is the same position. Move to a specific location. Perform readback of location. Verify that it is the same position.

Acceptance Tests All Built In Tests are also acceptance tests All Built In Tests are also acceptance tests Arriving a specified position by a preset time: Arriving a specified position by a preset time: Separate tests for both directions Separate tests for both directions Test for small step (10um), medium step (1000um) and full travel range. Test for small step (10um), medium step (1000um) and full travel range. Holding position: position change while idle is up to 1 encoder count Holding position: position change while idle is up to 1 encoder count Travel near limit switches: measured velocity drops near the limits. Movement stops if limit switch is hit. Travel near limit switches: measured velocity drops near the limits. Movement stops if limit switch is hit.

The model

Two axis motion control mechanism (we use only one stage) Two axis motion control mechanism (we use only one stage) Includes motor, encoder, and limit switches Includes motor, encoder, and limit switches Model can work with the same interface, with minimal adaptations Model can work with the same interface, with minimal adaptations Some parameters will needed to be adjusted separately to the model: Some parameters will needed to be adjusted separately to the model: PID parameters: Ki, Kd, Kp PID parameters: Ki, Kd, Kp Velocity and Acceleration planning adjustment Velocity and Acceleration planning adjustment Supply voltage Supply voltage

Controller type PID algorithms adjust the gain to the plant based on several characteristics of the feedback, not just the current value. The error term is derived by subtracting the feedback (motor position) from the set point (set position). This is the error in terms of a number of encoder counts. Simple proportional coefficient Kp is multiplied by the error term. Provides linear response to the error term. Integral coefficient Ki is multiplied by the error term and added to the sum of all previous integral terms. Provides response to accumulated error. Derivative coefficient Kd is multiplied by the difference between the previous error and the current error. Responds to change in error from one PID cycle to the next.

PID controller - overview PID controller - overview Effects of changes in parameters: Effects of changes in parameters: Parameter Rise Time Overshoot Settling Time S.S.Error Parameter Rise Time Overshoot Settling Time S.S.Error P Decrease Increase Small Change Decrease P Decrease Increase Small Change Decrease I Decrease Increase Increase Eliminate I Decrease Increase Increase Eliminate D Small Change Decrease Decrease Small Change D Small Change Decrease Decrease Small Change Vset Vsensor PIDPID sensor plant amp Vout + - +

Pitfalls of PID Integral windup Integral windup The problem arises when the actuator saturates The problem arises when the actuator saturates There is no longer a linear relation between the controller output to the plant’s reaction There is no longer a linear relation between the controller output to the plant’s reaction When this happens, the integrator sums the large error and reaches a very high value When this happens, the integrator sums the large error and reaches a very high value When the error is finally reduced, it would take a long time for the integrator to “unwind” and fall back to a normal value When the error is finally reduced, it would take a long time for the integrator to “unwind” and fall back to a normal value This is called “Integral Windup”

Commonly used schemes to reduce the effects of integrator windup: Clamp the integrator output. This scheme, simply involves clamping the integrator output at a specified maximum level.

Cont. Stop integration on saturation. This scheme, involves switching off the input to the integrator when the actuator goes into saturation.

Cont. Saturation feedback. This scheme, involves an extra feedback loop reducing the input to integrator in proportion to the saturation error signal.

Tuning the PID controller: The Ziegler-Nichols method The closed loop method prescribes the following procedure: The closed loop method prescribes the following procedure: Step 1: Disable any D and I action of the controller (--> pure P-controller) Step 1: Disable any D and I action of the controller (--> pure P-controller) Step 2: Make a setpoint step test and observe the response Step 2: Make a setpoint step test and observe the response Step 3: Repeat the SP test with increased / decreased controller gain until a stable oscillation is achieved. This gain is called the "ultimate gain" Ku. Step 3: Repeat the SP test with increased / decreased controller gain until a stable oscillation is achieved. This gain is called the "ultimate gain" Ku. Step 4: Read the oscillation period Pu. Step 4: Read the oscillation period Pu. Step 5: Calculate the parameters according to the following formulas: Step 5: Calculate the parameters according to the following formulas: PI: Proportional gain = 0.45 * Ku, integral time =Pu / 1.2 PI: Proportional gain = 0.45 * Ku, integral time =Pu / 1.2 PID: Proportional gain = 0.6 * Ku, integral time =Pu / 2, derivative time = Tu / 8 PID: Proportional gain = 0.6 * Ku, integral time =Pu / 2, derivative time = Tu / 8

An alternative… As an alternative to the table above, another set of tuning values have been determined by Tyreus and Luyblen for PI and PID, often called the TLC tuning rules. These values tend to reduce oscillatory effects and improves robustness. As an alternative to the table above, another set of tuning values have been determined by Tyreus and Luyblen for PI and PID, often called the TLC tuning rules. These values tend to reduce oscillatory effects and improves robustness. Since in our system it is important to avoid oscillatory effects we’ll use this method. Since in our system it is important to avoid oscillatory effects we’ll use this method.

Logic design PID Trajectory Planning Xf M er r Current via point To Tf Tf1 Xf1 Tf2 Xf2 … Tff Xff Yes! End of trajectory Arrived via point – err=0

Milestones Electrical schematics done Electrical schematics done Test system built and tested to satisfy our needs Test system built and tested to satisfy our needs Mechanical design complete Mechanical design complete Logical design of the system finished Logical design of the system finished – system assembled and programmed – system assembled and programmed – preliminary testing on the model done – preliminary testing on the model done – debugging finished – debugging finished PC software written PC software written Controller integrated with the real system Controller integrated with the real system – Design finalized (including enclosure, wiring etc.) – Design finalized (including enclosure, wiring etc.) Integration with the setup at the EO lab Integration with the setup at the EO lab.

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