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Elmo HARmonica Tuning Manual

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Elmo HARmonica
Hands-on Tuning Guide
September 2003

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  • Page 1 Elmo HARmonica Hands-on Tuning Guide September 2003...

  • Page 2: Revision History

    This document is delivered subject to the following conditions and restrictions: This guide contains proprietary information belonging to Elmo Motion Control Ltd. Such information is supplied solely for the purpose of assisting users of the Elmo HARmonica servo drive in tuning the device.

  • Page 3: Table Of Contents

    Contents 1. Introduction ..........................1 2. Tuning Current ........................1 3. Tuning Velocity........................1 Auto-tuning Velocity....................1 3.1.1 Step 1......................... 1 3.1.2 Step 2......................... 2 3.1.3 The Auto-tuning Procedure................3 Manually Tuning Velocity ..................3 3.2.1 Manual Tuning with a Low-pass Filter ............14 3.2.2 Manual Tuning of a PI Controller with a Notch Filter .......17 Advanced Manual Tuning ..................20...

  • Page 5: Introduction

    1. Introduction When a new motor is connected to the HARmonica servo drive, you should use the Composer Wizard to set the motor parameters and to tune the control loops. The Wizard will assist you in choosing the optimal drive parameters, step-by-step.

  • Page 6: Step 2

    Elmo HARmonica Tuning Guide HARTG0903 3.1.2 Step 2 From the Auto Tuning Mode drop-down list: Select Expert tuning for bounded if position boundaries cannot be exceeded. Select Expert tuning for free motion if there is no restriction on the system motion.

  • Page 7: The Auto-Tuning Procedure

    3.1.3 The Auto-tuning Procedure The auto tuning procedure is built on the following steps. The tuner creates a velocity step command and finds a low bandwidth control loop, to enable the motor to move while performing system identification. The tuner injects a current command at different frequencies, while moving the motor at a constant speed.
  • Page 8 Elmo HARmonica Tuning Guide HARTG0903 In the first pane, you can see the Velocity and the Velocity command and in the second, you can see the Current command. If the current command has reached the peak current, reduce the velocity command and repeat the test, multiplying KP by 2.
  • Page 10 Elmo HARmonica Tuning Guide HARTG0903...
  • Page 12 Elmo HARmonica Tuning Guide HARTG0903...
  • Page 13 Here we can see that we have reached a 25% overshoot and the beginning of oscillations. 10. At this point reduce KP to 75% of its value and repeat the test.
  • Page 14 Elmo HARmonica Tuning Guide HARTG0903 We can see that the oscillations have disappeared and the overshoot has been reduced to 10%. 11. At this point, we can add KI to the controller. If one of the phenomena described in step 9 has returned, revert to the previous value of KP.
  • Page 15 In this case, it is 0.0016 sec. 13. Set KI/KP to 1/rise time = 625. KI = (KI/KP) * KP = 75,000 If machine vibrations are dangerous, set KI/KP to 0.5/rise time and increase KI until an undershoot or oscillations occur. 14.
  • Page 16 Elmo HARmonica Tuning Guide HARTG0903 This shows a nice response with no undershoot or oscillations. The system has stabilized after 3.25 msec. 16. Had the KI been too great, oscillations or too large an undershoot would have occurred. To observe this case, increase KI to 90,000.
  • Page 17 In either of these cases, the gain must be reduced to enable a larger system margin. To see this, reduce KP and run the test: 18. Set the following parameters: Rise time = 0.0018 sec KI/KP = 1 / Rise time = 555 KI = 80 * 555 = 44400 We can see we that the resulting settling time is 5.75 msec.

  • Page 18: Manual Tuning With A Low-Pass Filter

    Elmo HARmonica Tuning Guide HARTG0903 3.2.1 Manual Tuning with a Low-pass Filter Going back to KP = 40 and KI = 0 we can see high frequency vibrations in both the Velocity and Current command. Adding a low-pass filter with a high frequency will reduce the RMS noise of the...
  • Page 19 Adding the low-pass filter results in an overshoot at KP = 80. A KP of 100 gives an overshoot of 20% and the beginning of oscillations.
  • Page 20 Elmo HARmonica Tuning Guide HARTG0903 Reducing KP to 75 results in the following performance: Rise time = 0.002 sec results in KI/KP = 500. When adding a low-pass filter, do not set the KI/KP higher than filter frequency.

  • Page 21: Manual Tuning Of A Pi Controller With A Notch Filter

    Set KI = 500 * 75 = 37500. The following performance results: Settling time is 5.5 msec. It is recommended to set a low-pass filter of 600 Hz with a damping of 0.55 at the beginning of each tuning procedure. 3.2.2 Manual Tuning of a PI Controller with a Notch Filter During the design of a PI controller, the designer can conclude from the test results...
  • Page 22 Elmo HARmonica Tuning Guide HARTG0903 In this example the measured speed also exhibits oscillations. In most cases, however, the resonance phenomenon is more clearly identified from the current response than from the speed response. Measure the resonance frequency, that is, how many oscillations appear in a second.
  • Page 23 x 10 -0.6 Speed -1.8 Reference Tim e (sec.) 1.76 1.12 0.48 -0.16 -0.8 Tim e (sec.) Figure 3-3: Test results showing how notch eliminates current oscillations due to mechanical resonance 0.36 0.32 0.28 0.24 0.32 0.34 0.36 0.38 Tim e (sec.) Figure 3-4: Zoom of current test measurement for the same controller used in Figure 3- 2 with notch.

  • Page 24: Advanced Manual Tuning

    Elmo HARmonica Tuning Guide HARTG0903 Repeat the test with different damping values according to the following guideline: Try using the largest damping factor value, which knocks out the resonance. Do not try using damping factors that are too small (0.07 is considered small) because too...
  • Page 25 Reducing the gains to KP = 20, KI = 15000 results in the following performance: In order to gain stability at low velocities, we use gain scheduling and reduce the gains at low speeds. We can see that the KI/KP factor is higher at low speed in order to overcome friction.
  • Page 26 Elmo HARmonica Tuning Guide HARTG0903 First set the Displacement to +/-1000 and the Velocity to 20,000. You will see the last row in the table marked. Uncheck the Gain Scheduling ON and Profiler Mode check boxes. Running a test in this way it exactly the same as running a test in manual tuning.
  • Page 27 Now, reduce the parameters until you get satisfactory results for the steady state velocity. In our case, we saw that KP = 20 and KI = 15000 gave us satisfactory performance. Check the Accept check box on the 505 cnt/sec row and proceed to the next speed.
  • Page 28 Elmo HARmonica Tuning Guide HARTG0903 The results will be: 10. After setting acceptable parameters for each tuned speed and checking Accept in that row, click Interpolate and then check Gain Scheduling ON.

  • Page 29: Tuning Position

    4. Tuning Position 4.1 Introduction According to the following formula, it can be seen that implementing a PI velocity loop resulted in a position controller equivalent to a PID controller with KI = 0; = KI ; KD = KP speed speed ...

  • Page 30: Tuning The Position Loop

    Elmo HARmonica Tuning Guide HARTG0903 This graph shows that the position loop is closed without closing the position constant error. 4.2 Tuning the Position Loop Reduce the velocity KI by half, and set a step in velocity:...
  • Page 31 Set position KP = 0.5/rise time. This will give a position bandwidth that position equals the velocity bandwidth divided by 4. In this case, = 0.5/0.0018 = 280. This results in the following performance: position...
  • Page 32 Elmo HARmonica Tuning Guide HARTG0903...
  • Page 33 To better tuning position loop, complete the Wizard process and then select Tools - Advanced Manual Tuning from the Composer main menu. Click in the toolbar to open the motion monitor and select the following parameters to record: Display 1: Position Error Display 2: Velocity, Velocity command Display 3: Current command Set the Trigger Mode to Auto, the Source to Begin Motion and the Delay to...
  • Page 34 Elmo HARmonica Tuning Guide HARTG0903 Start the recorder and press Run Test. The following graph will be displayed:...
  • Page 35 We would expect an overshoot on the velocity followed by a small undershoot. You may iterate on the KI parameter of the inner loop and on the outer loop parameter KP. The iteration range for the KI of the inner loop should not exceed 50% of its original value, and the iteration on the outer loop should not exceed 100% of its original value.

  • Page 36: Lowering The Speed

    Elmo HARmonica Tuning Guide HARTG0903 10. Increase the position KP to 500 The following performance results: More oscillations are evident. 4.3 Lowering the Speed We can see from the graph that the system vibrates at low and zero speeds. This is due to a delay in the information caused by the sensor at low speed. The velocity loop should not be closed at a bandwidth greater than V/10.
  • Page 37 In practice, KP <=V/5, the velocity KP should be reduced by the same factor as position position KP, and the velocity KI should be reduced by a square of that factor. In our case, KP should not be reduced until 280*5 = 1400 cnt/sec. Copy the parameters of the last row to the entire table by selecting Interpolate All on that row, using the right-button pop-up menu.
  • Page 38 Elmo HARmonica Tuning Guide HARTG0903 1000 cnt/sec (7.5 RPM) 500 cnt/sec (3.75 RPM)
  • Page 39 Check the Accept check box of the tuned velocities and select Interpolate All again. Check the Gain Scheduling ON check box and close the Advanced Manual Tuning dialog box. In order to make the system more rigid, you can increase the GS[10]parameter. In order to make the system more stable at low speeds and at no speed, reduce GS[10].
  • Page 40 Elmo HARmonica Tuning Guide HARTG0903 The position error remains for a log period. Too low a value for GS[10] gives a poor response to external disturbance. Remember to save your application after tuning with the Advanced Manual Tuning option. The application is not saved automatically on exit.

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