TUNING ASDA SERIES SERVO SYSTEMS

About This Presentation Intended Audience Basic level, for the users who knows how to operate ASDA series servo systems. Presentation Revision Revision: 1/24/2010 Revision: Rev. 1/21/2010 is abandoned.

Table of Contents The Background Knowledge A Glance of ASDA Series Servo System, Resolution of Encoder, Response, Bandwidth, Stiffness, and Rigidity The Control Skeleton Three Cascaded Loops, Position Control Loop, Speed Control Loop, and Torque Control Loop Scope Skill How to Measure Resonance, Performance Monitoring, and Inertia Evaluation

The Whole ASDA Series

ECMA Servo Motor Rated Torque: 0.32 N-m ~ N-m Max. Torque: 0.96 N-m ~ N-m Rotation Speed: 1000 rpm ~ 5000 rpm Encoder Resolution: 2500 ppr,17 bits, 20 bits The Power Range 0.1kW ~ 7.5kW 11 and 15 kW, coming soon

The Encoder Resolution Three Scales of Encoder Resolution The 2500 ppr encoder, which is an AB-phase encoder, will send out pulses per revolution. The notation of a 20-bits encoder represents for its level instead of the number of divisions per revolution, because it communicates with servo motor via communication protocol not pulse signal. 17 bits => 160,000 p/r (> 2 17 =131,072) 20 bits => 1,280,000 p/r (> 2 20 =1,048,576)

The Advantage of High Resolution Several Advantages The position of a rotor cannot be known until it is at the division point. The higher resolution, the more positing accuracy. The higher resolution, the better low speed stability. The higher resolution, the smaller acoustical noise.

Evaluate Response Time Domain and Frequency Domain The Settling Time is for time domain where the Bandwidth is for frequency domain. Settling Time ∞ (k / Bandwidth) Speed Gain ∞ (k * Bandwidth)

Easy Way to Think Frequency To Interpret from the View of Fourier Series A period function can be decomposed into a numbers of diversity-frequencies oscillating functions. The sharper the signal, the higher frequency waves are composed. A high bandwidth system can accommodate a command without losing its sharp segment.

The Stiffness To Evaluate the Ability of a System to Resist Disturbance Disturbance exists everywhere. All movements lead to load change can be attributed to disturbance. Higher gain means faster response which can adjust the system to get rid of load change effect fast.

The Rigidity Connected to the Response of a System The more rigid a system, the higher bandwidth it is. The resonance frequency of a rigid system is always higher. It must be taken into account during the developing phase of a machine.

A Stable System Industry V.S. Academic The stability is defined to a system before it turns to self-oscillating in academic. It is unreal for industry even it is not self-oscillating. The stability is asked to fit the requirements of operation of a machine; excellent smooth speed and accurately positioning performance in CNC world, for example.

Abundant Operation Modes The Table Beside is for ASDA-A2 Most of the operation modes are shared by all series. Please reference to user manuals for details.

The Control Skeleton Multiple Cascaded Loops Position loop, Speed loop, and Current loop.

Position Control Loop Position Control Path Position Command Unit, Position Control Unit, Speed Loop, Current Loop, and Vibration Suppression Unit.

Position Command Unit Position Command and Source Selection Pulse Type Selection, Control Mode, Electronic Gear Ratio, Moving Filter, and Position Control Unit.

The Position and Speed (1) The Position Curve Defines Speed The longer the distance moved per unit time, the higher the speed will be.

The Position and Speed (2) Why the S-Curve needed To generate an acceleration zone and a deceleration zone is necessary for a smooth movement.

The Position-Speed-Torque From the View of Real World The Impulse function does not exist in physical world; that is another perspective to see why we need S-Curve. If the acceleration or deceleration zone is short, the system should be with the ability to offer tremendous power in a short time or the drive will operate in saturation and cannot follow the command well.

The Saturation of A Drive What is Saturation A servo driver to output power with maximum ability is called saturation. When saturation occurred, there is impossible to follow the command if the command keeps requesting energy from the servo drive, increasing speed for example. In saturation, the disturbance will have a great impact to the servo system because there doesn’t have any more power for a servo system to cope with external force.

Moving Filter P1-68 The Function of Moving Filter It can smooth command and will come out with certain delay of time.

Low Pass Filter P1-08 Smooth the Position Command The high frequency parts of command will be excluded.

Position Control Unit Tuning the Position Loop Gain Proportional Position Loop Gain, Position Integral Compensation, Position Feed Forward Gain

Important Notice Definition Difference There are two different definitions of “Feed- Forwards” from Delta system to the ones known to public. The “Position Feed-Forward” in Delta is called “Velocity Feed-Forward” for convention, and the “Velocity Feed-Forward” in Delta ASDA system is conventional named “Torque Feed-Forward”.

Proportional Position Loop Gain P2-00 The Rate of Feeding Position Command The higher the proportional position gain, the faster the position command fed into velocity loop. The gain of position loop should be equal or less than ¼ of velocity loop gain to avoid position overshooting.

Overshoot Position Overshoot V.S. Speed Overshoot The position overshoot means the motor crosses over the target position and comes back to the position. The position overshoot sometimes could cause catastrophic disaster. It should always keep in mind during tuning process. The speed overshoot will bring the motor exceed its target speed during transient status. Sometime, the motor will be tuned to 5%~10% speed overshoot to increase system performance.

The Cause of Position Overshoot Loop Gains Do Not Match The closer a loop to the load, the higher loop gain it should be. In Delta system, the speed loop gain had better to set to 4 times over the position loop gain for not producing position overshoot. That’s a general rule, not always but usually.

Position Feed Forward Gain P2-02 Differentiate the Position Command Directly into Speed Command As our notice before, this is called Speed Feed- Forward in convention. The Feed-Forward gain will improve the system response without eroding its absolute stability.

Position Integral Compensation P2-53 Shorten the Position Deviation While Constant Speed This function is only for A2 and B2 series. This function is very easy to induce position overshoot. Check all the machine conditions before you launch it.

Feed Forward V.S. Integrator What Is the Difference The Feed-Forward endeavours to command change where the integrator contains the low frequency disturbance and corrects the steady-state error. The over Feed-Forward gain would not cause a system to self oscillating but integrator does. The Feed-Forward can ease the burden of a control loop.

Speed Control Loop Speed Control Path Speed Command Unit, Speed Control Unit, Current Loop, and Vibration Suppression Unit

Speed Command Unit Speed Command and Source Selection Analog and digital command selection, S-Curve Modifier, Low Pass filter, and Zero Speed Clamp

S-Curve Smooth the Command Acceleration Time, Deceleration Time, and S Time

Zero Clamp P1-38 ZSPD Zero Speed Zero Speed Setting = Speed Mode + Reach the Level Set in P1-38+ ZCLAMP DI Enable Bit 10 in P2-65 can determine if the motor will stop immediately at the moment of all the conditions met. The DI function code of ZCLAMP is 0x05.

Speed Control Unit Tuning the Speed Loop Gain Proportional Speed Loop Gain, Speed Integral Compensation, Speed Feed-Forward Gain, and Anti-Disturbance Gain

Proportional Speed Loop Gain P2-04 Make the System More Responsive The higher the gain, the faster reaction the system. The higher gain stiffens the system which has better ability to handle disturbance. A high gain could induce speed overshoot.

Speed Integral Compensation P2-06 Improve the Steady State Error The steady state error can be corrected by integral gain significantly. The integrator can use to eliminate low frequency disturbance, kinetic friction for example. The integral compensator is very easy to drive the system to unstable status by narrowing down its phase margin.

Speed Feed Forward Gain P2-07 Increase the Command Feeding Speed As our notice before, this is called Torque Feed- Forward in convention. When the command change, feed the difference of command directly into system. That will reduce the burden of the control loop. The transient state could be affected and the speed overshoot may be excited in large gain.

Anti-Disturbance Gain P2-26 The Level of Resisting Disturbance A great tool to contain disturbance. A side effect of extending settling time and reducing its sensitivity. That the default value of P2-26 is equal to P2-06 would be better not to produce speed overshoot.

More About P2-26 Pseudo-Derivative Feedback with Feed-Forward ASDA Series employs a famous control skeleton called PDFF. By adjusting P2-26, the system can be tuned as PI + Feed-Forward or PDF. The PI + Feed-Forward is more responsive where the PDF has better ability to resist disturbance. This is from the view of Speed Loop, and you should integrate the response with the 3 cascaded loops.

Torque Control Loop Torque Control Path Torque Control Unit, and Vibration Suppression Unit

Torque Command Unit Torque Command and Source Selection Analog and digital command selection, and Low Pass filter

What and How of Resonance The Resonance When resonance happens, the system will vibrate because of energy flowing between the motor and the machine. It will bring resonance out if a motor works in a frequency compliant with the frequency of a machine. Inertia loss could lead to resonance that is why the machine requested to be more rigid.

The Resonance from View of Gain Open Loop Gain There is a resonance frequency in a system naturally, and some have more than one resonance frequencies. To lower the operation frequency, low-pass filter, and notch filter can suppress it.

The Excellent Suppression Ability Auto-Notch Filter There are two sets of Auto-Notch and one set of manual Notch in A2 and B2, and only one manual Notch in A, A+, AB, and B.

How the Auto-Notch Works Auto Searching When P2-47 is set to 1 or 2, the system will automatically scan the system resonance frequencies to its registers. The drive will keep the values when P2-47=1,where P2-47=2 is for continuously searching.

The Whole Picture of Notch Filter Auto and Manual Notch Filter (1) : P2-23~P2-24 Manual Mode Notch Filter (2) (3) : P2-43~P2-47 Auto/Manual Mode (Manual / One Time Deal / Continuously Searching)

Notch Filter Attenuation Rate The Attenuation by dB The larger the value, the greater attenuation it is. G(dB) = 20 log 10 (V 1 /V 0 )

Measure Resonance Frequency(1) The PC Scope The channel should be set to “Motor Current: Percentage(%)”. The scope can collect the signals. There are two ways to measure resonance frequency and they are FFT (Fast Fourier Transform) or time interval method.

Measure Resonance Frequency(2) The Fast Fourier Transform Click on the check box of “FFT Display”, press the right mouse button at appropriate place, drag a rectangle, and the frequency spectrum will show.

Measure Resonance Frequency(3) The Time Interval Method Zoon in the trend to a readable size, move mouse to a peak of a wave and right click, move mouse to the consecutive peak, read the time interval, and do the calculation.

Kinetic Friction Compensation What is the Advantage When the motor reverses its direction of rotation, the compensation can reduce the position deviation at the beginning of motor start to move.

How to Evaluate Kinetic Friction (1) Newton’s Laws of Motion An object in a state of uniform motion tends to keep the state of motion until an external force applied to it, the First Law. F = ma, the Second Law. In real world, there is friction. There is a force equal to kinetic friction should be put for maintaining an object in a state of constant speed motion.

How to Evaluate Kinetic Friction (2) Operate the Motor in Constant Speed If an object is in constant speed motion, the force put on it is equal to kinetic friction. Recode the forward and backward motion forces, make a subtraction, and the double scale of the kinetic friction is there.

Measure Kinetic Friction from Scope It Is a Very Convenient Way Make motor move in a constant speed with both directions, and measure the Torque Difference. Set P1-62 = (Torque Difference /2)

Why Torque Difference That Is Consideration for All The Cases If the mechanism is installed vertically, the gravity can be cancelled out of the value of the difference.

Smooth Compensation The Low Pass Filter The Low pass filter can modify the compensation for kinetic friction force.

Under and Over Compensation Compensate the Right Force While Under, increase P1-62 of its level or lower P1-63 low-pass filter While Over, decrease P1-62 of its level or higher P1-63 low-pass filter.

First Step to Tune A System P1-37 J-L Ratio The Inertia Ratio will decide how the energy flowing into the system. It is the first and very important step to let system get the right ratio. You can use the ASDA-Soft to help.

To Evaluate Inertia from Scope An Alternative Way If the machine cannot operate over 200 rpm, there could be a trouble to evaluate J-L ratio (P1-37) from ASDA servo drive. The PC Scope can help it out.

To Tune the Bandwidth Auto Calculation of ASDA-soft Set the bandwidth small at first, increase it until noise comes out from the motor, and then reduce the bandwidth until the sound gone. The tuned bandwidth could be the highest possible bandwidth for this system.

Suppress the Resonance Auto and Manual If ASDA-A2 or ASDA-B2 is tuning, the Auto-Notch can use to deal with resonance. If an old series of ASDA drive is tuning, the “time interval method” of scope should be selected.

Large Value Scope 32 Bits Scope Supported and No More Saw-Tooth ASDA-Soft supports 32 bits scope in ASDA-A2 and ASDA-B2. This a very convenient tool for debugging.

What is PUU Pulse of User Unit The PUU is a unit which is scaled by the electronic gear. This will bring out an advantage, and that is “YOU SEE WHAT YOU COMMAND”. For example, if you send PUU for command and you can read from the feedback PUU by ignoring the E-Gear Ratio.

Tuning the Performance A Popular Channel’s Combination There are debugging skills based on experience, but the combination of Speed Command, Motor Speed, Motor Current, and Position Error is a very popular one.

Thank You