Renishaw SPA1 User manual

SPA1 servo tuning guide
Installation guide
H-1000-5227-06-B

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service marks, trademarks, or registered trademarks of their respective owners.
Renishaw part no: H-1000-5227-06-B
Issued: 12 2006

SPA1 servo power amplifier
tuning guide

2Care of equipment
Care of equipment
Renishaw probes and associated systems are precision tools used for obtaining precise measurements
and must therefore be treated with care.
Changes to Renishaw products
Renishaw reserves the right to improve, change or modify its hardware or software without incurring any
obligations to make changes to Renishaw equipment previously sold.
Warranty
Renishaw plc warrants its equipment for a limited period (as set out in our Standard Terms and Conditions
of Sale) provided that it is installed exactly as defined in associated Renishaw documentation.
Prior consent must be obtained from Renishaw if non-Renishaw equipment (e.g. interfaces and/or cabling)
is to be used or substituted. Failure to comply with this will invalidate the Renishaw warranty.
Claims under warranty must be made from authorised service centres only, which may be advised by the
supplier or distributor.
Trademarks
Windows 98, Windows XP, Windows 2000 and Windows NT are registered tradenames of the Microsoft
Corporation.
All trademarks and tradenames are acknowledged.
References and associated documents
It is recommended that the following documentation is referenced to when installing the UCC.
Renishaw documents
Documentation supplied on Renishaw UCC software CD.
Document number Title
H-1000-5057 UCC controller programmer’s guide
H-1000-5058 UCC Renicis user’s guide
H-1000-5223 UCC2installation guide
H-1000-5068 SPA1 installation guide

Contents 3
Contents
1Introduction..........................................................................................................................................5
2SPA1 commissioning sequence ..........................................................................................................6
2.1 Initial machine ini file creation ..............................................................................................6
2.1.1 Common parameters ............................................................................................6
2.1.2 Machine and move configuration..........................................................................8
2.2 Renicis sequence.................................................................................................................9
2.2.1 Initial steps............................................................................................................9
2.2.2 Close position loop .............................................................................................10
2.2.3 Set offset PA controls .........................................................................................11
2.2.4 Calc servo gain ...................................................................................................12
2.2.5 Velocity loop tuning.............................................................................................13
2.2.6 Adjustment of proportional and integral gains ....................................................14
2.3 Renicis position loop tuning ...............................................................................................15
2.3.1 Setting the uncompensated gain ........................................................................15
2.3.2 Applying acceleration feedback ..........................................................................17
2.4 Servo tuning test ................................................................................................................19
2.4.1 Servo tuning objectives.......................................................................................21
2.4.2 Applying velocity feed-forward............................................................................22
2.4.3 Scanning tuning procedure.................................................................................23
3Rotary table tuning procedure ...........................................................................................................24
3.1 Overview ............................................................................................................................24
3.1.1 Initial settings ......................................................................................................24
3.2 Tuning ................................................................................................................................25
3.2.1 Velocity loop tuning.............................................................................................25
3.2.2 Position loop tuning ............................................................................................26
4Definitions..........................................................................................................................................27
4.1 Uncompensated gain .........................................................................................................27
4.2 Acceleration feedback........................................................................................................27
4.3 Dynamic integrator .............................................................................................................27
4.4 Velocity feed-forward .........................................................................................................27
4.5 I2t Time ...............................................................................................................................28
4.6 IET Time.............................................................................................................................28
4.7 Overshoot (per axis)...........................................................................................................28
4.8 Following error (per axis, already existing) ........................................................................28
4.9 Steady state error (per axis)...............................................................................................28
4.10 Settling time (per axis) .......................................................................................................28
4.11 Tunnelling error (for the 3D move) .....................................................................................28

4Contents
5Glossary of terms.............................................................................................................................. 29
6Revision history ................................................................................................................................ 30
6.1 What’s new in release 01-A............................................................................................... 30
6.2 What’s new in release 02-A............................................................................................... 30
6.3 What’s new in release 03-A............................................................................................... 30
6.4 What’s new in release 04-A............................................................................................... 30
6.5 What’s new in release 05-A............................................................................................... 30
6.6 What’s new in release 05-B............................................................................................... 30
6.7 What’s new in release 06-A............................................................................................... 30
6.8 What’s new in release 06-B............................................................................................... 30

Introduction 5
1 Introduction
The object of this UCC servo tuning user’s guide is to provide a user-friendly publication to assist in the
task of setting up the servo response of the CMM. When used in conjunction with our “RENICIS”
installation / fault finding software, this document should enable a competent technician to set up a CMM
either at the assembly plant or on-site.
The UCC controllers have a powerful range of control elements to assist with tuning (attaining the required
performance) the CMM system, including; gain control, lead and lag filters, dynamic integrator,
acceleration feedback and velocity feed-forward.
The theories behind optimal tuning of control system are lengthy and complex, so we have tried in this
issue to automate the set-up steps that deal with servo-optimisation. A set of performance indices are
made available to enable checking of the machine tuning at all times. A report that records all these can
be generated.

6 SPA1 commissioning sequence
2 SPA1 commissioning sequence
The following section outlines the recommended procedure to commission the SPA1 or analogue based
3rd party servo power amplifiers.
This procedure assumes that the system being installed is a new installation and little information is known
about the machine’s servo system characteristics.
2.1 Initial machine ini file creation
Using Renicis create a new machine ini file, the following critical parameters must be correctly specified
for the initial installation process.
NOTE: Most of the default parameters specified in the machine configuration file can remain as default.
2.1.1 Common parameters
MachineDescription section
Make This should be the make of machine
Model This should be the model of the machine
Miscellaneous section
LogFilePath This should be a valid file path
MachineConfiguration section
ProbeHeadType Probe head type fitted to the machine
XscaleIncrement Resolution of the X axis scale in mm
YscaleIncrement Resolution of the Y axis scale in mm
ZscaleIncrement Resolution of the Z axis scale in mm
Xtravel Distance of machine X axis travel in mm
Ytravel Distance of machine Y axis travel in mm
Ztravel Distance of machine Z axis travel in mm
MoveConfiguration section
* MaximumMoveSpeed Maximum move speed of the CMM in mm/s
MaximumMoveAcceleration Maximum move acceleration of the CMM in
mm/s/s
* See section 0 for an explanation of this parameter and its importance.
TORQUEMODE (if used)
ControlMode Torque mode is enabled or not

SPA1 commissioning sequence 7
MachineIOLogic
AmpifierOK Logic level active high or low
CMMdeclutch Logic level active high or low
ESTOPtripped Logic level active high or low
AirPressureLow Logic level active high or low
ZaxisCrash Logic level active high or low
MotorsEngaged Logic level active high or low
OuterLimitXPositive Logic level active high or low
OuterLimitXNegative Logic level active high or low
OuterLimitYPositive Logic level active high or low
OuterLimitYNegative Logic level active high or low
OuterLimitZPositive Logic level active high or low
OuterLimitZNegative Logic level active high or low
InnerLimitXPositive Logic level active high or low
InnerLimitXNegative Logic level active high or low
InnerLimitYPositive Logic level active high or low
InnerLimitYNegative Logic level active high or low
InnerLimitZPositive Logic level active high or low
InnerLimitZNegative Logic level active high or low
OuterLimitY2Positive Logic level active high or low
OuterLimitY2Negative Logic level active high or low
InnerLimitY2Positive Logic level active high or low
InnerLimitY2Negative Logic level active high or low
DUALY section (if fitted)
DualAxisScaleIncrement Resolution of the dual axis scale in mm
WhichAxisDual Which axis is the dual axis
DualDriveEnable Is the dual drive switched on
ScaleInputLocation UCC input location address
DriveOutputLocation UCC output location address
RotaryTable (if fitted)
MeasurementUnits Units of increment for the rotary table
WscaleIncrement Resolution of the W axis scale
WmaximumMoveSpeed Maximum move speed of the rotary table
WmaximumMoveAcceleration Maximum move acceleration of the rotary table
SPAX
ChannelNumber = 0
SPAType = SPA1
SPAY
ChannelNumber = 1
SPAType = SPA1
SPAZ
ChannelNumber = 2
SPAType = SPA1

8 SPA1 commissioning sequence
2.1.2 Machine and move configuration
This is a very important part of the machine set-up where all the physical and motion properties are
defined.
CAUTION: Particular care is needed in specifying the maximum move speed and acceleration
since this defines the velocity gain of the remainder of the CMM servo system (the motors, the
tacho-generators (if fitted) and the drive gearing).
The “MaximumMoveSpeed” is a theoretical speed which corresponds to a maximum demand being
applied to the servo power amplifier. To control a specified speed, we apply a margin about that speed to
effect control. This is set to 20%. This means that the actual maximum move speed is 80% of the
“MaximumMoveSpeed” specified in the machine configuration file i.e. if you set “MaximumMoveSpeed” to
500 mm/s the maximum move speed you can request is 400 mm/s.
If maximum move speed is altered after the CMM has been commissioned (with no change in the CMM
hardware), two problems will become apparent: -
Problem 1
All machine speeds can be altered. e.g. if the maximum move speed value is halved, this implies that the
full 10 V motor command will now produce only half the previous speed. The controller will therefore
compensate by sending speed commands to the motors, which are twice the original values to get the
same target machine speeds. This will result in much faster moves than intended, with probably “over-
speed” and “overdriven” faults being produced.
NOTE: The machine speed in a command (move or scan) is limited to only 80% of the maximum move
speed to ensure servo control at all times.
Problem 2
If the machine’s performance characteristics change then some of the settings will become invalid. The
machine will need to be re-tuned.
!

SPA1 commissioning sequence 9
2.2 Renicis sequence
2.2.1 Initial steps
1. Start the commissioning process by ensuring the step icon on the toolbar is not indented and then
click on the GO icon on the toolbar, as shown in the figure 1 below:
Figure 1
2. The Renicis commissioning step list will now be displayed within a window that will open on the
desktop, as shown in the figure 2 below:
Figure 2
3. Highlight the Welcome step within the list and then click on the GoToStep button to start the
commissioning process.
4. Proceed through the following Renicis steps following the instructions:
•Welcome
•Connector and interface details
•Check CMM
•Test link
•Emergency stop
•Other safety matters
•Check read heads

10 SPA1 commissioning sequence
5. If problems are experienced with any of the above steps, refer to the Renicis user guide (Renishaw
part number H-1000-5058) or the appropriate UCC1, UCClite or UCC2installation guide.
2.2.2 Close position loop
For the following tests the CMM motors will frequently be engaged by Renicis in either open or closed loop
modes. To reduce the risk of damage or injury the user is advised to disable the motors (and amplifiers)
on axes which are not active in any given test until such time as all axes are set up and operating
correctly.
WARNING: At this stage, the user should be aware that the CMM motors are being engaged for
the first time and that incorrect wiring or other drive faults may cause unpredictable machine
behaviour. The user must have unobstructed access to the emergency stop switch, and all other
personnel must be kept away from the working region of the CMM.
A prompt screen will be displayed for user input to confirm that it is possible for Renicis to engage all the
drives for a very brief period (0.5 s) to assess the stability of the servo loops.
If the operator confirms that there were no unexpected moves after the initial servo stability test, the
operator will be prompted to engage the drives for a small movement (5 mm), again to test for servo
instability.
If the operator confirms the machine to be stable in both these tests, Renicis will assume that it is safe to
move the CMM with the position loop closed during the subsequent Renicis tuning stages.
NOTE: Each time Renicis is restarted it has to ask the operator whether the CMM is safe to use in closed-
loop moves and if the answer is “no” the operator will be warned before engaging the drives
!

SPA1 commissioning sequence 11
2.2.3 Set offset PA controls
The purpose of this step is to permit any servo offset apparent on the UCC controllers to be matched with
the servo power amplifier fitted to the system.
The following system preparations are advised prior to the operator progressing through the steps of the
Renicis commissioning process:
• Move the quill of the machine to approximately the centre of its working volume, to permit freedom of
movement during this tuning step.
• The power amplifier gain (sometimes called the ‘P’ or ‘Proportional gain’ term) should be set at a very
low level to give a low speed of movement.
• Any Integral (I) or Derivative (D) terms used on the power amplifier should be turned to zero or at least to
their minimum settings and set any offset adjustment to the middle of its travel.
Following the operator prompt, Renicis will engage the drives for the X, Y (1 & 2), Z and W axes (as
appropriate) with a velocity demand of zero. The operator can now adjust the servo power amplifier's
offset control to minimise any machine movement (drift) for all axes.
NOTE: The rotary table (W axis) will only be displayed if it is enabled. The Y2 axis will also only be
displayed if it is enabled.
Figure 3
The detected machine velocity is shown in the screen (see above) as a bar graph for each axis.
The arrow shown in the 'Z-axis' bar example indicates that the velocity is increasing in the negative
direction. When a value is beyond the displayable maximum, but decreasing, the arrow will be displayed
pointing toward the null (centre of display) position.
By 'right-clicking' on the display, it is possible to modify the default settings for the display these include
the maximum (+ve and -ve) displayed value and the threshold value at which the bar colour will change
from green (an 'acceptable value') to red.

12 SPA1 commissioning sequence
2.2.4 Calc servo gain
The purpose of this step is to set the velocity gain of the system to the theoretical value
(MaximumMoveSpeed / 10)
The velocity gain which Renicis will use as a target is calculated from the Maximum Move Speed as
specified in the Machine ini file, such that this speed will correspond to the maximum value of motor
command signal from the controller, i.e. 10 volts. For example, if the machine is to be capable of a
maximum speed of 400mm/second, the gain required is 40 mm/sec per volt.
NOTE: In normal use programmed moves will be limited to 80% of this maximum by the controller (320
mm/sec in the above example) so that the servo system commands do not saturate during high
accelerations.
This commissioning step will move the machine in one axis at a time, starting with the X axis. Initially
Renicis will move the machine slowly at nominally 5 mm/sec so that the user can confirm that it is safe to
proceed to the full test speed of 25 mm/sec.
The actual speed (red line) will be displayed on a continuously updating graph that will also show the
demand speed (blue line), see figure 4 below. The user then can adjust the servo power amplifier
"MaxSpeed" potentiometer until these coincide as closely as possible.
Figure 4
The machine moves alternately in positive and negative directions over a small part of its travel while the
user makes these adjustments. Few machines are completely symmetrical in this respect, so that some
compromise may be required in the settings.
When the installer is satisfied with the settings of the amplifier gain, activating the ‘Next Step’ button within
Renicis the program will drive the machine back to the starting position and carry out one full movement
cycle. This will calculate the final value of the velocity gain (Kv) which is then used to update the value
stored in the machine ini file.
This process is then repeated for the other axes.
During these tests, the servo position loops are open so there is a possibility that some drift may occur in
all axes. It is recommended that the tests are carried out sequentially to avoid the machine drifting too far
from its starting point. When each step of the test is started, the machine will be repositioned at the
original central position.

SPA1 commissioning sequence 13
2.2.5 Velocity loop tuning
This test moves the CMM forwards and backwards by the distance entered. This movement will normally
be shown complete on the graph against time. Selecting 'fwd + rev. move superimposed' will invert the
reverse trace and display it against the forward trace so that an easier comparison may be made.
1. It is recommended that initially the tests are completed on individual axis, the X axis is selected by
deselecting the Y and Z axis check boxes.
2. Run the test, to start with by clicking the Go button. Check the operate continuously box to keep the
machine moving, otherwise the machine will stop after one cycle.
NOTE: If the machine is unstable, it is recommended that the proportional gain pot is reduced until you
have stability and can continue with the tests.
Increasing the acceleration value for this test will give a sharper square wave stimulus to the machine.
The test will not change the maximum acceleration value stored in the UCC Configuration File.
Figure 5
If the machine response amplitude does not match the demand you could get the following message:
Figure 6
Check the machine is still in the centre of its operating range, move it if necessary, click on the OK button,
click on the reset data button, then adjust the gain setting and continue the test by clicking on GO.

14 SPA1 commissioning sequence
2.2.6 Adjustment of proportional and integral gains
Initially the response displayed may look as shown in figure 7 below:
Figure 7
The objective is to get the machine response (blue line) as close to the demand (red line) but with no or
minimal overshoot. The optimum performance will require some adjustment of the gains and these should
be varied to confirm that no further improvements can be obtained.
When complete the response should look something like:
Figure 8
When the system has been tuned it is recommended that the machine speed for the velocity loop test is
reduced to match the default trigger / scanning speed and the test is repeated to ensure that the system
response is still tuned.
NOTE: If it is necessary to change the tuning settings for the trigger / scanning speed then these values
are recommended to be used for the installation.

SPA1 commissioning sequence 15
2.3 Renicis position loop tuning
NOTE: To keep the machine response “balanced”, the same tuning parameter values must be used for all
axes, with the exception of acceleration feedback.
2.3.1 Setting the uncompensated gain
In this section we will be increasing the uncompensated gain KPto a safe maximum before switching on
any conditioning filters. To do this, it is necessary to run a three axis move.
1. Ensure button is not depressed and operate the button on the RENICIS toolbar. Highlight
the “Uncompensated Gain Test” step, run the “Uncompensated Gain Test” by clicking the “Go to Step”
button.
2. Follow the instructions given until the test dialog is displayed, refer to figure 9. Ensure that the default
value of 0.2 is indicated, then click on the "Go" button. The machine should move in a forward and
reverse cycle in all three axes and the following error present during the move displayed on the
graphs. Examine the graphs produced (refer to figure 10).
Figure 9
3. If the machine runs smoothly and no periodic oscillations are apparent (refer to figure 10). The
uncompensated gain can be increased (either directly in the edit box, or by clicking on the upper 'spin'
button to the right of the edit box) by approximately 10%, now referred to as KP1, and the test repeated
by clicking on the "Go" button again.
Continue increasing the value of KP1 until one of the axes reaches the brink of instability (refer to
figure 11), then reduce the value by approximately 20% to give a stability margin and re-check for
stability. If the system is stable and no oscillations are apparent then this value is called the
“Uncompensated Proportional Gain” KP2 (and is set automatically to be the same for all axes).
NOTE: On some systems, and with very low gains, it is possible that timeouts will occur during the move.
Should this occur, increase the position tolerance by changing the value in the edit box provided. The new
value will take effect at the beginning of the next move, i.e. it will not make any effect whilst the system is
moving.

16 SPA1 commissioning sequence
Figure 10
Figure 11
If any axes become unstable (Y axis in figure 11), reduce KP1 by 20% and check again, see step 2.
NOTE: All axes must have the same KP1. The value of KP2 must be such that ALL axes display stability.

SPA1 commissioning sequence 17
2.3.2 Applying acceleration feedback
Acceleration feedback is another level of control that selectively increases the apparent inertia of the
machine, allowing us to increase the gain still further before the machine becomes unstable. Machines
react in different ways to acceleration feedback so the amount of gain increase can vary between zero and
ten times.
NOTE: Experience has shown that the use of acceleration feedback is usually not required and therefore
not recommended for machines that have an uncompensated gain of ≥0.2.
1. The first stage is to increase the proportional uncompensated gain value so that the machine is just
unstable using the uncompensated gain step, refer to 2.3.1, record which axes are unstable.
2. It is now necessary to activate the acceleration feedback term (KA) in the axes that are unstable.
•Enter the machine configuration screen
•Select the "ServoConfiguration" tab and scroll down to locate the edit boxes for the
acceleration feedback terms KA(X), KA(Y) and KA(Z).
•Set the initial acceleration feedback value (KA) for the axis that has shown signs of instability
to 0.00005. Repeat for each unstable axis (Note: For any stable axes the acceleration
feedback value remains set to zero).
•Check for stability by running the “Uncompensated Gain Test refer to 2.3.1
3. If the machine is stable, increasing the uncompensated gain by a further 10 – 20%. If the machine
is displaying instability as for the Y axis in figure 21, increase the value of KA(refer to step 2) in the
unstable axes by a further 0.00005 (to do this follow step 2) and repeat the uncompensated gain
test.
•If the acceleration feedback value is too high the machine will produce an audible singing and
must be reduced by 10 to 20 % in the unstable axes. Run the “Uncompensated Gain Test
refer to 2.3.1 to ensure the machine is stable. If it is not stable repeat this step.
4. Repeat these steps, raising the values of KAand KP1 until final values of KAand KPare found (see
figure 22). The final value of KPobtained during this process is referred to as KP3.
This will be the new “Uncompensated Gain”.
NOTE: It is necessary to increase the amount of acceleration feedback slowly in iterative steps as shown
in figure 12, so that the maximum value of KPcan be found. This is in the peak between gain induced
instability line and acceleration induced instability line. The consequence of increasing the acceleration
feedback in one large step without increasing the proportional gain on intermediate steps is illustrated in
figure 13, note the final value of KPis far lower than in that obtained in figure 12.
Once the values for acceleration feedback are determined they must be left unchanged. Their values may
be different, but the value of KP3 must be the same for each axis.

18 SPA1 commissioning sequence
Figure 12
Figure 13
NOTE: At this point, if the positioning is good enough (within specifications), then no further tuning will be
necessary.