Renishaw RCU10 User manual

Installation and user’s guide
M-9904-1122-09-A
RCU10 quadrature compensation unit

Document information
Document number: M-9904-1122-09-A
Issue date: 03 2019
© 2004-2019 Renishaw plc. All rights reserved.
Care of equipment
The Renishaw RCU10 compensation system and
associated products are precision instrumentation
products and components and must therefore be
treated with care.
Changes to Renishaw products
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change or modify its products and documentation
without incurring any obligation to make changes
to Renishaw equipment previously sold or
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Safety
This manual gives recommendations for the
safe installation and configuration of the RCU10
compensator system, and associated ancillary
products.
It is the sole responsibility of the OEM/retrofit
company to ensure that, in safety critical
applications, any failure or deviation from
expected operation of this product, howsoever
caused, shall not cause the machine to become
unsafe.
It is the machine supplier’s responsibility to
ensure that the user is made aware of any
hazards that may be involved in the operation
of their machine, including those covered in
Renishaw product documentation, and to ensure
that adequate guards and safety interlocks are
provided.
This manual suggests a number of safety
measures that can be included in machine
design. However, it is the sole responsibilty of the
OEM/system integrator to specify and integrate
measures suitable for the application.
Symbol definition
The following symbol is used in this manual and
in the software to indicate areas requiring special
attention:
WARNING: Information that is vital for
the safe installation and operation of the
RCU10 system.
Warranty
Renishaw plc warrants its equipment provided
that it is installed and operated exactly as defined
in associated Renishaw documentation.
Claims under warranty must be made from
authorised service centres only, which may be
advised by the supplier or distributor.
FCC
This device complies with part 15 of the FCC
Rules. Operation is subject to the following two
conditions: (1) This device may not cause harmful
interference and (2) this device must accept any
interference received, including interference that
may cause undesired operation.
This equipment has been tested and found
to comply with the limits for a Class A digital
device, pursuant to Part 15 of the FCC Rules.
These limits are designed to provide reasonable
protection against harmful interference when
the equipment is operated in a commercial
environment. This equipment generates, uses,
and can radiate radio frequency energy and,
if not installed and used in acordance with
the instruction manual, may cause harmful
interference to radio communications. Operation
of this equipment in a residential area is likely to
cause harmful interference in which case the user
will be required to correct the interference at his
own expense.
The user is cautioned that any changes or
modifications not expressly approved by
Renishaw plc or authorized representative could
void the user’s authority to operate the equipment.
EC compliance
Renishaw plc declares that the RCU10
compensator system and transmitters comply
with the applicable directives, standards and
regulations. A copy of the full EC Declaration of
Conformity is available at the following address:
www.renishaw.com/RLECE
!

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The use of this symbol on Renishaw products
and/or accompanying documentation indicates
that the product should not be mixed with
general household waste upon disposal. It is the
responsibility of the end user to dispose of this
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and prevent potential negative effects on the
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contact your local waste disposal service or
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The use of this symbol on the batteries,
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or protected from short circuiting prior to disposal.
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Material 94/62/EC
code
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Outer box Cardboard -
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Information required by Article 33(1) of
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RoHS compliance
Compliant with EC directive 2011/65/EU (RoHS).

General safety notice i
General safety notice
The Renishaw laser encoder and compensator systems are designed for integration into
the primary position feedback loop of a motion system. It is essential that the system is
installed in accordance with the instructions in the installation guide and it is the
responsibility of the system integrator to ensure that, in the event of a failure of any part of
the Renishaw system, the motion system remains safe.
In the case of motion systems with powers or speeds capable of causing injury, it is
essential that appropriate safety protection measures are included in the machine design.
Further guidance on this can be found in the European Standard EN292 “Safety of
machinery – Basic concepts, general principles for design”. It is the sole responsibility of
the OEM/system integrator to select the safety measures appropriate for their application.
The following is a list of measures that should be considered as part of that process.
1. The Renishaw system includes an Error signal output. The control system must be
designed to stop the axis motion if this error output is asserted. In addition to the
Error signal, the position feedback signals can also be configured to go tristate
(open circuit) under fault conditions. Some controllers can be programmed to detect
this, thereby providing a further level of protection in case of failure of the error
signal output (see item 3 below). If the controller is not capable of detecting open
circuit position feedback signals, this option must not be enabled.
2. The axis must include physical limit switches which, when tripped, will stop axis
motion before damage occurs (soft limits alone are insufficient). Note that in the
case of thermally compensated systems, positional corrections of several hundred
ppm are possible. This should be taken into account when defining the relative
positions of soft and hard axis limits.
3. Cable breakage detection (encoder disconnect). The position feedback and Error
signal lines are all provided as differential line driven pairs. Failure in the cable or
failure of the line drivers can be detected by checking that these differential pairs are
always being driven in opposing states. If the lines are not in opposing states, the
motion must be stopped.
4. Motor torque monitoring. If the motor torque exceeds an expected limit, the axis of
motion must be stopped.
5. The machine must include an emergency stop button.
6. Following error detection, if the difference between the controller demand position
and the axis feedback position exceeds an expected limit, then the axis motion must
be stopped.
7. Guards, viewing windows, covers and interlocks may be used to prevent user
access to hazardous areas, and to contain ejected parts or materials.
8. If the machine includes an independent tacho (velocity) feedback system, this
should be cross-checked with the position feedback. For example, if the tacho
indicates the axis is moving, but the position feedback doesn’t, then the axis motion
must be stopped.

ii General safety notice
9. In the case of synchronised parallel motion systems (for example twin rail gantry
drive systems), the relative positions of master and slave axes should be monitored.
If the difference in their positions exceeds an expected limit, then axis motion must
be stopped.
Note: In the case of measures 6 – 9, the limits need to be selected carefully depending on
the application and the type of position compensation selected to avoid false alarms.
For further advice consult the appropriate machinery safety standards.

Contents iii
Contents
Section 1 System overview
1.1 Introduction............................................................................................................ 1-2
1.2 System overview ................................................................................................... 1-2
1.3 Compensation functions........................................................................................ 1-4
1.3.1 Scale factor ............................................................................................... 1-4
1.3.2 Air refractive index compensation............................................................. 1-4
1.3.3 Encoder thermal expansion compensation...............................................1-5
1.3.4 Workpiece thermal expansion compensation ........................................... 1-5
1.3.5 Structure thermal compensation............................................................... 1-7
1.4 Operational functions............................................................................................. 1-8
1.4.1 Selectable parameter tables ..................................................................... 1-8
1.4.2 Compensation buffering............................................................................ 1-8
1.5 System components.............................................................................................. 1-9
1.6 Installation procedure overview...........................................................................1-11
Section 2 System design
2.1 Requirements ........................................................................................................ 2-2
2.2 Sensors and sensor networks............................................................................... 2-3
2.2.1 Environment sensors................................................................................. 2-3
2.2.2 Sensor network connection....................................................................... 2-4
2.3 Electrical connections............................................................................................ 2-5
2.3.1 Connector positions................................................................................... 2-5
2.3.2 Connector functions .................................................................................. 2-6
J1 – 24 V dc power.................................................................................... 2-6
J2 – Controller output................................................................................ 2-6
J3 – Encoder input .................................................................................... 2-6
J4 – Reference switch port........................................................................ 2-7
J7 – Auxiliary I/O....................................................................................... 2-8
J8 – PC port .............................................................................................. 2-9
2.4 Velocity/resolution/bandwidth considerations........................................................ 2-9
2.4.1 Encoder input frequency .........................................................................2-10
2.4.2 Output frequency.....................................................................................2-10
2.5 Referencing .........................................................................................................2-12
2.5.1 Signal format and re-synchronisation......................................................2-12
2.5.2 Referencing options ................................................................................2-14
2.6 RCU10 component mounting..............................................................................2-17
2.6.1 RCU10-XX-XX or RCU10-PX-XX ...........................................................2-17
2.6.2 Air temperature sensor............................................................................2-18
2.6.3 Material temperature sensor ...................................................................2-19
2.6.4 Sensor distribution box............................................................................2-20
Section 3 Kit configuration and part identification
3.1 Defining kit numbers.............................................................................................. 3-2
3.2 Kit numbers and part identification........................................................................ 3-3
3.2.1 RCU10 kit numbers (laser encoder based systems) ................................3-3
3.2.2 RCU10 kit numbers (non-laser encoder based systems)......................... 3-4
3.3 Additional components and part identification....................................................... 3-5

iv Contents
Section 4 System installation
4.1 System installation.................................................................................................4-2
4.1.1 Hardware installation and initial power-up ................................................4-2
4.1.2 RCU10 address set-up..............................................................................4-2
4.1.3 Electrical installation..................................................................................4-4
4.1.4 RCU CS settings .......................................................................................4-4
4.2 System configuration.............................................................................................4-5
4.2.1 System configuration.................................................................................4-6
4.2.2 Sensor network configuration....................................................................4-7
4.2.3 Compensation settings configuration........................................................4-8
4.2.4 Parameter settings configuration.............................................................4-13
4.2.5 Transmitting the configuration.................................................................4-15
4.3 Configuration validation .......................................................................................4-16
Section 5 Controller integration
5.1 Introduction............................................................................................................5-2
5.2 Safety function testing ...........................................................................................5-2
5.2.1 Encoder error testing.................................................................................5-2
5.2.2 RCU10 error testing...................................................................................5-3
5.2.3 Testing environment sensors....................................................................5-5
5.2.4 Auxiliary I/O connector input functions......................................................5-6
5.2.5 Reference mark connector function ..........................................................5-8
5.2.6 Encoder considerations.............................................................................5-9
5.2.7 Integration procedure ..............................................................................5-10
5.2.8 Making corrections ..................................................................................5-10
5.2.9 Closing the control loop...........................................................................5-11
5.2.10 Motor drive tuning....................................................................................5-11
5.2.11 Referencing the system...........................................................................5-12
Section 6 Operation
6.1 Standard operation................................................................................................6-2
6.2 RCU CS status during operation ...........................................................................6-2
6.2.1 Compensation display...............................................................................6-3
6.2.2 Sensor display...........................................................................................6-4
6.2.3 Diagnostics display....................................................................................6-5
6.3 General maintenance ............................................................................................6-6
Appendix A RCU10 system specifications
A.1 RCU10 system performance .................................................................................A-2
A.2 Component performance.......................................................................................A-4
A.2.1 Compensation unit.....................................................................................A-4
A.2.2 Air sensor ..................................................................................................A-5
A.2.3 Material sensor..........................................................................................A-5
A.2.4 Pressure sensor ........................................................................................A-5

Contents v
Appendix B Connector pinout and hardware installation details
B.1 Introduction........................................................................................................... B-2
B.2 24 V dc power (J1) ................................................................................................B-2
B.2.1 Connector pinout.......................................................................................B-2
B.2.2 Wiring requirements..................................................................................B-3
B.3 Controller output (J2).............................................................................................B-4
B.3.1 Digital feedback signals ............................................................................B-4
B.3.1.1 Connector pinout.......................................................................B-4
B.3.1.2 Wiring requirements..................................................................B-5
B.3.2 Analogue feedback signals .......................................................................B-6
B.3.2.1 Connector pinout.......................................................................B-6
B.3.2.2 Wiring requirements..................................................................B-7
B.4 Encoder input (J3) .................................................................................................B-8
B.4.1 Connector pinout.......................................................................................B-8
B.4.2 Wiring requirements..................................................................................B-9
B.5 Reference switch port (J4)...................................................................................B-10
B.5.1 Connector pinout.....................................................................................B-10
B.5.2 Wiring requirements................................................................................B-10
B.6 Auxiliary I/O (J7)..................................................................................................B-11
B.6.1 Connector pinout.....................................................................................B-11
B.6.2 Wiring requirements................................................................................B-11
B.7 PC port (J8) .........................................................................................................B-13
B.7.1 Connector pinout.....................................................................................B-13
B.7.2 Wiring requirements................................................................................B-13
B.8 Fastlink port.........................................................................................................B-14
B.9 Sensors (J5, J6) ..................................................................................................B-14
B.9.1 Connector pinout.....................................................................................B-14
B.9.2 Wiring requirements................................................................................B-15
Appendix C RCU CS
C.1 RCU CS.................................................................................................................C-2
C.1.1 Overview ...................................................................................................C-2
C.1.2 Access levels.............................................................................................C-2
C.1.3 Operating modes.......................................................................................C-3
C.1.4 Configuration data.....................................................................................C-4
C.2 RCU CS installation...............................................................................................C-5
C.2.1 System requirements ................................................................................C-5
C.2.2 Installation procedure................................................................................C-6
C.2.3 Screen layout ............................................................................................C-7
Appendix D Compensation system status information and diagnostics
D.1 Diagnostics............................................................................................................D-2
D.1.1 Process overview......................................................................................D-2
D.2 Error descriptions ..................................................................................................D-3
D.3 RCU CS information screens ................................................................................D-4
D.3.1 Compensation system screen...................................................................D-4
D.3.2 Compensation axis screen........................................................................D-8
D.3.3 Sensor data screen...................................................................................D-9
D.3.3.1 Individual “View status” screen ...............................................D-10

vi Contents
D.3.4 Diagnostics............................................................................................. D-13
D.3.4.1 System status screen..............................................................D-13
D.3.4.2 RCU diagnostics screen (top display).....................................D-14
D.3.4.3 RCU diagnostics – Configuration tab......................................D-15
D.3.4.4 Axis diagnostics – Compensation tab .....................................D-17
D.3.4.5 Axis diagnostics – Communication tab....................................D-19
D.3.4.6 Axis diagnostics – Sensors tab ...............................................D-21
Appendix E Commissioning tests
E.1 System performance testing..................................................................................E-2
E.1.1 Prerequisites..............................................................................................E-2
E.1.2 Test 1 – Linear compensation (air refractive index or encoder scale
compensation)...........................................................................................E-3
E.1.3 Test 2 – Workpiece thermal expansion compensation .............................E-4
E.1.4 Test 3 – Workpiece thermal expansion at higher temperatures ...............E-5
E.1.5 Test 4 – Workpiece temperature change at material reference position ..E-5
E.1.6 Test 5 – Static workpiece temperature change at distance ......................E-6
Appendix F Extended capability
F.1 Extended RCU10 system capability......................................................................F-2
F.1.1 Extended system capability.......................................................................F-2
F.1.2 Extended system status monitoring ..........................................................F-2
F.1.2.1 Extended status monitoring.......................................................F-2
F.1.3 Axis referencing with extended error lines ................................................F-4
F.1.4 Controlling workpiece compensation from motion control system output
lines ...........................................................................................................F-5
F.1.4.1 Introduction................................................................................F-5
F.1.4.2 Enabling workpiece compensation............................................F-5
F.1.4.3 Disabling workpiece compensation...........................................F-5
F.1.4.4 Suspending workpiece compensation.......................................F-6
F.1.4.5 Multiple fixturing with workpiece compensation ........................F-6
F.1.5 Parameter table selection..........................................................................F-7
F.1.6 Compensation buffering ............................................................................F-8
F.1.7 Configuration of advanced features ..........................................................F-8
F.1.7.1 Multiple parameter tables..........................................................F-8
F.1.7.2 Operating with multiple parameter tables..................................F-9
F.2 RCU CS – Additional functionality.......................................................................F-12
F.2.1 Additional RCU CS configuration functionality........................................F-12
F.2.1.1 Saving the configuration..........................................................F-12
F.2.1.2 Loading a configuration...........................................................F-13
F.2.1.3 Setting the PC communication port.........................................F-14
F.2.1.4 Configuring passwords............................................................F-15
F.2.1.5 Logging in as new user............................................................F-16
F.2.1.6 Rebooting the RCU .................................................................F-16
F.2.2 Data logging ............................................................................................F-18
F.2.3 Error logging............................................................................................F-20
F.2.3.1 Error log descriptions...............................................................F-25

Contents vii
Appendix G Reference
G.1 Compensation equation overview ........................................................................ G-2
G.1.1 Encoder compensation............................................................................. G-2
G.1.1.1 Definition of position terms........................................................G-2
G.1.1.2 Definition of compensation terms..............................................G-3
G.1.2 Laser compensation................................................................................. G-5
G.1.2.1 Definition of position terms........................................................G-5
G.1.2.2 Definition of compensation terms..............................................G-6
G.2 Air refraction compensation.................................................................................. G-9
G.3 Worked example – laser compensation............................................................. G-11
G.3.1 Direction sense setting........................................................................... G-11
G.3.2 Laser dead path (LO)............................................................................. G-12
G.3.3 Workpiece thermal expansion compensation (αw, Twc, WO).................. G-12
G.3.4 Machine structure thermal expansion compensation (Tsc, S)................ G-12
Appendix H Test records
H.1 Installation and configuration checklist..................................................................H-2
H.2 Installation details..................................................................................................H-3
H.3 Sensor record/test sheet .......................................................................................H-5
H.4 Parameter table record sheets..............................................................................H-7

viii Contents
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System overview 1-1
Section 1
System overview
Contained in this section
1.1 Introduction............................................................................................................ 1-2
1.2 System overview.................................................................................................... 1-2
1.3 Compensation functions........................................................................................ 1-4
1.3.1 Scale factor ............................................................................................... 1-4
1.3.2 Air refractive index compensation............................................................. 1-4
1.3.3 Encoder thermal expansion compensation...............................................1-5
1.3.4 Workpiece thermal expansion compensation...........................................1-5
1.3.5 Structure thermal compensation ............................................................... 1-7
1.4 Operational functions............................................................................................. 1-8
1.4.1 Selectable parameter tables...................................................................... 1-8
1.4.2 Compensation buffering............................................................................ 1-8
1.5 System components.............................................................................................. 1-9
1.6 Installation procedure overview........................................................................... 1-11

1-2 System overview
1.1 Introduction
This manual covers the installation, configuration and operation of the Renishaw RCU10
real-time quadrature compensator system.
1.2 System overview
The RCU10 real-time quadrature compensation system overcomes environmental error
sources in linear motion systems to improve process accuracy and repeatability. The
RCU10 monitors a machine’s ambient environment, via a network of sensors, and uses
advanced digital signal processing to perform real-time compensation on the position
feedback signals.
The RCU10 can provide:
Refractive index compensation, for laser encoders, using air pressure and
temperature sensors.
Scale thermal expansion compensation, for incremental linear encoders, using
material temperature sensors.
Thermal expansion compensation of machine structure and workpieces, using
material temperature sensors.
Format conversion – digital (A quad B) to analogue (Sin/Cos)
Scale factor conversion – laser wavelength to engineering units
Figure 1.1 – RCU10-P with sensors

System overview 1-3
A functional block diagram of the RCU10 is show below:
Figure 1.2 – Internal block diagram of operation when used in conjunction with a
laser encoder
The RCU10 processor accepts digital quadrature, along with the environmental data
collected by factory-calibrated sensors, and calculates the total amount of compensation
necessary to correct the axis position. The required compensation is then applied through
quadrature scaling and injection (addition or removal of quadrature pulses) into the
encoder feedback signal, the total process being completely transparent to the motion
controller. The corrected feedback signals are provided to the motion controller in either
RS422 digital A quad B or analogue Sin/Cos 1 Vpp formats, with a nominal accuracy of
±1 ppm (refractive index only) or ±2 ppm (with 10 ppm/°C material compensation).
The RCU10 compensator is available in two models:
RCU10-P, which contains an internal air pressure sensor
RCU10, which does not contain an air pressure sensor
One compensator is required for each machine axis that is to be compensated.
When laser encoders are being used, one compensator in the system must be an
RCU10-P so that the ambient air pressure can be determined and refractive index
compensation applied. The basic RCU10 may be used for conventional (non-laser)
encoders or for ‘slave’ axes in a laser encoder system.

1-4 System overview
When used as a multi-axis system, the RCU10s are linked via a high-speed serial link;
this allows the RCU10s to share sensor information and operating data.
Figure 1.3 – Multi-axis system
1.3 Compensation functions
The RCU10 is capable of performing a number of processing functions on position
feedback signals. These compensation modes can be enabled or disabled, depending on
the application requirements and type of encoder used. The following section provides an
overview of these modes. Full details can be found in Appendix G.
1.3.1 Scale factor
The RCU10 is capable of performing a fixed scale factor correction to convert the intrinsic
encoder resolution into a more useable value (e.g. 633 nm -> 1 µm). The scale factors
available depend on the input resolution and the type of output required.
This is the basic mode of operation when no compensation functions are enabled.
1.3.2 Air refractive index compensation
Air refractive index (wavelength) compensation is applied according to the environmental
values received from the air temperature and pressure sensors. This mode of
compensation is used with laser encoders to provide a consistent and accurate feedback
signal regardless of current environmental conditions.

System overview 1-5
Since the wavelength of light is a function of the ambient conditions local to the beam
path, without compensation errors can incur. This error is of the order of 1 ppm for each
of the following changes in environmental conditions:
1 °C (≈1.8 °F) Change in air temperature
1 ppm for every 3.3 mbar (≈0.1 in/Hg) Change in air pressure
30% RH @ 40 °C Change in relative humidity
Air temperature sensors are provided to monitor any local temperature variation within the
boundaries of the machine. An air pressure sensor is built into the compensator unit
(RCU10-P model only). Humidity is assumed to be relatively constant, and a fixed value
may be entered via the configuration software.
To enable the RCU10 system to perform in real time, each of these sensors is read, and
the related computation (Edlen’s equation*).
* See Appendix G
1.3.3 Encoder thermal expansion compensation
When using conventional scale encoders, the positional accuracy of the system will
depend on the thermal expansion of the scale substrate material. The RCU10 is capable
of compensating for this effect by measuring the temperature of the scale and applying
the relevant positional correction. This will significantly improve system accuracy when
subjected to temperature variation.
To utilise this compensation mode, a material temperature sensor must be placed on the
scale substrate material and the RCU10 configured with the scale’s coefficient of thermal
expansion (CTE) and the distance between the machine home and expansion origin
position.
1.3.4 Workpiece thermal expansion compensation
The system can also perform material thermal expansion compensation. The function of
this feature is to track workpiece temperature and perform compensation based on its
CTE, such that the axis position is modified in real time to produce a part with the correct
dimensions for current environmental conditions.
To utilise this compensation mode, a material temperature sensor must be fitted to either
the part being machined, or a part of equivalent thermal characteristics. A reference
location, from which the workpiece is expected to expand, should be identified (by
consideration of part fixturing method etc). Once workpiece compensation is enabled, the
machine position will be modified to account for workpiece expansion relative to this
reference location.

1-6 System overview
Workpiece expansion concept
The size of a workpiece is proportional to its CTE and the ambient temperature. One of
the major sources of error in large parts can be ‘feature misplacement’, which can result
from thermal expansion or contraction of the part.
Consider two matching workpieces – one made at 30 °C (86 °F) and one made at 20 °C
(68 °F). If these parts are machined without workpiece expansion compensation applied,
they will not be the same size when brought together at the same temperature (the part
made at the higher temperature will be smaller than the one made at the lower
temperature).
By constantly monitoring the workpiece temperature, the RCU10 can use its CTE to
calculate the expansion that has occurred relative to a nominal reference temperature of
20 °C (68 °F). This process ensures that parts machined in a poorly controlled
environment will be as accurate and consistent as parts machined in an environment
maintained at 20 °C (68 °F). That is to say, no matter what temperature the part is
machined at, it will be the correct size when measured at 20 °C (68 °F).
Expansion is a greater problem in large workpieces because the amount of expansion is
proportional to the distance from the reference point. For example, at a point 40 m
(≈130 ft) from the reference point on an aluminium workpiece at 30 °C (86 °F), the error
will be 8 mm (5/16 in).
New
‘expanded’
size
Reference point,
centre of the
workpiece Anchor
point
Expanded
size
Expansion is forced in
these directions, away
from the anchor point
Figure 1.4 – Workpiece expansion
Workpiece compensation reference point
It is up to each user to establish a reference point suitable for their specific workpiece and
application. Some experimentation may need to be carried out in order to determine how
each fixture or workpiece behaves and thus the best way to apply compensation.
The process of defining a reference point can be complex and depends on many factors.
It is up to the user to decide on the best jigging and anchoring options for the workpiece.

System overview 1-7
Expansion coefficients
The RCU10 recognises expansion coefficients as parts per million per degree Celsius or
degree Fahrenheit (the unit of temperature used depends on how the user configures the
system). The reference temperature for material expansion is 20 °C (68 °F).
Table 1.1 below shows example expansion coefficients for aluminium and steel:
Table 1.1 – Expansion coefficients
Material ppm/°C ppm/°F
Aluminium 20 11.11
Steel 10 5.56
Use the following formula to convert from ppm/°C to ppm/°F:
[ppm/°C] multiplied by 5/9 = [ppm/°F]
e.g. 20 ppm/°C x 5/9 = 11.11 ppm/°F
1.3.5 Structure thermal compensation
An additional source of positioning error may be the thermal distortion of the machine
structure. This could manifest in a number of ways including:
expansion of the spindle
expansion of the machine structure
As long as the thermal effect is linear and not related to axis position, the RCU10 can be
used to reduce the error.
To utilise this compensation mode, a material temperature sensor must be placed on the
applicable part of the machine structure and the RCU10 configured with the number of
micrometres of correction required per degree C.

1-8 System overview
1.4 Operational functions
A number of useful operational functions (some optional) are available on the RCU10 to
provide flexibility and ease of use.
1.4.1 Selectable parameter tables
A number of ‘parameter tables’ are available for use during operation, which are
selectable through external I/O. These allow easy ‘switching’ of a number of common
options/operations, including:
Dead path or reference offset from scale expansion origin
Workpiece temperature sensor
Workpiece expansion coefficient
Workpiece origin offset
Workpiece origin type
The use of these switchable parameters allows numerous functions such as:
Multiple machine home positions
Changing to an alternative machining zone
Use of multiple workpiece material sensors (for multiple machine zones or other
reasons)
Changing of the material type (e.g. aluminium/steel)
1.4.2 Compensation buffering
When the RCU10 is in this mode, it will continue to monitor the encoder input and perform
the relevant quadrature scaling. However, any injection required to maintain compensated
position will be stored in a buffer within the RCU10. When the mode is disabled, any
stored (buffered) count is slowly injected into the motion feedback loop and the fully
compensated position re-established. The rate at which this compensation is injected is
user-configurable.
This function is useful where an axis needs to be temporarily disabled, but the original
position recovered at a later time. For example, some machines have an Emergency Stop
button that can be used to temporarily stop machine operation, but continue after it is
released without having to re-home the machine. In this case the injection compensation
is buffered, preventing any movement during the ‘E-stop’ period which would cause a
following error on the machine controller.

System overview 1-9
1.5 System components
The following provides a brief overview of the main system components:
Compensation unit with internal air pressure sensor
(part number: RCU10-PX-XX)
Powered from 24
V dc, the RCU10-PX-XX contains the
digital signal processor based compensation electronics and
an
internal air pressure sensor. For applications that use a
laser encoder and require refractiv
e index compensation, the
RCU10
-PX-XX unit is a requirement. In multi-axis
applications, only one RCU10
-PX-XX is necessary because
compensation for additional axes is provided by
RCU10
-XX-XX units (detailed below). In these applications,
the pressure senso
r reading is distributed to other RCU10s in
the network via a high-speed serial link.
Compensation unit (part number: RCU10-XX-XX)
Similar to the RCU10
-PX-XX, however this assembly does
not contain a pressure sensor.
Note that one RCU10 compensation un
it is required for each
axis to be compensated. For example, a three
-axis laser
encoder based system would need:
1 off RCU10-PX-XX
2 off RCU10-XX-XX
and a three
-axis tape or glass scale encoder system would
need:
3 off RCU10-XX-XX
Air temperature sensor (part number: RCU10-AT-XX)
The air temperature sensor is used in applications that
require refractive index compensation. The sensor contains a
calibrated thermistor to monitor ambient air temperature in
the range of 0 °C to 40 °C. The temperature readin
g is
converted into a digital signal inside the sensor, which
reduces susceptibility to noise when the reading is
transmitted to the RCU10.