WATT PILOT

WATT PILOT
WATT PILOT
Motorized Attenuator
USER MANUAL
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Table of Contents
1. Introduction ............................................................................................................. 3
1.1. Watt Pilot short description ................................................................................ 3
1.2. General safety requirements ............................................................................. 3
1.3. Operating and storage conditions ..................................................................... 3
2. Operation principle ................................................................................................. 4
2.1. Watt Pilot main components .............................................................................. 4
3. Assembling ............................................................................................................. 5
4. Watt Pilot control software .................................................................................... 6
4.1. Software installation ........................................................................................... 6
4.2. First steps ............................................................................................................ 7
4.4. Keyboard shortcuts............................................................................................. 9
4.6. Command set .................................................................................................... 12
5. “Watt Pilot” controller features (TTL controller) ................................................. 13
5.1. Input signal requirements for TTL version controller. .................................... 14
5.2. Input signal timing for TTL version controller ................................................. 14
6. Watt Pilot electrical/mechanical characteristics ................................................ 16
7. Mechanical dimensions. ...................................................................................... 17
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1. Introduction
This manual is designed to help to install and operate Watt Pilot. This manual is
a part of the product. Please read instructions of installation and operation
carefully, before installing and operating Watt Pilot. Safety instruction must be
read especially careful. If there is any questions about contents of this manual
please contact Altechna. Altechna reserves the right to update contents of the
manual without notification.
1.1. Watt Pilot short description
Motorized Watt Pilot is a computer controlled laser beam attenuation device. It
attenuates free space laser beam/pulse continuously without introducing
additional energy fluctuations. Watt Pilot is essential in systems, where stable
laser power adjusting is necessary. User friendly software “ALT-Step” or “SCA”
are recommended to control Watt Pilot via PC.
1.2. General safety requirements
Motorized Watt Pilot is designed to operate in conjunction with laser system. All
applicable rules and regulations for safe operation of lasers must be known and
applied while installing and operating Watt Pilot. The customer is solely
responsible for laser safety while using Watt Pilot as standalone or integrated
into system. The customer must use suitable protective measures.
While assembling or operating Watt Pilot, cannot be stared into direct or
scattered laser beam. All parts of the body must be kept away from the laser
radiation. While adjusting laser beam path through Watt Pilot laser power must
be low as possible. The risk of hazardous laser radiation can increase while
optical components or instruments are used in combination with Watt Pilot.
Appropriate eye protection must be worn at all times.
Electrical safety requirements must be complied while assembling and
operating Watt Pilot.
1.3. Operating and storage conditions
Environmental conditions that must be hold while storing, servicing and
operating are:
Storage temperature should be between -35 °C and +6 0°C. Operating
temperature is 25 °C ± 10 °C. Watt Pilot must be pr otected from humidity, dust
and corrosive vapors to avoid damaging optical components and electronics.
Avoid strong static electricity and electromagnetic fields.
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2. Operation principle
Figure 1. Watt Pilot principle of operation. Color differences shows intensity of
laser beam. Brighter red means more intensive laser beam.
The Motorized Watt Pilot incorporates 2 high-performance brewster type thin
film polarizers, which reflect s-polarized light while transmitting p-polarized light.
Rotating phase retardation of λ/2 waveplate is placed in the incident polarized
laser beam. The intensity ratio of those two beams may be continuously varied
without alteration of other beam parameters by rotating the waveplate. The
intensity of either exit beam, or their intensity ratio, can be controlled over a
wide dynamic range. P-polarization could be selected for maximum
transmission, or high-purity s-polarization could be reflected when maximum
attenuation of the transmitted beam takes place. Proper functioning of Watt Pilot
requires optimal configuration of optical elements regarding to incident laser
beam. Watt Pilot output polarization contrast depends on incident laser beam
polarization contrast. Higher incident laser beam polarization contrast, leads to
higher Watt Pilot output polarization contrast.
2.1. Watt Pilot main components
Optical components are placed into mechanical holders. Main mechanical
components of motorized Watt Pilot are shown in figure 2. Waveplate mount is
designed to 1 inch diameter waveplate λ/2.
Figure 2. Main components of Watt Pilot.
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Wave plate mount is attached to micro step motor. Waveplate inside the
waveplate holder is rotating around the optical axis of incident laser beam.
Micro step motor and waveplate mount are shipped together in one piece, if
there is no other request. Brewster type thin film polarizers are placed into
adapter for polarizers. Polarizers to the mount are fixed using 4 plastic bolts.
Adapter for polarizers and waveplate mount are fixed while using M4 screw with
vinyl cap. Watt Pilot might be fixed to an optical table using posts and clamps or
to the custom system while using M6 screw on the bottom.
3. Assembling
Figure 3. Assembling the Watt Pilot.
Watt Pilot assembling steps:
Step 1 Place polarizers into mechanical adapter. Polarizers must face each
other with surfaces coated with polarizing coating. Polarizing coating is
marked with an arrow, so you have to put the polarizers with the
arrows on the sides facing each other. Then fix polarizers with the
plastic bolts (use all 4 plastic bolts to fix one polarizer).
NOTICE: do not tighten up the bolts too much since it can bend the
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polarizer and thus distort the laser beam.
Step 2 Put wave plate into attenuator between two mounting rings as shown.
Be sure the wave plate is immobilized tightly.
Step 3 Attenuator consists of two mechanical parts. You should assemble
both mechanical parts together.
Step 4 Use fixing screw for tightening both parts together.
PEASE NOTICE: Powder free gloves must be worn while mounting optical
components. Avoid touching and scratching optical surfaces.
4. Watt Pilot control software
USB version controller of Watt Pilot can be controlled via computer using “ALTStep” software Watt Pilot control software is the automated laser power
attenuator solution.
Main features:
I. Simple stand-alone
controller.
II. User – friendly
software interface.
III. High precision.
IV. Simple text – based
communication
protocol.
V. Easy to integrate.
4.1. Software installation
Launch WattPilotSetup.exe (from USB stick) program to install control program.
Please notice that if you don't have Windows Framework installed, you will be
prompted to do that. Windows Framework can be downloaded from Microsoft
web page automatically or, alternatively, it can be found a copy in USB stick (file
dotnetfix.exe).
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4.2. First steps
Main window of Watt Pilot software is called “Attenuator” and shown in figure 5.
In this window there are controls to set energy, open Configuration and Direct
Control dialogs. Using Direct Control dialog user can directly enter position in
steps for the stepper motor as shown in figure 6.
Figure 5. Main window of “WattPilot”.
Figure 6. Direct control dialog.
Energy that can be changed in main window (figure 5) can be determined using
equation (1):
௠௜௡ ௠௔௫ ௠௜௡ ∗ cos ∗ ଶ
(1)
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Emin is the minimal energy, Emax is the maximal energy, k is the steps per degree
ratio, and x is current position in steps. Calibration procedure is described in
chapter “IV.I. Configuration”.
4.3. Configuration
Configuration dialog (figure 7) allows calibrating attenuator and changing some
basic program parameters.
Figure 7. Configuration dialog.
Minimal energy Emin and maximal energy Emax values should be measured
directly. Coefficient k is number of stepper motor steps degree and is provided
together with attenuator specification. Position in steps should be zero when
E=Emax. Use “Set current position as home” to reset current position value.
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Calibration and stepper parameters:
Energy unit – short name of the energy units used.
Serial port – serial port of the PC that is connected to the controller of “Watt
Pilot”.
Acceleration – acceleration of stepper motor when motion is started.
Deceleration – deceleration of stepper motor when motion is finishing.
Standby power – Power applied to the motor when it is not moving. It is
necessary to decrease the applied power level in order to avoid stepper motor
overheating.
Motion power – power applied to the motor while moving.
4.4. Keyboard shortcuts
For quick manual position tuning several keyboard keys were mapped to the
following characters:
Increase position single step: u
Decrease position single step: j
Increase position 10 steps: i
Decrease position 10 steps: k
Increase position 100 steps: o
Decrease position 100 steps: l
4.5. Controlling “Watt Pilot” using “HyperTerminal”
For “Windows Vista” and “Windows 7” “HyperTerminal” emulator could be used.
For example: “Indigo Terminal Emulator”. First of all COM port used by Watt
Pilot soft must be known. Procedure described below and shown in picture 8.
Right click My Computer (1) → Properties (2) → Device Manager (3) → Ports
(COM & LPT) (4). Find a port called USB Serial Port in the list (Watt Pilot
controller box must be connected to PC). Remember the number of this port
(e.g. COM9). Number of this port is needed also while working with “WattPilot”
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Figure 8 Finding out which USB port is used by Watt Pilot.
If “Windows XP” is used “HyperTerminal” can be found:
Start -> All Programs -> Accessories -> Communications -> HyperTerminal.
If “HyperTerminal” emulator is used, please launch from location where it is
installed.
When clicked on “HyperTerminal”, window shown in figure 9 appears.
Figure 9. “HyperTerminal” connection window.
In window shown in figure 9 please write in random name and click “OK”.
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Figure 10. Choose COM port used by “Watt Pilot”.
In window shown in figure 10 please choose COM port used by “Watt Pilot”.
Figure 11. COM port properties window.
In COM port dialog window please choose “Bits per second” = 9600 and “flow
control” = None and click “OK”.
Window shown in figure 12 appears. Press connect button (red circle) if
needed. Type commands to "hyper terminal" window. Commands are listed in
chapter “IV.IV. Command set”.
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Figure 12. HyperTerminal control window.
4.6. Command set
Notation: <n> - integer number (0-255), <a> - axis name: X, Y, or Z. Text in
Bold font means the string sent to or received from controller. Communication
protocol is text – based and is case – sensitive. Command is delimited by new –
line symbol \n\r. One command line is follower by one response line. No data
should be sent until response to the command is received. Response line starts
with OK if command was executed successfully otherwise ERR followed by an
error message is sent. Commands are described in table
Table 1. Command list.
Command
p
Responce
OK a=<n> d=<n>
s=<n>
wn=<n>
ws =<n>
a<n>
OK
d<n>
OK
s<n>
OK
wm<n>
OK
ws<n>
OK
Description
Show current parameter values. a –
acceleration, d – deceleration, s – speed, wm
– motion mode power, ws – standby mode
power.
Set acceleration parameter and store new
value in permanent memory.
Set deceleration parameter and store new
value in permanent memory.
Set speed parameter and store new value in
permanent memory.
Set motor power value <n> (1-255) for
motion mode and store new value in
permanent memory.
Set motor power value <n> (1-255) for
standby mode and store new value in
permanent memory.
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o
h<a>
m<a><n>
g<a><n>
OK X=<n> Y=<n> Show current X, Y, Z coordinates.
Z=<n>
OK
Set current position for axis <a> as home
position.
OK X=<n> Y=<n> Move <a> axis <n> steps relatively to the
Z=<n>
current
position.
Response
includes
coordinates after motion was finished.
OK X=<n> Y=<n> Move <a> axis to the absolute position <n>.
Z=<n>
Response includes coordinates after motion
was finished.
5. “Watt Pilot” controller features (TTL controller)
Figure 8. Watt Pilot controller (TTL controller version).
Features:
• Half stepping.
• Galvanic isolated inputs.
• 3.3 V and 5 V tolerant inputs.
• Input clock/step frequency up to 2000 Hz
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5.1. Input signal requirements for TTL version
controller.
Controller inputs are optocoupled, it means there are no galvanic connection
between power supply and signal source. This eliminates any motor generated
electrical noise and allows simple controller installation. However this requires
slightly more current from source, but majority of microcontrollers/fpga are able
to drive LED of optocouple directly. Input circuit is shown in the figure below. To
reduce 5 V logic current, resistors of 180 Ohm can be added in series with
STEP and DIR lines. 4 and 5 pins are connected to mechanical zero position
switch directly. Some debouncing circuit may be considered if zero switch is
used, for example a capacitor in parallel with switch. Switch is closed if in zero
positions.
To control logic
Figure 9. Circuit diagram of input section
Table 2. Input signal electrical characteristics.
Parameter
MIN
Input voltage, high level
2.8
TYPICAL
Input voltage, low level
Input current: @ 2.8 V
4.6
@ 3.3 V
5.2
@
6.8
5V
MAX
UNITS
5.5
V
2.3
V
mA
5.2. Input signal timing for TTL version controller
Motor turns one step after rising edge of STEP signal. Proper DIR voltage must
be applied before rising edge (time tDIR1). Rise/Fall times of signals do not
matter if there are used timings, shown in the diagram below. Grayed parts in
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DIR timeline show moments then DIR level do not matter, can be changed and
white slots show when DIR level must be kept stabilized.
It is necessary to mention that motor shaft is inert. Frequency of STEP signal
must be controlled linearly, especially at high motor speeds. Motor should
accelerate and decelerate smoothly. For instance, control logic must sweep
down STEP frequency before changing DIR level. Similarly, frequency must be
swept up then reaching high motor speed.
Figure 10. Input signal timing. It is considered that DIR signal is always kept high in this
example and angle is increasing on every STEP rising edge.
Table 3. Input signal timing (parameters may vary depending on Watt Pilot version).
SYMBOL
tstepLOW
tstepHIGH
tstepPeriod
tDIR1
tDIRW
rresponse
DESCRIPTION
STEP low level duration (0 V)
STEP high level duration
(2.8 V – 5 V)
STEP period (determined by
motor)
Time to prepare DIR level
before STEP rising edge
DIR pulse width
Delay between STEP rising
edge and current applied to
motor windings
MIN
30
MAX
-
UNITS
µs
400
-
ns
0.5
-
ms
30
-
µs
30.4
-
µs
-
30
µs
5.3. Watt Pilot electrical connections for TTL controller
version.
Figure 11 and figure 12 shows locations of electrical connection. Watt Pilot is
controlled by a 9 pin D-SUB female connector.
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Input connector pins:
1. Common Cathode
2. DIR
3. TEMP
4. Zero position
switch
5. Zero position
switch
Power supply
connector pins:
1. Internal pin “+”.
2. External pin “-“.
Figure 11. Input and power supply connectors.
Figure 12. Motor connector and pin out.
6. Watt Pilot electrical/mechanical characteristics
Watt Pilot electrical and mechanical characteristics are shown in table 3.
Table 4. Electrical/mechanical characteristics.
PARAMETER
VALUE
UNITS
λ/2 Waveplates Holder Angular Resolution
0.01125
deg/step
Steps Per full Turn
32000
steps
Controller Step Response time, response*
30
µs
Maximum Frequency of STEP Signal**
2000
Hz
Maximum Controller Power supply Voltage
10
V
* Delay between STEP signal rising edge and current applied to motor windings, see table 3.
** Step frequency can be increased by using more powerful power supply. Considering our
motor performance, noise and heat dissipation, 5 V / 1.2 A power supply is optimal
Parameters may vary depending on which controller is used.
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7. Mechanical dimensions.
Figure 13. Mechanical dimensions of Watt Pilot.
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