Lightware SF20 User manual

LW20 / SF20 LiDAR sensor
Product manual
Table of contents
LW20 / SF20 LiDAR - Product manual - Revision 7 | of | © LightWare Optoelectronics (Pty) Ltd, 2018 | www.lightware.co.za1 28
The
compact
LiDAR sensor
for drones,
autonomous vehicles
and robots
Features:
•Small size laser rangefinder when weight and size are critical
•Long range measurements up to 100 meters to sense remote objects
•Up to 388 readings per second for fast detection of obstacles
•IP67 enclosure prevents damage from water and dust
•Built-in drivers to make a scanning LiDAR by adding a digital servo
•Encoded laser pulses prevent interference for other lasers
•First and last return signals are available to suit your application
•Power saving mode to save energy when not in use.

LW20 / SF20 LiDAR sensor
Product manual
Table of contents
Table of figures
Figure 1 :: Measuring exact height above ground 3......................................................................................................
Figure 2 :: Collision avoidance zones 3.....................................................................................................................
Figure 3 :: Autonomous vehicle navigation 4..............................................................................................................
Figure 4 :: Connection to a USB converter cable 6........................................................................................................
Figure 5 :: Setting the baud rate for LW20 communications 6..........................................................................................
Figure 6 :: The graphical interface Home screen 7.......................................................................................................
Figure 7 :: The graphical interface Setup screen 7.......................................................................................................
Figure 8 :: The graphical interface Parameters screen 8................................................................................................
Figure 9 :: The graphical interface Operate screen 8....................................................................................................
Figure 10 :: Connection to a USB converter cable 9.....................................................................................................
Figure 11 :: Setting the baud rate for LW20 communications 9........................................................................................
Figure 12 :: Arrangement of screens in terminal emulation mode 10.................................................................................
Figure 13 :: Connection to a Devantech USB-ISS module 11.............................................................................................
Figure 14 :: The LightWare Terminal application top level window showing the toolbar 11.......................................................
Figure 15 :: Selecting the Devantech I2C-ISS converter 11..............................................................................................
Figure 16 :: I2C test dialog box showing command buttons 12.........................................................................................
Figure 17 :: Initial setup using the GUI or terminal emulation 14......................................................................................
Figure 18 :: Servo connections 15...........................................................................................................................
Figure 19 :: Setting up the electrical and mechanical characteristics of the servo 15.............................................................
Figure 20 :: Setting the servo’s limits of motion using the PWM values 16...........................................................................
Figure 21 :: Setting the servo’s PWM scale 16.............................................................................................................
Figure 22 :: Setting up the servo’s scanning characteristics 17........................................................................................
Figure 23 :: The effect of servo lag with no correction and after applying a 2.5 degree correction 17.........................................
Figure 24 :: Reducing the field of view to avoid detecting the landing legs on a drone 18.......................................................
Figure 25 :: Uni-directional scanning for higher precision 18...........................................................................................
Figure 26 :: Setting the alarms to warn of nearby objects 19..........................................................................................
Figure 27 :: Setting two dimensional alarms 19...........................................................................................................
Figure 28 :: Laser radiation information and labels 20..................................................................................................
Figure 29 :: Dimension drawings of the LW20 and SF20 20..............................................................................................
Figure 30 :: Serial and power cable 21.....................................................................................................................
Figure 31 :: Pinout diagram 22...............................................................................................................................
Product ordering codes
Product ordering codes 2.....................................................................................................................................
1. Overview of the LW20 4...................................................................................................................................
2. What can the LW20 do? 4.................................................................................................................................
3. What are the main characteristics of the LW20? 5...................................................................................................
4. Specifications of the LW20 / SF20 7....................................................................................................................
5. How to communicate with the LW20 using the graphical interface 8.............................................................................
6. How to communicate with the LW20 using a terminal emulator 11...............................................................................
7. How to communicate with the LW20 using a controller 15..........................................................................................
8. How to do an initial setup of the LW20 16.............................................................................................................
9. How to set up a scanning LiDAR using a digital servo 17............................................................................................
10. How to set up the alarms 21.............................................................................................................................
11. Limitations 21..............................................................................................................................................
12. Instructions for safe use 22..............................................................................................................................
Appendix A :: Dimension drawings 22.......................................................................................................................
Appendix B :: Cables and connections 23...................................................................................................................
Appendix C :: Complete command set for machine-to-machine communications 24................................................................
Revision history 28..............................................................................................................................................
Model family
Model name
Model description
LW20
LW20/B (50 m)
LiDAR sensor with serial and I2C output, max 50 m
LW20
LW20/C (100 m)
LiDAR sensor with serial and I2C output, max 100 m
SF20
SF20/B (50 m)
Open frame LiDAR sensor with serial and I2C output, max 50 m
SF20
SF20/C (100 m)
Open frame LiDAR sensor with serial and I2C output, max 100 m
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LW20 / SF20 LiDAR sensor
Product manual
!
Disclaimer
Information found in this document is used entirely at the reader’s own risk and whilst every effort has been made to
ensure its validity, neither LightWare Optoelectronics (Pty) Ltd nor its representatives make any warranties with respect
the accuracy of the information contained herein.
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LW20 / SF20 LiDAR sensor
Product manual
1. Overview of the LW20
The LW20 LiDAR is a compact laser rangefinder for use on drones, self-driving vehicles and robots. It
is designed to connect to many different processors using a serial or I2C protocol and runs from a
single 5 V power source.
The LW20 LiDAR offers professional grade performance in a tiny form factor. It can be used as a
distance measuring sensor or attached to a servo to create LiDAR maps that sense the world as two
dimensional images.
Measurements can be made to target surfaces up to 100 meters away in sunlit conditions. In
scanning mode up to 388 measurements can be made each second. The data can be streamed from
the communication ports or analysed internally to look for potentially hazardous alarm conditions.
The LW20 is also available as an open frame module for OEMs using part code SF20.
2. What can the LW20 do?
The LW20 can be used as an altimeter on multi-copter drones to measure the exact height above ground level or to set off alarms
when the ground gets too close.
Figure 1 :: Measuring exact height above ground
With a servo attached, the LW20 becomes a low cost, lightweight collision avoidance sensor.
Figure 2 :: Collision avoidance zones
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Product manual
Used on autonomous vehicles, the LW20 can be a forwards looking obstacle sensor or can be used to create “SLAM” maps to aid in
navigation.
Figure 3 :: Autonomous vehicle navigation
What’s your application?
3. What are the main characteristics of the LW20?
There are two models available, the LW20 and the SF20. The LW20 is a sealed unit suitable for
outdoor applications. It can easily be added onto existing products.
The SF20 is an open unit suitable for clean and dry applications or as an OEM component that is
built-in as standard equipment.
The LW20 housing measures 20 mm x 30 mm x 35 mm.
The SF20 assembly measures 20 mm x 30 mm x 32 mm.
The LW20 is waterproof to IP67 standard. It can be submerged in water to a depth of 1 meter
for 15 minutes and is protected against dust ingress.
Please note that the SF20 is not waterproof.
The LW20 weighs less than 20 grams (excluding cables). This makes it ideal for applications
where the low weight and small size are important.
The open frame SF20 weighs less than 10 grams. Use this module when low mass is the defining
specification.
The power supply, communications and servo driver signals are connected to the LW20 / SF20
using the built-in cable.
The cable has a shield that should be earthed to reduce electrical interference.
The power supply voltage must be between 4.5 V and 5.5 V and the LW20 draws about 110 mA
while measuring.
It is good practice to make sure that the power supply is able to deliver more current than
need and to make sure that the voltage is stable and clean from spikes.
The LW20 has a maximum measuring range of 100 meters with a resolution of 1 centimeter.
The accuracy of each measurement is ±10 centimeter.
New measurements are updated at a preset rate from a slowest of 48 readings per second to a
maximum of 388 readings per second.
The slower speed measurements give better measuring range and are useful for laser
altimeters or static distance measurements. The faster speed measurements are better for
scanning applications when the LW20 is attached to a servo.
The LW20 uses a laser to take time-of-flight measurements. The laser is rated Class 1M. Do not
view the laser with magnifying optics such as microscopes and telescopes.
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SF20 LW20
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Product manual
The LW20 is able to measure the first and last return signals when there is more than one
object in the laser beam.
Measuring the distance to the nearest object and the furthest object allows a drone to get
information about potential collisions with trees while simultaneously following the terrain at a
known height above ground.
The LW20 incorporates a laser encoding system that allows units to uniquely identify their own
signals. This prevents interference from other lasers that may be aiming at the same target
surface and makes it possible to run side-by-side redundant systems in safety critical
applications.
There are three different ways to communicate with the LW20:
•For machine-to-machine communication there is a built-in command set that uses ASCII
mnemonics. These commands work via the serial or the I2C ports.
•For human-to-machine communication there is an internal menu system that can be
accessed using a generic terminal application via the serial port. The LightWare Terminal
application can be used for this.
•For interactive and graphical communication there is a GUI based Terminal application
available from the LightWare website. This application also uses the serial port.
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LW20 / SF20 LiDAR sensor
Product manual
4. Specifications of the LW20 / SF20
LW20/B (50 m)
LW20/C (100 m)
SF20/B (50 m)
SF20/C (100 m)
Weight
20 g (excluding cables)
20 g (excluding cables)
10 g (excluding cables)
10 g (excluding cables)
Range
0.2 … 50 m (sunlit white
wall, 45 readings per
second)
0.2 … 100 m (sunlit white
wall, 45 readings per
second)
0.2 … 50 m (sunlit white
wall, 45 readings per
second)
0.2 … 100 m (sunlit white
wall, 45 readings per
second)
Resolution
1 cm
1 cm
1 cm
1 cm
Update rate
48 … 388 readings per
second
48 … 388 readings per
second
48 … 388 readings per
second
48 … 388 readings per
second
Accuracy
±10 cm
±10 cm
±10 cm
±10 cm
Outputs & interfaces
Serial and I2C (3.3 V)
Serial and I2C (3.3 V)
Serial and I2C (3.3 V)
Serial and I2C: 3.3 V
Power supply voltage
4.5 V … 5.5 V
4.5 V … 5.5 V
4.5 V … 5.5 V
4.5 V … 5.5 V
Power supply current
110 mA
110 mA
110 mA
110 mA
Laser power
<2 mW
<2 mW
<2 mW
<2 mW
Dimensions
19.5 mm x 30.2 mm x 35
mm, housing only
19.5 mm x 30.2 mm x 43
mm with cable gland
19.5 mm x 30.2 mm x 35
mm, housing only
19.5 mm x 30.2 mm x 43
mm with cable gland
19.5 mm x 30.2 mm x
32.1 mm
19.5 mm x 30.2 mm x
32.1 mm
Operating temp.
-30 .. +50°C
-30 .. +50°C
-30 .. +50°C
-30 .. +50°C
Approvals
FDA: 1710193-000
(2017/09)
FDA: 1710193-000
(2017/09)
FDA: 1710193-000
(2017/09)
FDA: 1710193-000
(2017/09)
Housing
Aluminium, ABS plastic
and glass
Aluminium, ABS plastic
and glass
ABS plastic and glass
ABS plastic and glass
Optical aperture
28 mm x 15 mm
28 mm x 15 mm
28 mm x 15 mm
28 mm x 15 mm
Beam divergence
0.3°
0.3°
0.3°
0.3°
Lens material
Glass
Glass
Glass
Glass
Connections
Wire tail, 5 core plus
shield
Wire tail, 5 core plus
shield
Wire tail, 5 core plus
shield
Wire tail, 5 core plus
shield
Enclosure rating
IP 67
IP 67
N/A
N/A
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LW20 / SF20 LiDAR sensor
Product manual
5. How to communicate with the LW20 using the graphical interface
To use the graphical interface to setup and test the LW20 you will need to connect the serial port of the LW20 to the USB port on a
PC. This is done using a serial-to-usb converter such as the TTL-232R-3V3-WE converter cable from FTDI (http://www.ftdichip.com/
Products/Cables/USBTTLSerial.htm). This converter provides both the signals and power supply to the LW20.
Figure 4 :: Connection to a USB converter cable
Once the converter is wired up to the LW20, prepare the Terminal application on the PC as follows:
•Download and instal the latest Terminal application from the LightWare website
•Open the Terminal application
•Select the “Laser” icon
•Set the baud rate to 115200
•You can tick the “Remember settings” box if you intend to use this configuration again
•Apply the change to close the dialog window
Figure 5 :: Setting the baud rate for LW20 communications
To establish communication between the LW20 and the graphical interface:
•Plug the LW20 converter into a USB port on the PC
•Click the “Connect” icon - a notice of the connection and its associated USB port number should become visible on the toolbar
•Press the “LW20” icon - this opens the graphical interface home screen
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There are four tabs at the top of the home screen. Each one provides a visualization of the settings inside the LW20 and guides you
through the setup process as follows:
•The “Home” tab shows the welcome screen with shortcuts to other screens shown near the bottom
•The “Setup” tab is for checking or entering settings with graphical indicators showing the effect of any changes
•The “Parameters” tab gives a tabulated summary of all the settings
•The “Operate” tab is a graphical display that shows the LW20 working with the settings that you have entered
Figure 6 :: The graphical interface Home screen
The “Setup” tab is divided into three functional areas. On the left there are four buttons that group related settings together. In the
middle column the names and values of each setting are shown in editable boxes. On the right of the screen there is a graphic
visualizing the group of settings.
The four Setup buttons have the following features:
•The “Laser” button is for settings that relate to distance measurement, communication and encoding
•The “Servo” button is to configure the physical parameters of servo chosen for scanning
•The “Sweep” button defines the software limits of the scan
•The “Alarm” button is used to create software controlled, two dimensional alarms
Figure 7 :: The graphical interface Setup screen
Details of each button and how to use the settings are given later in this manual.
Note that any settings changes are not automatically saved. The “Save” button must be pressed if you want to keep the changes.
The graphics can be manipulated to alter their position and angle of view using the left and right mouse keys. There is a scale slider
in the top right hand corner along with icons to return to the default isometric view or change to a view from above.
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The “Parameters” tab gives a summary of all the available settings, grouped into columns to match the buttons on the “Setup” tab.
This tab is useful to users who are familiar with effects of each setting and know what values to enter for their application.
Figure 8 :: The graphical interface Parameters screen
The “Operate” tab shows a graphic that can be used for display purposes. Different elements can be added or removed from the
image using the tick boxes and the view can be changed to represent either single point distance measurement or two dimensional
LiDAR scanning.
Figure 9 :: The graphical interface Operate screen
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6. How to communicate with the LW20 using a terminal emulator
To use a terminal emulation application to setup and test the LW20 you will need to connect the serial port of the LW20 to the USB
port on a PC. This is done using a serial-to-usb converter such as the TTL-232R-3V3-WE converter cable from FTDI (http://
www.ftdichip.com/Products/Cables/USBTTLSerial.htm). This converter provides both the signals and power supply to the LW20.
Figure 10 :: Connection to a USB converter cable
Once the converter is wired up to the LW20, prepare the Terminal application on the PC as follows:
•Download and instal the Terminal application from the LightWare website
•Other terminal emulation programs with the correct communication parameters will also work
•Open the Terminal application
•Select the “Laser” icon
•Set the baud rate to 115200
•You can tick the “Remember settings” box if you intend to use this configuration again
•Apply the change to close the dialog window
Figure 11 :: Setting the baud rate for LW20 communications
To establish communication between the LW20 and the Terminal application:
•Plug the LW20 converter into a USB port on the PC
•Click the “Connect” icon - a notice of the connection and its associated USB port number should become visible on the toolbar
•The LW20 is now running in machine-to-machine mode and will respond to the set of machine commands
•Press the <?> key followed by <CR>. The LW20 will reply with the product code, hardware revision and software revision
In this mode, the LW20 will respond to the command set normally used by a controller to communicate using either the serial or I2C
ports. The “?” command mentioned above is the command used to identify the LW20. The full command listing can be found in
Appendix C.
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Pressing the <ESC> key switches the LW20 into human-to-machine mode providing data and menus in an easy to read format. You can
navigate between the menus and live data streams using the arrow keys. There are four screens available, two show the LW20
setup and two show the setup of the servo if it is attached.
Figure 12 :: Arrangement of screens in terminal emulation mode
Each item on a menu screen can be selected and changed by pressing the number or letter adjacent to the description. Some of the
values are numeric while others will toggle between the available options. Note that any changes made here are stored immediately
in permanent memory and will remain valid after the power is removed.
The columns on the live data screens show the distances (first and last signals) and alarm status. The live data screen associated
with the servo setup also includes the aiming angle of each reading in the first column.
Pressing the <±> or <~> key switches back into machine-to-machine mode.
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6.1 How to communicate with the LW20 using the Devantech USB to I2C module
Figure 13 :: Connection to a Devantech USB-ISS module
The I2C interface is designed for machine-to-machine communications with multiple devices over a small network. In order to test
the I2C interface on the LW20, an I2C to USB converter can be connected and a limited number of commands can be sent to the LW20
using the LightWare Terminal application.
Figure 14 :: The LightWare Terminal application top level window showing the toolbar
Select the correct protocol using the “Settings” icon on the toolbar of the LightWare Terminal. This should match the I2C converter
being used and in this example the Devantech USB-ISS adaptor is shown.
Figure 15 :: Selecting the Devantech I2C-ISS converter
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Once the correct setting is applied, commands can be sent and results viewed by selecting the “I2C Tester” icon and pressing the one
of the test buttons available in the dialog box.
Figure 16 :: I2C test dialog box showing command buttons
The factory default I2C bus address is 0x66.
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7. How to communicate with the LW20 using a controller
The LW20 is designed to communicate with a host controller. This controller can be a single board computer, flight controller or a PC.
There are two communications interfaces available, serial and I2C. The LW20 and SF20 models both ship with a single serial and I2C
communication cable.
The serial port is a one-to-one protocol that lets a single LW20 talk to a single host controller. The serial interface uses 3.3 V logic to
transmit results and receive commands.
Multiple LW20’s with an I2C port can be connected onto an I2C bus. The I2C interface uses 3.3 V logic to receive commands from a
master device.
The communication language for both the serial and I2C ports is based on ASCII commands and messages. Command strings take the
form of simple mnemonics and results are provided as text strings.
A command string is made up of:
•A directive that indicates what action to take
• A channel that represents a functional block containing related information
• An index that determines which value is being acted on
•A numeric value if needed
•<CR><LF> indicates the end of the command
There are four different directives, each using a single ASCII character:
? Fetch a value
# Write a value
$ Stream live results
% Save changes
There are six channels available inside the LW20:
P The Product channel contains product related information
L The Laser channel contains all laser related information
S The Servo channel contains all servo related information
C The Communication channel handles serial and I2C data
A The Alarm channel provides alarm status information
E The Energy channel controls power usage
A typical command sent by the host controller would be:
?PN<CR><LF>
Which means: What is your Product Name?
The LW20 / SF20 would reply with:
PN:LW20 <CR><LF>
Which means: Product Name : LW20
Full details of the communication language are given in Appendix C.
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8. How to do an initial setup of the LW20
Using the GUI, Terminal or machine commands the measuring characteristics of the LW20 can be tailored to suit different
applications. The primary settings can be found by pressing the “Laser” button under the “Setup” tab of the GUI or on the main
menu screen of the terminal.
Figure 17 :: Initial setup using the GUI or terminal emulation
Details of the initial settings are given in the table below.
Setting name
Range of values
Description
Mode (update rate)
48 … 388 readings per second
Sets the rate at which distances are measured.
Zero distance offset
-10.00 … 10.00 meters
Moves the point at which the measured distance reads zero. This is to
correct for errors introduced by the mounting position.
Encoding pattern
None, A, B, C, D
Selects the encoding pattern of the laser to prevent interference from
other laser devices that might be aiming at the same target surface.
Lost signal confirmation
1 … 250
Sets the number of readings that must be taken before a lost signal or
out-of-range condition is reported. This value prevents brief losses of
signal from affecting the distance results.
Alarm A distance
0 … 100 meters
Sets the activation distance of alarm A. This is the distance below which
the alarm changes state from ‘0’ to ‘1’.
Alarm B distance
0 … 100 meters
Sets the activation distance of alarm B. This is the distance below which
the alarm changes state from ‘0’ to ‘1’.
Alarm hysteresis
0 … 10 meters
The alarm hysteresis prevents the alarms from switching rapidly between
states when the target surface is at the activations distance. Activation
occurs at the set distance minus the hysteresis distance and deactivation
occurs at the set distance plus the hysteresis distance.
Serial port baud rate
960 … 921600
Select the baud rate for the serial communication port. Note that new
values take effect after they are saved and power is cycled, the factory
default is 115200.
I2C address
0x00 … 0x7F
The address of the LW20 on the I2C bus, the factory default is 0x66.
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9. How to set up a scanning LiDAR using a digital servo
The LW20 can be converted into a scanning LiDAR by attaching it to a digital servo and using the built-in servo driver hardware and
software. The LiDAR data can be streamed live or used to activate two internal alarms. This makes a useful SLAM mapping device or
a collision sensor.
The servo driver works with most standard digital servos. Note that analog servos are not compatible as they respond too slowly to
the control signals produced by the LW20. The LW20 is connected to the servo as shown in the diagram below:
Figure 18 :: Servo connections
To reduce the chances of power supply spikes affecting the performance of the LW20, it is important to run the servo from a
separate power supply. Check the servo specifications for the correct voltage and current ratings and make sure that there is a
common connection to the negative rails of the LW20 and servo power supplies.
Communications to the LW20 and the servo can be made through either the serial port or via an I2C bus. In this guide we will use the
serial port and the GUI interface to set up the servo parameters and configure automatic scanning.
Select the ”Servo” button under the “Setup” tab to access the initial servo configuration graphic.
Figure 19 :: Setting up the electrical and mechanical characteristics of the servo
With the LW20 connected to the GUI, settings can be entered and saved even without the servo attached. This is useful if you already
know what values to enter for your chosen servo. If the servo is connected, then ticking the “Connected” box and entering settings
through the GUI will result in live movements of the servo, allowing you to see the effect of the new values.
The servo position is controlled by a pulse-width modulated (PWM) signal coming from the blue control line of the LW20. This signal
can change in width from 0us to 3000 us in steps of 0.7us and updates 333 times per second. A given servo will be limited to a
specific range of PWM widths, corresponding to the physical limits of rotary motion.
By default the minimum PWM width is set to 1000 us and the maximum PWM width to 2000 us. This is suitable for most servos but
new values can be entered if needed. If a new value beyond the capabilities of the servo is entered, the servo may draw too much
power, get hot or buzz.
CAUTION: Setting PWM values outside the specified range of the servo may cause damage to the servo.
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When viewed from above, the lower PWM setting turns the servo shaft to the extreme left position and the higher PWM setting turns
it to the extreme right. The midpoint position corresponds to the PWM value that is halfway between the two end settings.
Figure 20 :: Setting the servo’s limits of motion using the PWM values
For each degree of motion by the servo, the PWM pulse width needs to change by a specific number of us. This “PWM scale” can
usually be found on the data sheet of the servo. Alternatively, you can measure how many degrees the servo moves for a 1000 us
change in PWM pulse width and calculate the PWM scale from this result. The default scale value is 10.00 us per degree as shown in
the picture below:
Figure 21 :: Setting the servo’s PWM scale
Once the settings have been entered, the servo can be manually positioned using the slider near the bottom of the graphic page.
This slider works in 5 degree increments. The central or middle position can be checked by pressing the “Go to midpoint” button.
The midpoint should be lined up with the forward direction of whatever the servo is mounted on. In the graphic, the physical range
of angular motion of the servo is shown as a grey segment.
Note that settings will only be saved to the LW20 once the “Save” button in the bottom left corner of the screen has been pushed.
Once the electrical characteristics of the servo have been entered using the method above, the servo can be used to aim the LW20 in
a specific direction or autonomously scan the LW20 to produce LiDAR maps and provide collision warning alarms.
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Configuring the scanning motion is done by selecting the “Sweep” button under the “Setup” tab. Note that the settings entered here
are limited by the physical and electrical characteristics of the servo. Only the first return signal is shown on the graphic.
Figure 22 :: Setting up the servo’s scanning characteristics
The speed of the scan is determined by how fast the LW20 updates and the number of steps that the servo moves with each reading.
The “Steps per reading” box increases or decreases this speed as does the update rate setting in the “Laser” section. Running the
servo faster increases its power consumption but provides a faster response to changes in measurements. If the servo moves too fast
its range of motion may be decreased.
Each direction of the scan is indicated in a different color on the graphic. This is to emphasize the effect of “servo lag” that most
servos exhibit when moving at a constant speed. Servo lag comes about because servos are designed to aim in a fixed direction and
their control systems are optimized for this type of action. When the servo moves continuously, the control loop isn’t able to catch
up with the aiming direction and always lags behind.
The number of degrees of lag is different for different servos, at different speeds and at different power supply voltages. To correct
for this lag enter a value in the “Lag offset” box. This is typically between 0.5 degrees and 10 degrees depending upon the torque,
speed and quality of the servo. By making small adjustments to the lag offset the images from each direction of scan can be made to
coincide, as seen in the picture below.
Figure 23 :: The effect of servo lag with no correction and after applying a 2.5 degree correction
Once the servo lag has been corrected, the mechanical motion of the servo will remain consistent. From time to time the settings
should be checked in case wear on the gears or changes to the power supply have affected the servo.
In most applications, the field of view of the scanning pattern will need to be reduced. This could be because of fixed objects inside
the scanning area or to remove errors at the edges of the scan caused by the servo changing direction.
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LW20 / SF20 LiDAR sensor
Product manual
Changing the field of view does not affect the physical motion of the servo as this would upset the PWM and servo lag settings.
Instead, the field of view cuts out unwanted data from the edges of the scanned image. The left and right edge settings of the field
of view can be changed independently.
Figure 24 :: Reducing the field of view to avoid detecting the landing legs on a drone
For high precision scanning, the servo can be made to scan in one direction only. The resulting image has higher angular repeatability
at the expense of increased power consumption by the servo when returning to the start of the scan. Switching from bi-directional to
uni-direction scans is done using the “Scan type” selection box.
Figure 25 :: Uni-directional scanning for higher precision
LW20 / SF20 LiDAR - Product manual - Revision 7 | of | © LightWare Optoelectronics (Pty) Ltd, 2018 | www.lightware.co.za20 28