Lightware LW20 User manual

LW20 / SF20
LiDAR sensor
Product manual
Table of contents
LW20 / SF20 LiDAR - Product manual - Revision 2 | of | © LightWare Optoelectronics (Pty) Ltd, 2017 | www.lightware.co.za1 25
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.
eters to sense remote objects

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 :: I2C and power cable 21........................................................................................................................
Product ordering codes
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.
Product ordering codes 2.....................................................................................................................................
1. Overview of the LW20 3...................................................................................................................................
2. What can the LW20 do? 3.................................................................................................................................
3. What are the main characteristics of the LW20? 4...................................................................................................
4. Specifications of the LW20 / SF20 5....................................................................................................................
5. How to communicate with the LW20 using the graphical interface 6.............................................................................
6. How to communicate with the LW20 using a terminal emulator 9.................................................................................
7. How to communicate with the LW20 using a controller 13..........................................................................................
8. How to do an initial setup of the LW20 14.............................................................................................................
9. How to set up a scanning LiDAR using a digital servo 15............................................................................................
10. How to set up the alarms 19.............................................................................................................................
11.
Limitations 19
..............................................................................................................................................
12. Instructions for safe use 20..............................................................................................................................
Appendix A :: Dimension drawings 20.......................................................................................................................
Appendix B :: Cables 21.......................................................................................................................................
Appendix C :: Complete command set for machine-to-machine communications 22................................................................
Revision history 25..............................................................................................................................................
Model family Model name Model description
LW20 LW20/SER (100 m) LiDAR sensor with serial output, max 100 m
LW20 LW20/I2C (100 m) LiDAR sensor with I2C output, max 100 m
SF20 SF20 (100 m) Open frame LiDAR sensor with serial and I2C output, max 100 m
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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 5V 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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LW20 / SF20
LiDAR sensor
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 m 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 m with a resolution of 1 cm. The accuracy of
each measurement is ±10 cm.
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.
SF20 LW20
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LW20 / SF20
LiDAR sensor
Product manual
4. Specifications of the LW20 / SF20
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.
LW20/*** (100 m) SF20 (100 m)
Weight 20 g (excluding cables) 10 g (excluding cables)
Range 0 … 100 m
Resolution 1 cm
Update rate 48 … 388 readings per second
Accuracy ±10 cm
Outputs & interfaces LW20/SER: 3.3 V and LW20/I2C: 3.3 V Serial and I2C: 3.3 V
Power supply voltage 4.5 V … 5.5 V
Power supply current 110 mA
Laser power <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 32.1 mm
Operating temperature -30 .. +50°C
Approvals FDA: 1710193-000 (2017/02) FDA: 1710193-000 (2017/02)
Housing Aluminium, ABS plastic and glass ABS plastic and glass
Optical aperture 28 mm x 15 mm
Beam divergence 0.2°
Lens material Glass
Connections Wire tail, 5 core plus shield
Enclosure rating IP 67 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 (Rev 1.2 or higher)
•Open the Terminal application
•Select the “Laser” icon
•Set the baud rate to 921600
•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
TTL-232R-3V3-WELW20/SER
shield
to servo
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LW20 / SF20
LiDAR sensor
Product manual
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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LW20 / SF20
LiDAR sensor
Product manual
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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LW20 / SF20
LiDAR sensor
Product manual
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 921600
•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 “enter”. 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.
TTL-232R-3V3-WELW20/SER
shield
to servo
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LW20 / SF20
LiDAR sensor
Product manual
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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