Motion control for 3D laser mapping application: Mclennan size and supply single axis motion system for large scale LiDAR mapping and data acquisition systems
18 September 2018
3D Laser Mapping Ltd is a high technology design, manufacturing and consulting company, based in Nottingham-UK. Its LiDAR scanning hardware and data analysis systems are used for mapping large structures - capturing, processing and providing three dimensional information for surveying tasks such as buildings, road networks and railways as well as creating digital terrain and elevation models of specific landscapes. Amongst a comprehensive range of products and systems targeting these quite diverse areas, 3D Laser Mapping's PROCESSMONITOR LIVE software and 3DLM-SR-50 laser scanner package is aimed at dimensional modelling in particularly harsh environments such as underground construction projects, bridge and structural repairs and sprayed concrete measurement. To ensure the angular positioning precision and optimum reliability required for the laser scanner hardware, 3D Laser Mapping has chosen Mclennan as a supply and support partner for a Modbus over Ethernet-enabled intelligent microstepping drive and planetary gear unit with absolute encoder feedback.
The SR-50 features a LiDAR based scanner and sensing unit that scans in a vertical direction over 160 degrees, whilst its horizontal positioning is handled by the Mclennan single-axis motion solution through 0.25 degree start-stop increments and a full range of 160 degrees. With the Mclennan supplied positioning system housed in an IP65 rated enclosure, along with other instrumentation equipment, this combination interacts with the PROCESSMONITOR LIVE software to provide the acquisition and analysis of real-time imagery that precisely measures the surveyed three dimensional profile.
For example, in a typical application such as concrete spraying (shotcrete) used in tunnel lining and underground mining, the amount of material sprayed may be constantly monitored and optimised by measuring the displacement during the process. This not only guarantees the correct thickness of material which is critical for safety but also ensures that no costly material is wasted. The capability and application scope of this equipment is also widely applied to other hazardous areas. The robustness of the scanner hardware and its component parts is critical - the unit is controlled and data acquired remotely over an Ethernet link and it is normally vehicle mounted on mobile construction machinery with the inherent shock, vibration and temperature extremes associated with the construction and mining industries.
Mclennan were called into the project and began a full sizing and product selection review before making a proposal. This process covered the technical aspects of the application as well the commercial considerations such as field support - as the systems are used globally and back-up is a critical part of 3D Laser Mapping's service to its customers. Cost was also an important consideration for single unit development prototypes as well as for OEM series production.
Mclennan represents a small but select number of major motion control component suppliers, and through its own design and build capability combines such products into complete mechatronic motion-based systems. The main motion components selected were from its Danish and German distribution partners - JVL Industrie Elekronik A/S and Wittenstein alpha GmbH. JVL's MIS34 series 'Quickstep' integrated microstepping motor comprises a programmable stepper motor with a closed-loop capability through an integral absolute encoder and an optional holding brake. The intelligent motor was coupled to a series TP series high torque planetary gear unit from Wittenstein alpha. This combination produced a comfortable margin of torque and precision required to rotate the axis at the relatively moderate speeds that were called for to ensure fast data acquisition throughput.
The use of stepper motor technology was preferred as no tuning would be required as with servomotors - availing a plug and play solution for field replacement and ease of installation. JVL's ServoStep technology however, does provide a closed loop capability with the multi-turn absolute encoder providing an angular resolution well within the required specification. The encoder also provides absolute position which is perfect for setting up the system in the field - no datum routine is required and in the event of power outages, the process can be quickly resumed. The optional power-off activated holding brake was included and was applied to add stability during scanning as well as provide a safety on shutdown to lock the axis for transportation. Furthermore, the 4 arc-min backlash specification for the planetary gear unit ensured excellent repeatability for multiple scans.
JVL's QuickStep series integrated stepper motors are available with a wide selection of NEMA stepper sizes, torque ratings. product variants and control interfaces. These include Profinet, Ethernet/IP, EtherCAT, Powerlink, and many more. For this application Modbus over Ethernet was selected where position commands are streamed into the intelligent controller from a dedicated Wi-Fi link. The controller also has a complement of I/O which is used for the brake and overtravel switches, and was also applied to other timed functions for data collection. JVL's MACTALK allows fast and straightforward set-up and, along with an OXC driver, can be used with any windows based device for positioning and monitoring. The unit operates from a 24 V DC power supply which greatly suits the off-grid nature of the application where battery back-up may be required.
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