What is machine control?
Machine control involves the integration of positioning tools into construction machinery. Various hardware and software solutions exist with the sole purpose of determining a machine's current position on the earth and then comparing that position with a desired design surface. The difference is then displayed inside the machine cab allowing the operator to easily and efficiently determine what is required to create the intended design on the ground.
Machine control, guidance, automation – what’s the difference?
Machine control, machine guidance and machine automation are generally used fairly interchangeably within the construction and mining industries.
Technically speaking 'machine control' is the generic term used to describe the technology as a whole. The term 'machine guidance' refers to indicative systems – those systems that purely display the design difference to the operator. The term 'machine automation' refers to those systems that not only show the operator the design difference but are also able to directly control the machine hydraulics to maintain a desired position. Fully automatic machine control systems are typically used for final grading to gain precision levels.
The use of the term 'machine guidance' for this website is a bit of a play on words. We hope to provide guidance and supporting information for all machine control products and processes.
How was machine control conceived?
Machine control technologies are essentially an extension of traditional survey tools. Over time, inventions have appeared that have made a surveyor's job not only easier but much more accurate. Today surveyors can utilise GPS satellite technology to determine centimetre accurate positions along with EDM Total Station measurement tools for millimeter accuracy. Survey software has become more user-friendly and intuitive allowing for efficient and widespread field use, including the integration into construction machines.
Basic machine control devices were developed in the 1970's with the invent of the Global Positioning System or GPS. However, it wasn't until the late 1990's when GPS reached its maturity that machine control really started to be utilised on construction machinery. Dramatic technological improvements over recent years along with more cost-accessible technology and greater industry awareness have all helped develop the concept of machine guided construction.
The Australian construction and mining industries are at the forefront of utilising machine control technology as a compliment or replacement for traditional survey methods. That being said, the market penetration of machine control products could be estimated at 10-15%. Machine control will almost certainly continue to be integrated into the construction and mining industries and the opportunities for practical uses within other industries are yet to be discovered.
What is GPS?
GPS (Global Positioning System) is a worldwide satellite-based positioning system. Each satellite is able to send a radio signal back to earth that can be received and processed to determine a relatively accurate position. GPS receivers require an unobstructed sight to at least 4 of the 24 functioning GPS satellites at any one time in order to determine a position on the ground.
The GPS network was created and is maintained by the United States Department of Defence. Initially developed as a military tool, the satellite codes have been released to the general public, making GPS positioning data freely accessible to anyone with a GPS receiver.
Technically speaking, GPS refers to the original USA satellite system. The Russian GLONASS system also provides satellite navigation systems. Modern receivers are able to receive both constellations which collectively are referred to as the Global Navigation Satellite System - GNSS.
How does GPS work?
Using GPS satellite positioning techniques is all about measuring distances. Distance is a product of rate and time. Satellite signals travel at the speed of light and the time taken to get to the receiver is measured using extremely accurate atomic clocks. GPS receivers can determine a position range based on the measurements from a single satellite signal. By intersecting the position range (called trialateration) from at least 4 satellite signals, a receiver can calculate its known position within an expected error. The more satellite ranges a receiver can process, the less error in its position.
Unfortunately, there are additional causes of error when dealing with satellite signals. Refraction (or bending) of the satellite signals is caused when travelling through the earth’s atmosphere and can also occur when close to some metallic objects (called multi-pathing). Using satellite signals alone will result in a 10-20 meter accuracy. This amount of error is OK for your average car or boat navigation system but is not adequate for construction machinery systems.
Luckily, the errors caused by refraction can be adjusted with the use of a GPS base station. A base station is a separate GPS receiver that is located within or close to a construction site, mounted over a point with known coordinates. The base station receives the same satellite errors as all other receivers, but because it knows its true position it is able to calculate the satellite signal error and therefore determine what is required to correct the satellite position data. The base station then transmits these corrections to all other GPS devices in range (including machine control and surveyor units). This process is called Real Time Kinematics (RTK) and utilising it allows for a GPS accuracy of 10-30mm!
How does GPS machine control work?
GPS machine control systems use a combination of satellite antenna(s), satellite signal receiver(s), on-machine sensor(s), base station radio receiver and cab-mounted display(s) when utilising GPS satellite guidance. The GPS antenna receives the satellite signals which are decoded by the receiver. When using RTK machine control, the on-board radio also receives the corrections that are being transmitted from the base station. The machine control system processes all this data constantly to produce the real-time position of the machine’s GPS antenna.
The GPS antenna is mounted directly on to the outside of the machine so as to maintain a clear line of sight to the sky. The calculated position of the antenna is transferred throughout the machine by a combination of sensor readouts and complex mathematical equations so as to determine the exact position of the machines ground-breaking attachments. For example, a grader may have one GPS antenna mounted above one side of the blade. In order to determine the position of the other side of the blade, dimensional measurements are combined with sensor readouts such as the rotation, slope and pitch of the grader blade. Excavators use two GPS antennas mounted at the rear of the machine which can quickly determine the machine’s body position. This is then combined with sensor readouts along the stick and boom to determine the bucket’s current position.
The user interface or GPS display is mounted inside the machine cab. The display receives and processes all the information from both the GPS receivers and the sensors to calculate the machines current position. The display also contains the design information and can compare the current and desired positions to calculate a horizontal and vertical difference. The display processes all of this information at break-neck speeds to display the real-time cut/fill on its screen.
Can I only use GPS for machine control?
When most people think of machine control they think of GPS guidance, but it is by no means the only way! GPS and machine control work well together on large bulk earthworks operations and help achieve vertical results accurate to +/- 30mm. Other popular positioning methods are via laser and total station guidance.
Laser transmitters emit a 360 degree beam of light on either a level plane, single slope or dual slope. This beam can be read by the machine control system to calculate an elevation accurate to +/- 10-15mm. Laser systems can also be augmented with GPS position data thus enabling a GPS horizontal position with the more accurate laser elevation.
Total station positioning works in much the same way as GPS positioning with a lot more accuracy. The position of the total station instrument is determined by a resection of at least 2 known points in the same way as you would see a surveyor work. After the instrument has been located it can be set-up to robotically measure a machine-mounted target. The instrument measures distances and angles and then transfers the positioning data to the machine control display to be processed in real-time. Total station positioning is the most accurate positioning solution currently available achieving results of +/-5mm. Total station positioning is usually reserved for final pavement operations.
Why use machine control?
There are numerous advantages to utilising machine control technologies. Users are realising productivity gains of up to 100% (twice as fast!). Less reliance for on-the-ground setout and grade checking is resulting in reduced survey and earthworks personnel costs. Eliminating guesswork is resulting in increased accuracy and re-works as well as material savings. Machine control provides operators and surveyors alike with more job satisfaction which helps increase employee retention. Most importantly, the reduction of on-the-ground workers means massive advancement in workplace safety.
How much does it cost?
Costs for machine control system vary significantly depending on the system requirements and desired accuracies. Suffice it to say that any machine control system is a significant outlay. However, with such huge operational advantages and potential operational cost savings, it does not take long for a project that is utilising machine guidance effectively to realise the massive costs benefits, especially when comparing machine guided construction to traditional construction methods.
What type of machine can I use it on?
Where there’s a will, there’s a way! Machine control systems are being used on most typical construction machinery and can be customised to fit just about any earthworks operation available. Typical machine applications include graders, excavators, bulldozers, compactors, scrappers, pavers and tunnel-boring machines. Machine control can also be commonly found on trimmers, smooth-drum rollers, backhoes, kerb and channel machines … the list goes on!