In a minimum configuration system allows you to estimate the position of the blade when profiling the soil and give the operator a visual signal on its movement in manual mode.  The visual signal is creating by  special device  fixed in the cab and  based on light emitting diodes line (lightbar). Fully equipped system allows not only  to estimate the position, but also to automatically control the blade (through additional electric  control valve installed in machine hydraulic  system) for height and angle with high precision (centimeter and better) . It is  not only  reduces the consumption of building materials by reducing the tolerances, but reduces operator  fatigue  and requirement to his qualification level.  In the case  of a bulldozer automated system will allow you to improve  its profiling performance while provide  greater traction, which in some cases makes possible to completely eliminate of use of moto grader on the construction site at all stages of work except maybe the final.

 If desired, the machine  can be additionally equipped by automatic  steering system. A key component of the system is a subsystem of blade position estimation.

We can offer to your attention two types estimation of blade position: simple two-dimensional (2D) and complete three-dimensional (3D).

Two-dimensional systems

In this case  a profile can be horizontal or inclined plane. Measurement of the position of the blade can be made with a laser receiver receiving a signal from transmitter or ultrasonic rangefinder  measuring distance between blade and metal strings.

Laser transmitter that is installed on the ground is a device generating a laser plane. The plane is created by a mechanical rotation of narrow laser beam (for example, around a vertical axis) in a direction perpendicular to its optical axis. The laser beam can be modulated by a code for protection from interference, but there is not measurement range based on this code. Tilting the device properly, the laser plane can be oriented horizontally or inclined, depending on the desired profile to be cut by machine. There is a mast installed on the blade with a vertical line of photocells receiving the laser beam from the transmitter. The length of the line of about 15 cm. The zero signal (blade is exactly at a desirable profile) corresponds to the case when the beam cross the middle of line. If the beam hits above the middle, one should raise the blade, if it is below – lower. If there are a large differences in initial and final height marks on the site (> 15 cm)  or “piecewise” profile with different heights to avoid necessity to reinstall the transmitter one uses a motorized mast. Built-in motor allows the operator of the machine to raise or lower the line of photocells for getting the beam in the work zone of receiver. To operate the system requires unshaded line of sight between the transmitter and receiver. The length of the line of sight is limited to a few hundred meters. Rain, snow, fog, smoke, dust, leads to a significant decrease in the maximum length of the line at which you can work steadily.

To control the blade slope it is possible to use two receivers mounted on the blade on two masts with some spacing between them. Typical cases – on the left and right edge of the blade or in the middle and at one edge. Instead of the two receivers is also possible to use a tilt sensor which consists of a electronic device that measures the projection of gravitational acceleration on the sensitive axis. Comparing the measurement with a nominal value of acceleration (9.81 m / s ^ 2), the system calculates the angle of inclination. There are tilt sensors based on liquid level sensors and based on MEMS (Micro Electro Mechanical System) accelerometers.

When working with an ultrasonic range finder is required to pull metal strings parallel to the desired profile. Range finder mounted on the blade with help of bracket and measures the distance. Zero signal  usually corresponds to range of about 10 cm. If the distance is less than 10 cm blade should be raised if more lowered. To measure the slope it is possible to use a tilt sensor. This system can be used on graders, but not used on a bulldozer.

Three-dimensional systems

These systems are most effective, versatile and progressive. In this case, the desired profile is a complex surface, usually approximated by triangles on the nodal points given in Cartesian coordinates X, Y, Z. X and Y define the horizontal plane, and Z – height. Measuring three coordinates of the current position of blade can be performed using GNSS (Global Navigation Satellite System) receiver or a laser-robotic total station.

Laser robotic total station is a device based on a laser rangefinder that can measure the distance to the prism installed on the mast of the blade. The prism is an optical device, which returns (reflects) beam in a direction exactly opposite to its arrival. This property is valid for any direction in 360 degree azimuth zone. By measuring delay of the arrival of the reflected beam rangefinder calculates the range.

Rangefinder can deviate in elevation (vertical plane) and azimuth (horizontal plane) with the help of electro – mechanical system. At the beginning the station automatically scans the angular sector which is presumed to contain a prism. When it detects a strong signal reflected from the prism station grabs it and begins to automatically track of its movement continuously forming the current estimates of angles and distances. According to two angles and distance station estimates 3D position of the prism on the blade and transmit it to the control unit on board a machine via a separate radio channel. The slope of the blade is estimated by liquid or MEMS sensor. The control unit compares the desired and the current altitude (Z), as well as the slope using blade azimuth  (orientation in the horizontal plane). Desired height and tilt are determined by the desired profile in the current (X, Y) point. Azimuth defined by the azimuth of the velocity vector in the process of the machine movement. The difference in heights and angles are output as a signal for manual or automatic blade control.

The same requirements of the line of sight between station and prism as for the two-dimensional systems stated over three dimensional optical system. The essential advantage of systems based on the receivers of global navigation satellite systems (GNSS) as opposed to optical are all-weather and lack of requirement for an unshaded line of sight. There is currently deployed two systems: GPS by US and GLONASS by Russia. European GALILEO and Chinese BEIDOU are under development and commissioning. The main principles of such systems is well described in the net. Modern receivers usually support the work of at least two systems, which allows due to signals from a large number of satellites (more than 10) to achieve a good positioning accuracy even in conditions of partial shading of the sky. In order to achieve centimeter accuracy (standard deviation in height of about 10 mm), the receiver operates in differential mode, taking on a separate radio channel the special messages (differential correction) from ground GNSS base station.  In this case the receiver operates in Real Time Kinematic (RTK) mode of positioning. The base station is stationary navigation receiver set on a point with accurately known coordinates and coupled with a transmitter of differential correction. Number of subscribers to a base station, in opposite to laser systems is almost unlimited, i.e. at a construction site there can be simultaneously operated an unlimited number of machine with automatic control and surveyor navigation receiver to monitor profile . The working area is determined by the transmitter  and environment for radio signal  propagation and depending on the power can be more than a few kilometers. The base station can be purchased together with the control system. You can also use a network base station, which can be accessed through the cellular networks (GSM/CDMA/3G). However, this is only possible if the operators of cellular and navigation services presented in your region.

As well as in the case of total station the control system produces signal for manual or automatic blade control based on the calculated RTK position of the blade X, Y, Z, tilt and azimuth. In the case of increased demands for precision 3D profile forming with significant height differences one requires a precise calculation of the azimuth. For this system can be equipped with two receivers GNSS, which antennas are installed on the edges of the blade on the two masts or on a single on a special twist bracket.

If you need to provide millimeter accuracy (standard deviation in height about 3 mm) the system can be additionally equipped with a laser receiver receiving a signal from the laser transmitter operating on a principle similar to the principle of laser 2D systems described above. However, due to special sweep of the laser beam such transmitter can provide an unlimited number of users of the system. However, the working area of the system is limited to a radius of 200 m. To have wider working area one need to reinstall transmitter or use more than one forming an network from them.

If you need to operate a bulldozer at large longitudinal velocity the system can be equipped with an inertial measurement unit (IMU), which measures the acceleration and angular velocity vectors. The processing of these values together with the position of GNSS can significantly improve response of control systems to dynamic impact on the blade. IMU is installed on the blade instead of the tilt sensor and additionally improve accuracy of tilt angle measurement.