Company Announcement - Electronics and control technologies are becoming increasingly important in construction machinery, which has long been dominated by hydraulic systems. Sensors such as encoders or potentiometers are being used to provide control units with positioning and angular and speed data. This application places high demands on sensors. Outdoor operation is subject to varying climatic conditions such as extreme temperature fluctuations and the ingress of dirt, dust and liquids. The resulting requirements for high ruggedness and a high degree of protection form the basis of Hengstler’s newly designed encoder families, available locally from Countapulse Controls.

Encoders are used for positioning, angular, speed and length measurements in construction machinery applications where they facilitate both the driver’s work and enhance productivity, such as straight-to-the-point positioning of loads for hoisting equipment or restricting work zones in order to protect against collisions. However, they also allow for the introduction of safety-relevant functions, giving warning signals to the driver in case of any emergency. A classic example is the tilting of hoisting equipment such as cranes and excavators due to excessive loads.

Encoders used in construction equipment always prove their capabilities under extremely harsh conditions by providing reliable feedback on the positioning, excursion angles or speeds. The robust encoder families from Hengstler have proven technology that is completely free from sliding contacts and therefore ensures high reliability and longevity. The programmable absolute encoder types in particular do not necessitate any re-adjustment as compared to other technology products.

The proper function and accuracy of potentiometers for example is adversely affected by temperature fluctuations and wear and tear. In addition, encoders offer full 360° scanning, which allows obtaining accurate feedback over a full turn or even several turns. Multi turn versions make it possible to read the exact number of turns at any time, even after voltage drops or complete power failures.

Machinery manufacturers have valid reasons to use reliable sensors, such as legal requirements for the prevention of accidents or registration of vehicles in addition to achieving increased productivity. For example, an overload warning device is required for both crane systems and hydraulic excavators in order to warn the driver as soon as the permissible load is exceeded. For hydraulic excavators, this can be implemented by means of a measuring element that determines the operating pressure in the cantilever (jib) cylinder and which transmits a warning signal to the driver as soon as a defined pressure is exceeded.

This function can be assumed by encoders and supplemented further by providing feedback to the control system. By determining the angle of excursion of each rotating axis of the excavator arm and the slewing ring between the upper and lower trolley, the maximum permissible load in the excavator bucket or crane suspension can be calculated at any time. The appropriate load moment for each position can be entered via the software, thus assisting the driver with warning signals or even active interference with the motor control.

Construction work often has to be carried out in confined areas such as close to electrical overhead power lines or on sites where several hoisting cranes may impede each other or in pedestrian zones. Hoisting equipment such as hydraulic excavators may be used in buildings with restricted ceiling height or mobile cranes in railway loading stations with overhead power lines. In such cases, crane systems use a so-called electronic safety working range.

An electronic control system protects against obstacles by decelerating the crane when it comes too close to an obstacle and thus preventing a collision. Anti-collision systems are also used for large construction sites with several cranes. They monitor each crane position and reliably prevent them from getting too close to the neighbouring crane. In this regard, encoders determine the exact position and excursion angle of the machine and transmit it to the control electronics.

The work of crane operators is made so much easier if loads are positioned straight to the point. To achieve this, an encoder continuously provides feedback to the control unit on the position and speed of the crane. Set points can thus be selected by means of micro fine turning adjustments and compensating for the effects caused by the prevalent wind or load conditions by means of the appropriate counter movements.

Hydraulic wheel excavators are generally only approved for road traffic conditions if equipped with a sensor ensuring that the upper trolley is aligned in the driving direction. Inductive sensors are often used for this purpose. However, installing an encoder in the rim between the upper and lower trolley has opened up new possibilities. The essential technical requirements for using encoders in construction equipment include a high degree of protection, wide temperature range, high shock and vibration resistance, high resistance to water and humidity, as well as high load resistance of the shaft. Encoders should have a protection rating of IP67 or even IP69.

A temperature range from -40°C to 100°C ensures perfect operation under harsh environmental conditions such as direct exposure to sunlight and fluctuating temperatures. To prevent water condensate caused by internal heating and cooling phases, the enclosure should be specifically sealed. The shock resistance varies depending on the application. Since construction equipment is often cleaned by means of steam jet cleaners, high resistance to compressed water is also of great importance.

Hengstler’s heavy duty product family offers suitable encoders for all such requirements. Extremely high mechanical ruggedness for example is achieved by using a state of the art opto-ASIC and coding disk made of plastic instead of the common glass type, which may break under extreme load conditions. This product series is also available with stainless steel enclosure according to NEMA 4x and 6P with double sealing, ensuring reliable operation in environments that require high resistance to high pressure steam cleaners or corrosive chemicals.

Hengstler offers another extremely rugged product family with special features such as a particularly rugged enclosure and generously dimensioned self contained ball bearings, thus making it resistant to high mechanical stresses and even high axial and radial forces. A 12-bit resolution allows highest acceleration rates and underwater operation. All products are electrically compatible with standard encoders and available with common interface types such as SSI, BiSS, CANopen, analogue or parallel.

Rugged technologies make it easier for electronic components to enter and become established in the field of construction equipment. They also respond to the requirements for high safety, productivity and operator convenience. Even if it might take another few years for electronics to replace hydraulics, it is already obvious that the role of sensor technology will become increasingly important.

ENCODERS IN CONSTRUCTION MACHINERY 01: Technology and flexibility are the key characteristics of the Hengstler Acuro series range of incremental and absolute rotary encoders available from Countapulse Controls.