Heidenhain: Incremental Sealed Linear Encoders (LF 185 Series)

Incremental linear encoders with full-size scale housing

Linear encoders from HEIDENHAIN for numerically controlled machine tools can be used nearly everywhere. They are ideal for machines and other equipment whose feed axes are in a servo loop, such as milling machines, machining centers, boring machines, lathes and grinding machines. The beneficial dynamic behavior of the linear encoders, their high permissible traversing speed, and their acceleration in the direction of measurement predestine them for use on highly-dynamic conventional axes as well as on direct drives.

HEIDENHAIN also supplies linear encoders for other applications, such as:

Advantages of Linear Encoders

Linear encoders measure the position of linear axes without additional mechanical transfer elements. The control loop for position control with a linear encoder also includes the entire feed mechanics. Transfer errors from the mechanics can be detected by the linear encoder on the slide, and corrected by the control electronics. This makes it possible to eliminate a number of potential error sources:

Therefore, linear encoders are indispensable for machine tools on which high positioning accuracy and a high machining rate are essential.

Mechanical Design

The linear encoders for numerically controlled machine tools are sealed encoders: An aluminum housing protects the scale, scanning carriage and its guideway from chips, dust, and fluids. Downward-oriented elastic lips seal the housing.

The scanning carriage travels along the scale on a low-friction guide. A coupling connects the scanning carriage with the mounting block and compensates the misalignment between the scale and the machine guideways.

Depending on the encoder model, lateral and axial offsets of ±0.2 mm to ±0.3 mm between the scale and mounting block are permissible.

Thermal Characteristics

The combination of increasingly rapid machining processes with completely enclosed machines leads to ever-increasing temperatures within the machine’s work envelope. Therefore, the thermal behavior of the linear encoders used becomes increasingly important, since it is an essential criterion for the working accuracy of the machine.

As a general rule, the thermal behavior of the linear encoder should match that of the workpiece or measured object. If the temperature changes, the linear encoder must expand or contract in a defined, reproducible manner. Linear encoders from HEIDENHAIN are designed for this.

The graduation carriers of HEIDENHAIN linear encoders have defined coefficients of thermal expansion (see Specifications). This makes it possible to select the linear encoder whose thermal behavior is best suited to the application.

Dynamic Behavior

The constant increases in efficiency and performance of machine tools necessitate ever-higher feed rates and accelerations, while at the same time the high level of machining accuracy must be maintained. In order to transfer rapid and yet exact feed motions, very high demands are placed on rigid machine design as well as on the linear encoders used.

Linear encoders from HEIDENHAIN are characterized by their high rigidity in the measuring direction. This is a very important prerequisite for high-quality path accuracies on a machine tool. In addition, the low mass of moving components contributes to their excellent dynamic behavior.

Availability

The feed axes of machine tools travel quite large distances—a typical value is 10 000 km in three years. Therefore, robust encoders with good long-term stability are especially important: They ensure the constant availability of the machine.

Due to the details of their design, linear encoders from HEIDENHAIN function properly even after years of operation. The contact-free principle of photoelectrically scanning the measuring standard, as well as the ball-bearing guidance of the scanning carriage in the scale housing ensure a long lifetime. This encapsulation, the special scanning principles and, if needed, the introduction of compressed air, make the linear encoders very resistant to contamination. The complete shielding design ensures a high degree of electrical noise immunity.

Sealed Linear Encoders

Sealed linear encoders from HEIDENHAIN are protected from dust, chips and splash fluids and are ideal for operation on machine tools.

Sealed linear encoders are available with:

Full-size Scale Housing

Slimline Scale Housing

The aluminum housing of a HEIDENHAIN sealed linear encoder protects the scale, scanning carriage, and its guideway from chips, dust, and fluids. Downward-oriented elastic lips seal the housing. The scanning carriage travels along the scale on a low friction guide. It is connected to the external mounting block by a coupling that compensates unavoidable misalignment between the scale and the machine guideways.