Capacitive Linear Encoders for CNC and Laser Cutting & Engraving Applications

Various technologies are available for cutting and engraving materials, such as laser, water jet and plasma. Cutting generally refers to cutting through the material that is being worked in order to either create specific shapes and outlines. Engraving, or etching, refers to removing part of the material, but not cutting right through it. Materials being worked include sheet metal, bulk metals, wood, leather, plastics, and acrylics.

Laser cutting and engraving is a diverse field that ranges from equipment that can be used at home to heavy industrial machinery. The laser device itself must be designed or selected according to the requirements of the application, and appropriate safety measures must always be put in place.

CNC – computerized numerical control – refers to a broad range of automatic machines used for all types of machining. Laser cutting is often used on bulk metal instead of CNC milling since laser cutting does not leave oxide residue on the workpiece and there is no wear to the cutting tool. Of course, every technology has its pros and cons, and the technology should always be carefully chosen to suit the application and to suit cost, environmental, and safety constraints.

Linear Motion in Laser Cutting and Engraving

Linear motion is at the heart of the gantry upon which laser cutting and engraving machines are based. The laser device is mounted on a two-axis gantry, and moved over the surface that is being machined. In some machines, a third axis is used in order to control the height of the laser device, and in even more sophisticated machines a fourth axis, using rotary motion, might be used to control the angle of the laser.

The characteristics of the linear motion that need to be considered when building or selecting a gantry include speed, precision, and stability. There are cost trade-offs to be made in all cases.

• Speed: How fast the laser moves across the work material. This might be a factor in throughput, especially in engraving. Speed affects setup time, too.
• Precision: With what precision the laser is positioned. This determines the accuracy and repeatability of the cutting or engraving.
• Stability: How stable the motion is. Together with precision, this affects the quality of the machining.

The linear motion of the gantry can be achieved using ball screws or linear motors. The choice depends on factors such as cost, speed, precision, stability, as well as on the weight of the laser device. Linear motors, for example, might be more suitable for supporting heavy loads, as well as for increasing the precision.

In high-end machines CNC, linear motion is used for added precision of the work piece. CNC encoders are those that are suitable for use in the typically harsh environment of a CNC machine.

Using Capacitive Linear Encoders in Laser Cutting and Engraving

In laser cutting and engraving systems where linear motors are used, the capacitive linear encoders from KappaSense are a good choice for the motor feedback. The capacitive linear precision encoder can also be used as cost-effective secondary feedback devices in simpler gantries that are based on rotary motors, pulleys and belts. The secondary feedback provides the true position of the laser device, facilitating position precision in such systems. In some applications where there is a high level of electromagnetic interference, the high resolution capacitive linear encoder can be an alternative to expensive fiber optic encoders.

Benefits in laser cutting and engraving systems include:

• Better immunity to dirt, i.e. particles that are created by the cutting and engraving processes, and therefore easier requirements for sealing as compared with optical or magnetic encoders.
• With an accuracy of ±5μm, a resolution of 0.5μm, and repeatability of ±1μm, the FREE^e micro linear encoder platform would easily meet application requirements for many laser cutting systems, and for most, if not all, engraving systems.
• The encoder scale can be made to fit the extent of the linear motion.
• Wide installation tolerance. The KappaSense absolute linear encoders are designed for flexibility in installation, making the process of installing them on the linear motion mechanism that much simpler.