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Linear Shaft Motors in Semiconductor Applications

Linear Shaft Motors provide ultra-high precision with high power and modest footprint in the semiconductor market

Linear Shaft Motor servos are somewhat unknown in the machine builder market; they have usually been embedded deep within high-precision OEM systems that handle lithography, wafer scanning, and optical inspection applications. However, in the area of semiconductor automation, they are the motor of choice due to their ultra-precise capabilities. Here are a few of the benefits of using Linear Shaft Motors for semiconductor manufacturing.

NO COGGING: Applications that operate with nanometer precision require a cog-free motor. Cogging occurs with flat linear motors where the iron core of the motor slider (forcer) reacts with the magnets of the magnetic way or track. This pull to the motor’s preferred position (cogging) of the motor causes both force and velocity ripple during motion. This is highly undesirable in applications where absolute smooth ripple-free velocity or force is required by the machine process. The Linear Shaft Motor has no iron core in the forcer, which eliminates potential cogging. This is ideal for applications requiring ultra-smooth motion at any speed.

SIMPLICITY AND RELIABILITY: Mechanical apparatus used in motion control applications can become very complex, such as utilizing multiple pullies and belts, or integration of complex gearing systems. The Linear Shaft Motor, however, can easily simplify a complex mechanical design. The non-contact Linear Shaft Motor solution consists of a magnetized shaft and a set of coils making up the forcer. The machine designer can quickly integrate the shaft motor into the machine using the preferred linear bearing arrangement and desired feedback element to meet performance requirements. Either the shaft or forcer can remain fixed while the other is connected to the load and provides motion. The environmental conditions will also dictate the type of bearing solution that may be required, whether it be industrial or clean room rated.

RESOLUTION: The choice of feedback device allows the designer to select the appropriate resolution and accuracy based on the application requirements. Ultimately, the performance limitation will reside in the control and feedback elements, and not by the capabilities of the shaft motor.

SMOOTH MOTION PROFILES: The Linear Shaft Motor's compact forcer is perfect for small spaces where smooth force control is required. Shaft motors are based on a 3-phase brushless motor design, and as such can be driven by most any brushless servo drive. This provides a wide flexibility in choice based on performance, feature set and communication protocols of a given drive.

HIGH EFFICIENCY: Shaft motors have the highest efficiency of any other linear technology due to their circular magnets – round magnets are stacked end-to-end within a stainless steel tube (shaft), and the forcer coils wrap around the shaft, taking advantage of the full 360 degrees of flux generated by the magnets. There is no other approach that compares. In an independent study, the Linear Shaft Motor proved to be more than 50 percent more efficient than coreless, or U-shaped, linear servos while using about 50 percent less power.

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