LINEAR MOTOR TECHNOLOGY
Linear Motor Axis Drives come standard on Sodick’s EDM equipment and High Speed Mills.
Advantages of linear motor drives:
Eliminates ball screw drives
No backlash or lost motion
Ideal part geometry and finish with reduced skim passes
Fewer wire breaks
Increased cutting speed
No maintenance
10-year Positioning Accuracy Guarantee
What happen to Ball Screws?
The basic technology of ball screws or rotary motor systems had been the standard in EDM up until 1999. At that time ball screws seemed to provide decent accuracy, were able to withstand high thrust loads and incurred minimal friction. However, as time went on, the contact-type ball screws, due to their mechanical design, would wear and have to be replaced.
The time it took for ball screws to wear out would be based on how much the machine was used, but the average was about four to five years, dependent upon the type of application used, load, speed, lubrication, contamination and heat. To maintain the life of the ball screws, thorough cleaning on a regular basis was required. This cleaning would reduce the speed of wear, but not eliminate it. Many shops found it costly and difficult to maintain over the machine's life. A 90 percent reduction in the ball screw's life can be anticipated when operating the nut and screw without lubrication, so proper lubrication was very important.
When a ball screw system is moved at a high feedrate, overshoot and undershoot can occur as a consequence of windup since the load will oscillate around or stop before the desired stopping point, increasing settling time and reducing throughput. This is because the rotary encoder bases positioning on the number of divisions moved by a rotary disk. It does not and cannot take into consideration any thermal conditions; such as, ball screw expansion, twisting in the ball screw due to servo torque, wear or thermal expansion in the ball nut, or coupler and backlash in the ball screw. So the true machine position is compromised.
Sodick wanted to offer their customers a system that would not have problems such as these...that is when linear motors were introduced.
How Linear Motor Drives Work:
Linear drives contain the same components as a servo motor (magnets & copper coils). A linear motor is an uncoiled servo motor. As amperage enters the coils, it creates force that is repelled against the magnets. The motor is also the driving force; thus, eliminating the need for ball screws.
Linear motor technology, which is based on electronic drives, offers an option with several advantages, including improvement in accuracy, repeatability, speed and acceleration. Since linear motors are a direct electronic drive (no mechanical parts), they do not have the backlash and wear problems ball screw drives may have.
Data transmission to linear motors is instantaneous with the use of a motion controller, and over shoot and under shoot does not occur since glass scales are attached to the axis and are used to measure positioning, so the exact position is always known. Linear motors also produce next to no vibration and zero backlash since they are directly driven.
The precision and stability achieved because of no contact makes linear motors an ideal option, even for some applications that do not need their speed but require their accuracy.
Don’t forget – Sodick offers a 10 –Year Positioning Accuracy Guarantee.