Production Machining

SEP 2018

Production Machining - Your access to the precision machining industrial buyer.

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Voltage mounted directly to the motor, optimizing the space within the machine. is placement also delivers a high mechanical stiffness and allows for a more dynamic range of motion since the forces are not being transferred through multiple parts. Another benefit is the elimination of backlash and inertia mismatch. A force transmission method that can perform over a range of force and speed without having to make mechanical adjustments, and whose performance and precision is only limited by the feedback device to which it is attached, is the result. Despite its benefits, direct-drive technology is not more widely adopted because of the upfront price and complexity of integration. Because of cost of material (mostly the perma- nent magnets) there is often a hesitation toward making the investment to switch over. Additionally, when someone is already familiar with a gearbox or ballscrew solution, its familiarity can be comforting. While those two factors can create some intimidation from the start, what needs to be understood is that a lot of the value from direct drive comes from its long-term use. By maximizing a machine's performance, the manufacturer increases a machine's throughput and reduces the occur- rence of interrupted cycles from machine downtime for maintenance and part failures. When properly integrated, the user has a motor that could be operating 10 years down the line and will perform just as well as one that is newly installed. To get the most out of direct-drive technology, its limitations must also be understood. e concept of the force transmis- sion being coupled directly to the payload can be compared with the concept of semi-closed loop when it comes to encoders. e fewer the degrees of separation between the part, the greater the overall performance will be. Most of the time, a motor's performance is limited by how much force/torque a motor can output without overheating. e continuous value of the motor (continuous force with linear and torque with rotary)—the average value at which a motor can run 24/7—is the most malleable since it depends on how the motor can dissipate heat. If the motor has some type of heat sink or is liquid cooled, performance will increase noticeably, sometimes even doubling with liquid cooling because of how much heat is dissipated. A motor can perform above the continuous value, up to the peak value, but is physically unable to go higher than the peak value, typically because that is the point where so much current is added to the coils that the magnets may be demagnetized. Although not as flexible as the continuous Phase 1 Phase 2 Phase 3 Time 240 120 9 -120 -240 Three-Phase Power :: Torque and linear motors operate on the same principles. :: It's ideal to have current the strongest when a coil is between the magnets. TECH BRIEF 30 PRODUCTION MACHINING :: SEPTEMBER 2018

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