Design News, January 2013

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axes place stringent requirements on the accuracy of the feed be detected by the drive controller. One revolution of the drive drives. Depending on the type of position measurement, the motor with eccentric pinion causes motion errors of the tilting errors of the additionally required rotary and tilting axes can axis in the range of ±10 angular seconds. The error repeats itself cause significant limitations on workpiece quality. It is therefore every 3 degrees with respect to the tilting angle. essential to pay special attention to the correct encoder and its integration into the control loop. RequiRements FoR the AccuRAcy The periphery of the polygonal workpiece is machined in one oF RotARy Axes revolution of the C axis with simultaneously interpolated move- The sides of prismatic components are often machined in ment of the B axis. During machining of the lateral surface, the opposite orientations. In this case, one side is machined first B axis is tilted in and out five times in a tilting range between — perhaps by using a tilting axis to incline the workpiece 1 degree and 19 degrees. with respect to the tool. The workpiece is Five-Axis To examine the effect of position measurethen turned 180 degrees by a rotary table to ment on the result of machining, workpieces machine the opposite side. mAchining were machined with the B axis separately in Machining in opposite orientations places pRovides a closed loop and in a semi-closed loop. All stringent demands on the positioning accuother axes were in a permanent closed loop. racy of the rotary table. Even small angular consideRAble In a semi-closed loop, mechanical errors potentiAl FoR errors in the turnabout movement result in of rotary axes can cause position errors and errors in the parallelism of opposite sides Reducing therefore result in inaccuracy. Tilting axes of the workpiece. On a workpiece with a often have drives with multiple-stage gearing. 500mm edge length clamped at the center of mAchining For uniform motion in a tilting axis, all gear a rotary table, a positioning error of only two times. components must have high manufacturing millidegrees results in an error of 0.01mm accuracy and be assembled precisely. Even perpendicular to the surface. Positioning small eccentricity errors of the gear can cause distinct fluctua- errors can occur on rotary axes when the machining position tions in the speed of the tilting axis. is measured at the shaft of the drive motor (semi-closed loop), If the tilting axis is controlled in a semi-closed loop, the because the errors in the rotary axis transmission (play, elasticsinusoidal position error generated by the transmission cannot ity, radial runout of the gear shaft) cannot be included in the OEM GAS AND LIQUID PUMP SOLUTIONS Smart OEM designers partner with KNF for their custom-engineered diaphragm pumps Flexible Shaft Couplings Electroformed Bellows Technology Ideal for: OR Basic DC Pump Custom-Engineered OEM Brushless DC Pump We prefer to partner with you, engineer to engineer, to understand your instrument's key design parameters and performance requirements. This collaborative approach responds fully to your special needs-meeting your specs and exceeding your expectations. • • • • • • • • • Electrical connectors Motor speed controls Logic control interface Locking baseplates Special tubing Silencers Separation lters Coated metal heads Shock mounts/isolators [ w w w. de s ig n n e w s . c o m ] • • • • • • And feature: • • • • • 609-890-8600 KNFUSA.COM Robotics Encoders Resolvers Servomotors Computers Tachometers Low elastic wind-up Zero backlash Precision control Minimal side loading More...! Visit our website to learn more! Order a FREE Sample! "Building Success Stories One at a Time" J an uary 2013 f luid p o we r / mo t io n co nt r o l / a s up p le me nt to de s ign news F9

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