Ballscrews for long machine travel application can be expensive and can require additional motion components for sufficient support over the needed travel distance. If a machine application requires high operating speeds as well, then machine costs can increase because of the need for larger servomotors and servo drives. The design engineers at Proteck, an Indian production machinery supplier, were designing a machine to meet these specifications. In addition, the machine needed to maintain ±10 micron bi-directional repeatability to 110 m/min linear speed. The engineers turned to Kollmorgen EU to help them reduce the machine’s costs and power requirements, while maintaining or increasing operating efficiency.
The company began with high specification CO2 equipped 3-axis laser cutting machines with flying optics that cater to a range of flat sheet material. These small footprint machines included cast-iron beds and single lower axis geometry that allowed open three-side access for flat sheet sizes around 2.5 x 1.5 m. Based off this machine, the company introduced a model that included all of the features of the previous machines, but used a lighter, lower cost welded frame construction.
The result was the introduction of a rack and pinion drive system for the long-travel lower axis of the machine for a 3-axis bridge laser machining center, which consists of two synchronized lower X-axes supporting a gantry Y-axis, and a vertical Z-axis.
The initial concept looked at linear motor technology for the long-travel dual synchronized X axis, but the cost was prohibitive for the target market. Engineers designed the rack and pinion system knowing that backlash and repeatability performance would need to be achieved using a different method. A special preload mechanism was created by mounting the pinion and its motor on an eccentric pilot circle and a gear tooth geometry that allowed full-face gear contact and in-situ adjustment to minimize lost motion and hysteresis. This performed well at the rack and pinion face, but when combined with a standard rotary servomotor, which required a planetary gearbox to develop the torque required to drive the load, the small gearbox backlash proved prohibitive. The answer was to design the pinion-to-rack transmission around the Kollmorgen KBM series direct drive motor.
The KBM’s separate rotor and stator packages come in kit form and are directly mounted on the machine within its own bearing system and protective cover, with power and encoder connectors built-in. The mounting arrangement directly couples the large diameter pinion shaft to the rotor as a single, solid assembly, restricting lost motion and potential unwanted harmonics. The resulting design was field proven for low backlash and has a dynamic and throughput specification. The rack and pinion system is resistant to debris and does not require the degree of protection that a linear motor system would need in a laser-machining environment.
The company has made use of KBM and AKM motors in other systems as well. The Proteck rack and pinion system, combined with the Kollmorgen direct-drive KBM motor, has fewer parts, is energy efficient and delivers high speed and accuracy, reducing backlash and lost motion to below the desired specification. Kollmorgen S700 servo drives, with multi-feedback capability, are used with both resolver feedback, mounted on the KBM motor for commutation, and magnetic linear scales for the position loop.
The feedback protocol is SSI absolute, EnDAT or BiSS to suit a choice of CNC controllers with set-up and monitoring through EtherCAT, which is integrated in all S700 drives. These include STO (Safe Torque Off) for SIL 2 and 3 safety standards and Ethernet connectivity for set-up and monitoring.
With a maximum sheet size of 3.1 x 1.6 m, the flat sheet cutting machines also use Kollmorgen AKM series rotary servomotors with Micron series planetary gear heads for the Y-axis as well as the Z-axis with a brake fitted.
Building off the flat-bed, 3-axis bridge gantry machines, the company’s laser cutting machine, the Sl 2530, is a 7-axis machining center, which includes a flying optics head design that allows laser cutting of vertical and angled sides of formed workpieces. Large 3D-fabricated sheet metal workpieces are fixed to a stationary central table and the multi-rotational laser head is guided to maintain the optimum perpendicular angle for perfect cutting.
KBM direct-drive motors with Proteck’s rack and pinion mechanism are used for main horizontal axes of the machine, which cover an area of 1.6 x 3.3 x 0.7 m. Furthermore, the hollow shaft KBM motor is used as the main drive for the multi-rotational flying optics system, allowing feed-through of the laser delivery and focusing system while maintaining the flexibility and precision to provide synchronized twin rotary axes featuring nX360° and +/- 135° rotational strokes. The machine also uses a complement of AKM servo motors on other axes along with matching S700 drives, allowing the reduction of spares and inventory costs.