Brushless DC Servo Motors Power 5-Axis CNC Machine
There is a clear trend towards making components as small and compact as possible, even in mechatronic components. It saves both raw materials and costs; even the production of these components has potential for savings.
A new compact 5-axle CNC (computer numerical control) machine is now making the production of complex small components easier. Despite its small size, the use of brushless micro motors means the system can offer all the properties which were previously the domain of larger systems.
Efficiency is defined as the relationship between costs and benefit. Using large CNC centers for the production of small components is often less than ideal. This is where Wegera Oy from Oulunsalo, Finland comes in. Its compact 5-axis CNC system, Kolibri, represents a practical alternative for small scale production. In order to ensure the necessary precision within small dimensions, the developers have been working together with micro drive experts, FAULHABER in Schönaich near Stuttgart.
Small, But Mighty
Many large machine tools are too big for the production of small components. However, a production system which is adapted to the requirements allows optimum performance at the same time as manageable investment and maintenance costs, with no compromises on product quality. In developing Kolibri, the Finnish machining specialists started with the main requirements and extended their CNC system with modular upgradable options. The result was an application-specific, scaleable machine which is suitable both for stand-alone operation and for integration into a production line. There are two different sizes of Kolibri machine tools. The smaller one is called Kolibri 500 and the larger one is Kolibri 750. Despite its compact proportions - at 500 or 750 x 740 x 910 (W x H x D) it is around one third the size of a standard desk - a real all-rounder. The sealed system design allows environmentally-friendly mist lubrication. The relevant control software can be loaded either via cable or wirelessly via Ethernet. If necessary, the device can be fitted with a remote controller via an Internet connection.
The five-axis machining center can be upgraded to six axes and has a speed-controlled spindle. There are also three and four-axis versions for less exacting requirements. All machines have a machining area of X = 265/470 mm, Y = 420 mm and Z = 160 mm. The A axle can be inclined by +/- 120°. The C axle can be rotated around n x 360°. The machine can be equipped with automatic tool changer with space for 22 tools. If the machine is equipped with the automatic tool changer, it will utilize 1,8 kW/50.000 rpm high speed spindle from Alfred Jäger. The spindle uses HSK-E25 chuck. The established brushless micro motors are used on the fourth and fifth axle, where space is more critical. The patented quick changeable module of fourth and fifth axle includes two servo motors (200W) and motion controllers. A third micro drive with built-in gears is used to move the magazine for changing the tools. All motor functions are controlled using motion controllers, so the actual CNC controller is relieved of the motor functions.
Brushless DC servo motors have a particularly impressive service life and excellent dynamics. For physical reasons, they can be overloaded with values well over the rated performance for brief periods, which also improves acceleration and braking. As the design of micro drives means that they can only achieve their high volume performance at high speeds, the necessary speed is brought up to an application level by means of diameter-compliant gear offsets, where required. This increases both the torque and the resolution on the drive shaft if an encoder is fitted to the motor shaft. Output performance of over 200 W and more than 190 nMN from a motor diameter of just 40 mm are now possible at a speed level of around 16,000 rpm. Where lower levels of performance are required, 35 mm motors may also be used. They can output a good 90 W (50 mNm) at the shaft and can also be adapted to the speed required using gears. The transformation range for robust, lifetime-lubricated planet offset gears with steel gear wheels ranges from 3.71 to 1526:1 or from 4.8 to 2548:1 for 40 mm gears.
The gears are all controlled by means of optimized motion controllers. This means the ideal transformation of the control commands can be achieved for each version of the drive. The 4-quadrant PWM controller works at 95% efficiency and takes the "management" of motor controlling away from the PLC or system controller. At the same time, there is the option of sending independent speed profiles to the motor as well as speed control, positioning mode and various safety functions. Data is loaded through an RS232 interface. The incremental and absolute encoders can also be analysed based on motor type in the same way as Hall sensor signals. There is a comprehensive ASCII command set for simple programming. The FAULHABER Motion Manager makes programming easier by providing a clear graphical interface and represents an easy point of entry into the world of microdrive controls.