mademaster cnc stakles
smart generation

Feed drives


Almost everything depends on feed drives: positioning accuracy, speeds of working motions, accelerations and smooth motions. Nowadays such drives have to meet very high standards.
Professional solutions require applying servo drives, and for less demanding applications, step motors are sufficient.


The main difference between these drives is the position feedback. In the case of step motors all machine movements consist of a large number of single steps generated by the interpolator. Each step, depending on the drive ratio and the amount of microsteps, is from 0005 to 0.1mm. Drives of this type have a very simple structure, which results in a relatively low price. A certain disadvantage is the lack of the measurement of position, and in certain difficult circumstances (overloading) the coordinates may be lost (lost steps), which may cause damage to the processed workpiece or the tool.


Servo drives are devoid of such shortcomings. Their work consists in constant striving to achieve zero deviation, i.e. the difference between the value set and the value measured. The head position is constantly read by the incremental encoders, which can measure the position of the head with the accuracy coming up to 0.001mm. On the basis of this information, the control system controls the motor so that the error was zero. When the load increases, the engine increases the power to prevent arising the deviation of the position, and in the case of exceeding a certain load, the system stops the machine and informs the operator about the need for intervention.


The other difference lies in the overload capacity. A stepper motor has a torque dependent on the current which is flowing through the windings. This current is inflicted by the driver. If the torque is exceeded, the engine "loses steps" and the driver does not know about it. As a result the machine goes further and destroys the material. To prevent such occurence the stepper motor must be loaded with the torque not exceeding 50% of the rated torque at given rotations.


The servo motor works differently. It frequently analyses the position offset, i.e. the difference between the position given and the current position (e.g. from measuring linear scales). The microprocessor in the driver tries to control the torque, that is the motor current, so that the position offset was as small as possible. Due to the fact that the current overload capacity of servo motors reaches a tenfold nominal value, the perceptible power of the machine equipped with servo drives and of the size similar to stepper motors is many times greater.