Why are the output indexes of the servo motor and the spindle motor different, and the servo motor uses torque (N.m) and the spindle power (kW) as an indicator?
A: Generally speaking, the servo motor and the spindle motor have different functions in the CNC machine. The servo motor drives the table of the head bed. The load damping of the table is the torque that is equivalent to the motor shaft, so the servo motor uses torque (Nm ) as an indicator. The spindle motor drives the spindle of the head bed, and its load must satisfy the power of the machine tool, so the spindle motor is measured by the power (kW). This is the customary name. In fact, through the conversion of the mechanical formula, these two indicators can be mutually calculated.
What is the characteristic curve of the servo motor? What are the typical parameter points on the curve?
Answer: Figure 1 shows one of the main characteristic curves of the servo motor.
On the graph, ωmax is the rated speed and the maximum response speed.
T0 is the continuous rated stall torque, T2 is the continuous rated torque, Tmax is the maximum stall torque, and T1 is the intermittent rated torque. P0 is the rated output power and Pmax is the maximum output power. The stall torque is the minimum measured torque produced by the rotor of the motor when it is blocked at all its corners.
Taking the FANUC servo motor as an example, the above characteristic curve corresponds to a case where the motor current is sinusoidal and the ambient temperature is 20 °C, and has a tolerance of ±10%. If the ambient temperature is higher than it, the working limit has to be lowered. Since the temperature coefficient of the ferromagnetic material is negative, the value on the characteristic curve is lowered. For the case above 20 °C, the value on the curve for each increase of 1 °C is about 0.19% for FANUC and about 0.11% for αis; it is recommended to select 70% of the motor rating as the load full load.
