Spindle control system and numerical control apparatus

A numerical control apparatus, including a CNC bus and a spindle, for controlling a spindle motor and a servomotor, comprising:

• a servo control circuit, coupled to the CNC bus, for providing a command, said servo control circuit including:
• a microprocessor for processing a numerical control program;
• a memory coupled to said microprocessor;
• and
• first and second counters, coupled to said microprocessor, for counting pulses, said second counter coupled to the spindle motor to count the pulses produced by the spindle motor;
• a power amplifier, coupled to said servo control circuit, for receiving the command from said servo control circuit and for controlling the rotation of the spindle motor;
• and
• a separate encoder, coupled to said first counter and the spindle, for feeding back pulses to said first counter for contouring control, said servo control circuit being adapted to drive the servomotor through said power amplifier by changing only the numerical control program.