Industrial Servo Motor Yaskawa AC Sigma II Servo Motor 30W 100V 6mm SGMAH-A3BAF21

 

 

 

 

 

 

 

 

 

Let's discuss why one might want to introduce an Integral factor into the gain (A) of the control. The Bode diagram shows A approaching infinity as the frequency approaches zero. Theoretically, it does go to infinity at DC because if one put a small error into an open loop drive/motor combination to cause it to move, it would continue to move forever (the position would get larger and larger). This is why a motor is classified as an integrator itself - it integrates the small position error. If one closes the loop, this has the effect of driving the error to zero since any error will eventually cause motion in the proper direction to bring F into coincidence with C. The system will only come to rest when the error is precisely zero! The theory sounds great, but in actual practice the error does not go to zero. In order to cause the motor to move, the error is amplified and generates a torque in the motor. When friction is present, that torque must be large enough to overcome that friction. The motor stops acting as an integrator at the point where the error is just below the point required to induce sufficient torque to break friction. The system will sit there with that error and torque, but will not move.

 

 

 

The excitation sequences for the above drive modes are summarized in Table 1.
In Microstepping Drive the currents in the windings are continuously varying to be able to break up one full step into many smaller discrete steps. More information on microstepping can be
found in the microstepping chapter. Torque vs, Angle Characteristics

The torque vs angle characteristics of a stepper motor are the relationship between the displacement of the rotor and the torque which applied to the  rotor shaft when the stepper motor is energized at its rated voltage. An ideal stepper motor has a sinusoidal torque vs displacement characteristic as shown in figure 8.

Positions A and C represent stable equilibrium points when no external force or load is applied to the rotor
shaft. When you apply an external force Ta to the motor shaft you in essence create an angular displacement, Θa

. This angular displacement, Θa , is referred to as a lead or lag angle depending on wether the motor is actively accelerating or decelerating. When the rotor stops with an applied load it will come to rest at the position defined by this displacement angle. The motor develops a torque, Ta , in opposition to the applied external force in order to balance the load. As the load is increased the displacement angle also increases until it reaches the maximum holding torque, Th, of the motor. Once Th is exceeded the motor enters an unstable region. In this region a torque is the opposite direction is created and the rotor jumps over the unstable point to the next stable point.

 

 

When the feedback (F) does not match the command (C), an error (E) is computed (C - F = E) and
amplified to cause the motor to run until C = F and E = 0. The equations are simple and help provide
insight into the servo:
EA=F or E=F/A
and C - F = E OR C - F = F/A (substitution)
thus CA - FA = F
CA = F + FA
CA = F (1 +A)
CA/(1 + A) = F
The feedback (which is also the output) reproduces the command by the ratio of A/(1 + A). If A is
large, this ratio becomes 1 and if small, it becomes A. Since a motor is an integrator, if it is driven
with a constant error, it will run forever, so F (in position terms) will increase indefinitely - this
means that the value of A is infinite (not really) for a DC error. If E is a sine wave, the value of A
will vary with the frequency of that wave. When the frequency doubles, A drops in half. If one plots
the ratio of A/(1 + A) with frequency, one gets a curve similar to a simple R-C filter.