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6.8 Servo axis - tuning for velocity control

Drive amplifiers designed for velocity control incorporate their own velocity feedback term to provide system damping. For this reason, KDERIV (and KVEL) can often be set to zero.

Correct setting of the velocity feed forward gain KVELFF is important to get the optimum response from the system. The velocity feed forward term takes the instantaneous velocity demand from the profile generator and adds this to the output block (see Figure 45). KVELFF is outside the closed loop and therefore does not have an effect on system stability. This means that the term can be increased to maximum without causing the motor to oscillate, provided that other terms are setup correctly.

When setup correctly, KVELFF will cause the motor to move at the speed demanded by the profile generator. This is true without the other terms in the closed loop doing anything except compensating for small errors in the position of the motor. This gives faster response to changes in demand speed, with reduced following error.

Before proceeding, confirm that the encoder feedback signals from the motor or drive amplifier have been connected, and that a positive demand causes a positive feedback signal.

6.8.1 Calculating KVELFF

To calculate the correct value for KVELFF, you will need to know:

HThe speed, in revolutions per minute, produced by the motor when a maximum demand (+10V) is applied to the drive amplifier.

HThe setting for LOOPTIME. The factory preset setting is 1ms.

HThe resolution of the encoder input.

The servo loop formula uses speed values expressed in quadrature counts per servo loop. To calculate this figure:

1.First, divide the speed of the motor, in revolutions per minute, by 60 to give the number of revolutions per second. For example, if the motor speed is 3000rpm when a maximum demand (+10V) is applied to the drive amplifier:

Revolutions per second

=

3000 / 60

=50

2.Next, calculate how many revolutions will occur during one servo loop. The factory preset servo loop time is 1ms (0.001 seconds), so:

Revolutions per servo loop

=

50 x 0.001 seconds

=0.05

3.Now calculate how many quadrature encoder counts there are per revolution. The NextMove ES counts both edges of both pulse trains (CHA and CHB) coming from the encoder, so for every encoder line there are 4 ‘quadrature counts’. With a 1000 line encoder:

Quadrature counts per revolution

=

1000 x 4

 

=

4000

4. Finally, calculate how many quadrature counts there are per servo loop:

Quadrature counts per servo loop

=

4000 x 0.05

 

=

200

6-22 Operation

MN1928

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Baldor MN1928 installation manual Servo axis tuning for velocity control, Calculating Kvelff

MN1928 specifications

The Baldor MN1928 is a highly regarded motor designed for a variety of industrial applications, known for its durability and efficiency. This motor is part of Baldor’s extensive range of products, which are engineered to meet the demands of heavy-duty operations.

One of the key features of the Baldor MN1928 is its robust construction. Built with high-quality materials, this motor is designed to withstand harsh environmental conditions often found in industrial settings. The steel frame is not only resilient, but it also enhances the motor's cooling capabilities, enabling it to perform effectively over extended periods.

The MN1928 is equipped with advanced technologies that optimize its performance. One notable technology is the use of high-efficiency induction motor design. This reduces energy consumption significantly and contributes to lower operational costs. The motor is also designed with a continuous duty rating, making it capable of running for long hours without compromising its functionality or lifespan.

In terms of characteristics, the Baldor MN1928 features a reliable ball bearing design, which minimizes friction and wear, ensuring smoother operation and increased reliability. With a horsepower rating that suits a range of applications, it provides the necessary torque and speed to power various machinery effectively. The multi-voltage design allows for versatile installation options, accommodating different electrical systems while ensuring efficient performance.

Another important characteristic of this motor is its ease of maintenance. The design allows for straightforward access to components, making it simple for technicians to perform routine checks and maintenance. This is particularly beneficial in industrial settings where downtime can be costly.

Safety is also a priority in the design of the Baldor MN1928. Equipped with thermal overload protection, it prevents overheating, reducing the risk of damage caused by excessive temperatures during operation. Additionally, the motor complies with various industry standards, ensuring safe operation within diverse environments.

In summary, the Baldor MN1928 stands out as a reliable choice for industrial applications, offering a combination of durability, efficiency, and advanced technology. Its robust construction, high-efficiency design, and safety features make it a preferred option for many enterprises seeking dependable motor solutions.