The movement profile tips the scales

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Content

November 2016

 

A sophisticated drive design helps to keep the acquisition and operating costs of a machine as low as possible. Just how efficiently and reliably a motor carries out the required motion sequence during operation is determined by the design of the movement profile.

When it comes to designing a drive, distance and time are the main factors. To protect the mechanics, the maximum permissible acceleration and speed values are often specified, as well. The values for time, acceleration and speed may not be exceeded, and the value for the distance may neither be fallen short of nor exceeded. The movement profiles can be calculated on the basis of these specifications, which significantly affect the efficiency of a drive. Software tools provide support. Our example shows what impact the movement profile has on the efficiency and the size of a drive.

The possibilities Magnifier

The possibilities: If both distance and time remain constant, a movement profile can be changed between two extremes: from a triangular move to a trapezoidal move. The acceleration and the effective torque change within these two extremes.


 
 

Selection as per the trapezoidal move

Very strong acceleration forces occur during a trapezoidal acceleration phase with a steeper acceleration ramp.

The effective torque is less than the permissible continuous torque of the motor. The acceleration torque requires such a high maximum torque, that the size of the engine is essentially determined thereof.

Selection as per the trapezoidal move Magnifier
 
The motor is not thermally exploited.

The motor is not thermally exploited.  
Mass: 100%
Installation space: 100%


Selection as per the triangular move

During a triangular acceleration phase, only the slightest acceleration force occurs.

The acceleration torque is much less than the maximum permissible torque of the motor. The RMS torque requires such a high continuous torque, that only the size of the engine is determined thereof.

 
Selection as per the triangular move Magnifier
The motor is not dynamically exploited.

The motor is not dynamically exploited.
Savings versus the trapezoid:
 
Mass: –52%
Installation space: –44%


 

The perfect solution

During a trapezoidal acceleration phase using the 1/3 rule (the acceleration, constant and deceleration phases each last for one third of the entire time), the smallest RMS torque occurs. The maximum torque stands in a balanced relationship. This corresponds to the characteristics of a servo motor.

By using the IndraSize software tool, additional optimization potential can be realized by applying higher order motion laws. That becomes clear when the trapezoidal profile using the 1/3 rule is combined with a third-order polynomial. The RMS torque and the required maximum torque can thus be optimized so that it is possible to select a motor with a smaller design.

The perfect solution Magnifier
 
The motor is optimally exploited.

The motor is optimally exploited.
Savings versus the trapezoid:
 
Mass: –57%
Installation space: –56%


Download the IndraSize engineering tool for free: www.boschrexroth.com/indrasize