The goal of all mechatronics, or motion control applications, is to do work. Sometimes the nature of the work is complex and the mathematical description of it can involve some exotic math, but at the end of the day, it’s about force exerted over time. Regardless of how simple or complex, it’s all about the work being done, which makes mechatronics a field whose boundary is entirely mechanical. After decades of discussion, the fact is that motion control, or mechatronics, continues to be confusing to almost everyone, even some of the so-called experts in the field.
For those of you who may not have mechanical engineering in your background, hopefully you may have seen the definition of the horsepower. The work done is 75kg lifted 1 meter in one second.
In English units, it was originally 550 pounds 1 foot in one second. English units are probably more appropriate since James Watt who coined the term was English, but no matter.
Consider the definition of the horsepower in the context of today’s engineering. In order to implement lifting Three types of engineering are required to implement this project as a motion control project. Electrical engineering is needed to analyze how much electrical energy can be supplied to perform the task and determine the best way to protect the circuit from dangerous conditions. Control engineering is required to select and program a control system to perform the work. Mechanical engineering is required to size a pulley, rope and harness to safely attach the horse to the load.
Who selects the motor?
It usually falls to the mechanical engineer who is typically very uncomfortable with the task. In an effort to insure success, the motor is invariable oversized and there are no controls specified. Some mechanical engineers are able to make the appropriate calculations or use a sizing software package to define the work in terms of time. Sometimes a time/displacement profile is generated in a motor sizing software application for servos, but these tools don’t exist for general purpose motor control.
The controls engineer typically has little knowledge of how to control the motor. If the time displacement curve exist, then acceleration values can be integrated into the control system. Otherwise, acceleration constants are arbitrarily applied since the controls engineer has no background in mechanical engineering to calculate the demand for torque.
The electrical engineer does not have a basis to communicate questions for the mechanical engineer without the knowledge that Current equals Torque. The mechanical engineer is not able to define the controls problem adequately unless there is a time/displacement profile which is never used for AC motors.
There’s a disconnect here, and it’s not in the circuit protection scheme.
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