Overall Motion Control

You have a motor, such as a permanent magnet DC motor found on toys, and you know that if you connect said actuator to a battery or some power source, the motor shaft spins. This mechanical spin is used to move your RC car wheels, spin the DVD player media disc, spin the metal disc on Hard Disk Drives, spin your clothes on the washer and drier, spin the auger that in turns deliver ice at your refrigerator with an ice maker, moves arms and legs on toy or industrial based robots, allows for your e-bike to run without pedaling and your scooter to move forward without kicking and pushing, opens your garage gate, etc.

Motors are everywhere! Are very useful and not so hard to use. But how does a system using motors work? What do we need to understand in order to get me some motors working properly on my next cool application?

Most motor applications use a very simple implementation I like to call Power-Amplifier-Motor (Lets call it PAM). With PAM systems, there is a power source (either a battery or wall outlet derived power supply), which delivers power to the motor. How much power and how fast is this power delivered to the motor is controlled with the amplifier. The amplifier is often an H Bridge power stage often called the Power Driver which is then controlled by some form of logic (FPGA or Microcontroller).

The amplifier receives weak signals from some sort of controller, let say the remote control receiver on your RC car, and then transform this input command into a much more powerful signal the motor can use to move accordingly. As a result, the weak signals from the remote control will translate to speed and direction on your RC car. The same applies to practically every other application using this simple method of interfacing.

There are some other applications, however, which require a degree of control totally different than the RC car example. In the RC car, you apply the control. If you want the car to move faster, you move the lever further. If you want the car to move slower, you retract the lever. How much you move the controlling lever translates into how fast the car moves. But what happens when a human can not be employed at all times to control the speed of the motor?

Per example, on your washer and drier, the idea is for no humans to be involved. If we had to control the speed of the motors, we might as well wash our clothes by hand! We want this machine to do all the job and for us to return later when the task at hand is complete. In this case, we need a controller that can close the loop. These systems are often called Closed Loop Motor Controllers (CLMC) and their level of complexity can range from very simple to considerably much more complicated than the PAM case.

CLMC's can be as complicated as to require the use of an entire computer to derive said control. Per example, industrial robot applications utilize very powerful computers to make sure every single detail of the motion control is performed to perfection, improving both accuracy and precision.

On this blog, I will eventually detail aspects that can be used to work on highly complex CLMC's, but we will get busy with the simple PAM's first. Later we will add some simple Closed Loop mechanism as said approach is more than enough to tackle a great deal of the motor control applications out there.