Hi Misan,
I read the paper that you linked to, and I can see a couple of major obstacles to bringing the price point of a brushless DC motor with closed loop positioning based on linear hall effect sensors down to the $15 price point that we are used to with our basic NEMA 17 steppers.
1. The price of adding the many required linear hall effect sensors to any brushless DC motor assembly is not negligible. First, quite a few sensors are required, second, they must be precisely positioned, and third, each additional sensor requires wires which have to connect to the closed loop control circuit. And of course, each sensor/wire/component adds one more failure point to a mechanical device designed to operate thousands of hours. All that is not easy to do cheaply.
2. The closed loop control circuit for each brushless DC motor appears to require as much (real-time) processing power or even more than our very basic 8-bit AVR MCU - that presently controls an entire 3D printer - can provide. So basically for a five-stepper Prusa i3 we would require five 32-bit MCUs just for the control loops. And again, we are adding quite a few more failure points to our 3D printers.
3. One of the details that the paper brushes over (pun intended) is that each individual linear hall effect sensor needs to be calibrated separately and requires a properly designed analog amplifier circuitry for signal conditioning. Again, more costs and more failure points.
Of course I find the idea of closed loop control of rotary or linear motion actuators extremely attractive, but I am guessing the reason servo motors for e.g. CNC applications are so expensive is that there is no known way to make them any cheaper.
I read the paper that you linked to, and I can see a couple of major obstacles to bringing the price point of a brushless DC motor with closed loop positioning based on linear hall effect sensors down to the $15 price point that we are used to with our basic NEMA 17 steppers.
1. The price of adding the many required linear hall effect sensors to any brushless DC motor assembly is not negligible. First, quite a few sensors are required, second, they must be precisely positioned, and third, each additional sensor requires wires which have to connect to the closed loop control circuit. And of course, each sensor/wire/component adds one more failure point to a mechanical device designed to operate thousands of hours. All that is not easy to do cheaply.
2. The closed loop control circuit for each brushless DC motor appears to require as much (real-time) processing power or even more than our very basic 8-bit AVR MCU - that presently controls an entire 3D printer - can provide. So basically for a five-stepper Prusa i3 we would require five 32-bit MCUs just for the control loops. And again, we are adding quite a few more failure points to our 3D printers.
3. One of the details that the paper brushes over (pun intended) is that each individual linear hall effect sensor needs to be calibrated separately and requires a properly designed analog amplifier circuitry for signal conditioning. Again, more costs and more failure points.
Of course I find the idea of closed loop control of rotary or linear motion actuators extremely attractive, but I am guessing the reason servo motors for e.g. CNC applications are so expensive is that there is no known way to make them any cheaper.