Small and powerful DC motors are critical to the development of ever more highly integrated systems. These motors are driving technology in many different sectors, from medical and laboratory technology to aerospace, robotics, optics and photonics, as well as industrial machinery and equipment in general. But the small motors only mature to an application-relevant drive or positioning system when combined with other components, such as gearheads, encoders and motion controllers. Making the right choice is fundamental for reliable operation.
All components must be compatible with the motor and meet its requirements. In the worst case, selecting the wrong controller can destroy a motor in no time. When selecting a suitable motion controller for a drive system, it is important to answer a few questions first. For example, the movements that are to be carried out must be established, and it must be defined what this means in terms of motor control requirements. Is the drive working continuously or in start-stop mode? Is precise positioning required? What type of load will the drive be moving? What are the load cycles? Is a gearhead required? Which motor is best suited for the application? The motion controller is then selected based on the answers. And it may get interesting, because not every motion controller suits every motor. DC-micromotors in particular have unique requirements due to their design.
Risk of overheating
At the heart of the DC miniature and micromotors from FAULHABER is the patented, self-supporting, coreless rotor coil with skew-wound design and brush commutation, which rotates around a fixed magnet. This motor is also often referred to as a bell-type armature motor due to its look. Its design not only has many practical benefits, it also influences the selection of the motion controller.
No cogging torque forms due to the symmetrical air gap, which enables precise positioning and excellent speed control. The ratio of load to speed, current to torque, and voltage to speed is linear. And as almost the entire motor diameter can be used for the winding, the motors achieve higher power and torques for their size and weight compared with conventional designs. The rotor’s low inertia also guarantees an extremely low electrical time constant. The motors can thus be operated very dynamically and heavily overloaded. Triple continuous torque in overload mode is quite common and easily possible for servo applications, as long as the temperature of the motor winding is monitored. But motors with a diameter of only 22 mm or less don’t have an integrated temperature sensor. There simply isn’t enough space. So if just any controller is connected to a microdrive, in the worst case the coil may be completely burnt up before any heat is even noticed on the outside.
Problems like these can be avoided with motion controllers from FAULHABER, which were developed for the requirements of mini and micro drives and tested under real operating conditions. They ‘estimate’ the winding temperature for the respective motor type using models of varying complexity. This means that the full dynamic range of the motor can be exploited, for example for fast positioning processes. The current is also limited before the winding overheats. The parameters required are conveniently transmitted to the drive controller with the “Motor selection dialogue” of the FAULHABER Motion Manager.
Additional information about thermal integration in the application can be used in the models that are stored in the controllers for further improvement. How well is the motor cooled? Is it necessary to limit power due to high ambient temperatures? Is a gearhead and encoder used? With additional information like this, maximum motor power can also be used with, e.g. a drive that works cyclically in a climatic chamber, in that the motor controller keeps track of the ambient temperature parameters from the climatic chamber control within the models stored. The same applies if the load cycles are known. The motor can then often be smaller in design, which is an advantage especially when used in mobile devices.
Due to the low electrical time constant, which benefits dynamic processes, additional losses may occur due to the pulse width modulation (PWM) that is common in drive controllers. The typical electrical time constants of FAULHABER cbell-type armature motors are about 10 µs. For PWM frequencies below 50 kHz, the continuous torque specified in the data sheet is no longer achievable in many cases, or the motor may overheat. That is why it is important that the PWM frequency is sufficiently high when selecting a motor controller. For FAULHABER motion controllers, this is between 78–100 kHz, depending on the type. Due to the type of modulation, up to 200 kHz act on the motor, which suits the requirements of the small motors.
Powerful and extremely miniaturized
The motion controllers of the MC V3.0 family, which have been tried and tested for years, have limited usability for the micromotors from FAULHABER due to their size and the resolution of the integrated motor current measurement. This is where the new MC 3001 B/P comes in: The first motion controller that is perfectly suited to smaller servo drives, both in terms of its size and the resolution of the current measurement. With a maximum supply voltage of 30 V, the motion controller sized 16 x 27 x 2.6 mm (W x L x H) achieves a continuous current of 1 A and a peak current of 5 A. At lower supply voltages, such as in 12 V systems, continuous currents of up to 2 A can also be easily achieved. At the same time, they do not compromise on function compared with their large family members. The I/O options and encoder interface are the same as the rest of the product family. USB, RS232, and CANopen are available as communication interfaces. A compact EtherCAT interface can then also be provided via a customer-specific carrier board (motherboard).
The controllers are available in two variants: The model with flat board-to-board connectors (MC 3001 B) is ideal when several drive controllers are combined on one carrier card. The MC 3001 P variant features a plug connector with a 2.54-mm grid over three sides. It is easy to integrate into your own configuration, e.g. for multi-axis applications in laboratory automation. Now, there are finally powerful motion controllers for even the smallest DC drives from FAULHABER, perfectly matched to the motors both in terms of size and function.
For more information visit www.faulhaber.com/en/products/drive-electronics/motion-controller/
