The demand for longer life motors is growing in all industrial sectors. If a mechanically commutated DC motor reaches its limits, it is time to switch the application to brushless DC motors. Only a year ago, the manufacturer and distributor of compact, highly integrated, electric drives and controls koco Motion Brushless DC motors added to its portfolio. Today he already offers one Product spectrum, which leaves almost nothing to be desired.
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"Brushless DC motors have been around since the end of the 70 years, at that time mainly installed in fans. With the miniaturization of the electronic components, they are gradually gaining ground in many other applications. Today, they are used in large quantities everywhere where long service life is required, "says Gerhard Kocherscheidt, Managing Director of Koco Motion GmbH in Dauchingen. "We introduced them to us last year because the market is increasingly asking for a long service life and freedom from maintenance for this type of drive," says Kocherscheidt.
The designation of brushless DC motors is versatile: brushless DC motor, short BLDC or BL motor as well as electronically commutated motor, short EC motor. In the brushless DC motors, the mechanical contacts in the commutation, ie the brushes, are replaced by a contactless, electronic system. This eliminates some disadvantages and drastically increases the reliability and the life of the engine, which now mainly depend on the life of the shaft bearing. In addition, these now maintenance-free engines do not mind if they are overloaded by higher speeds and short-term torque peaks. They offer excellent speed control properties and only develop small interference signals. In addition, they are suitable for operation in harsh environments. The brushless DC motors have versions with a grooved laminated core or as a slotless design. The latter are iron-free and offer numerous advantages over iron-powered engines, which are paid for at a slightly higher price: there are no cogging torques and iron losses. The rotor has a lower inertia, runs quieter and vibration less and can be better positioned.
Structure and mode of actionIn the case of brushless DC motors, the force exerted on current-carrying conductors, ie the commutation, no longer takes place mechanically via the brushes but electronically. The active elements are arranged in the opposite way as in the brushed motor: The permanent magnets are fixedly connected to the rotor while the windings are housed in the stator. When an electric current flows in the windings, a magnetic field is formed in the stator, which attracts the permanent magnets in the rotor according to the polarity. This creates a force effect that generates a torque on the permanently excited rotor. After the rotor has aligned according to the magnetic field generated in the stator, the rotation would end. To prevent this from happening, the current flow in the windings must be switched by an electrical circuit so that the generated magnetic field continues to rotate. Three-phase systems are commonly used in EC motors.
Commutation of the EC motorEC motors offer the possibility to carry out the electronic commutation depending on rotor position and speed as well as torque. There are several ways to capture rotor position and speed:
In sensorless commutation, the rotor position is detected via the reverse voltage induced in the coils of the stator. The rotor starts in any direction, with the electronics detecting at zero crossing if it's the right one. If that is the case, it will be accelerated further. If the motor turns in the wrong direction, the direction of rotation is corrected and then accelerated further. This type of commutation is very well suited for endurance runners at high speeds, such as those found in fans or propeller drives in model helicopters.
In sensor-controlled commutation, three Hall sensors offset by 120 detect the position of the rotor by giving corresponding switching signals. According to this position information, the windings are controlled by suitable power drivers of the control electronics, which generate a torque in the rotor. The sensor-controlled commutation also works at very low speeds or at standstill. Usually, during this commutation in three or more phases not all phases are energized simultaneously. At least one phase remains de-energized here at any time. With this principle, highly dynamic drives can be realized and the speed controlled. Positioning is only possible with the coarse resolution of the Hall sensors. The sensor-controlled commutation, for example, is predestined for use in small pumps, scanners or propeller drives.
Another principle is the commutation via Hall sensors together with high-resolution encoders: This version requires a more complex control with position controller. With it, it can be positioned very accurately according to the encoder resolution and regulated as highly dynamic as with a servo drive. Applications for this most complex type of commutation can be found, for example, as positioning drives in microscopes and medical devices as well as in card readers.
For demanding applications, the vector control offers. In contrast to operation on the three-phase network, the rotor position does not adapt passively to the voltage and the torque, but the voltages of all phases actively adjust to the rotor position and the desired torque. For this purpose, all phases are driven with sinusoidal voltage and energized at the same time.
Perfectly happy-portfolioOver the last few months, KOCO MOTION has been gradually expanding the brushless DC motor program, offering electronically commutated DC motors with a slotless stator and iron-coupled BLDC motors. Just how versatile the portfolio is is shown by the partners with whom the Dauchinger drive specialists work together: "We have exclusive contracts with exclusively certified companies like Constar, Hengdrive, Dinko and Yunkong as well as a cooperation with Leadshine Our current product range offers solutions for most all applications ", says the managing director.
Ironless DC motors"One of our latest products is a miniature servo system, consisting of a slender brushless servomotor with encoder and planetary gearbox," says the CEO, referring to the innovation first introduced at the recent SPS IPC Drives. The miniature servomotor measures only 12 mm in diameter and achieves a continuous power of 1,1 W. The encoder has 256 lines, 2 channels and zero index. The planetary gear is designed for a permissible continuous torque of up to 0,2 Nm. The new drive system is already being used in medical devices such as the multi-leaf collimator - a device that is attached to a linear accelerator in radiation therapy in order to adapt the treatment beam to the shape of the object to be treated.
The portfolio of manufacturing partner Constar, a developer and manufacturer of DC bell motors, brushless DC motors and custom DC motors, now comprises eleven series, ranging from 10 mW with a diameter of 4 mm to 100 W with a diameter of 75 mm. The idling speeds are 4000 to 50.000 min-1, The ironless or slotless BLDC motors are available with mechanical and electronic commutation. The brushless motors with slotless stator are usually 3-phased. They are available with and without Hall sensors. In the version without the Hall sensors, one uses the electromagnetic force (EMF) for speed detection. Equipped with Hall sensors and / or encoders, they are suitable for applications requiring reversal of speed and direction and positioning.
Except in medical devices, such brushless DC motors are found in instrument making, electric tools, small household appliances, and airplane and ship models.
Iron-tinged DC motorsThe iron anchor BLDC engine program comes exclusively from the Chinese manufacturer Hengdrive. It comprises ten models in the diameter range 16 to 68 mm with lengths from 18 to 72 mm. The rated voltages from 6 to 48 V and 220 V AC allow power outputs from 0,5 to 67 W. Equipped with integrated electronics for stepless speed control from 0 to 100% via PWM (Pulse Width Modulation) or via the encoder signal reversible BLDC motors. In addition, the mostly 3 phased motors have a quick-braking function and offer high efficiency. Thanks to their simple construction, the Hengdrive engines are very reasonably priced. In addition, they offer a long service life of over 10.000 operating hours and have EMC-friendly as well as no electromagnetic interference. They simply work in their reversal direction and run very low noise and vibration. Dinko's iron-infused BLDC motors complete the program. With flange dimensions from 42 to 130 mm, they offer performances from 20 to 500 W and are all equipped with a Hall sensor and ball bearings.
The application options for the iron-anchor BLDC motors are incredibly versatile: for example, they are suitable for small drive tasks in household, medical and personal care equipment. The list can be continued in numerous ways with applications in the automotive, office technology, instrumentation, pumps, fans or security and monitoring systems as well as computer technology.