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Types of electronic control
Definition of terms in accordance with DIN VDE 0740, Part 1000?Handheld electric power tools, technical terms:
1Â Control electronics
Control electronics govern a type of speed regulation which can be manually pre-selected or adjusted with the help of electronic components.
Speed regulation by semiconductor
diode
In the following curve diagrams you can see the characteristic curve of alternating current.
The contents of a wave train is the electrical power which is delivered to the motor. By blocking off one half of a sine wave, the rotational speed is reduced accord-
ingly. The most suitable component for this purpose is the diode; it stops the current flow whenever the polarity in its p-n junctions is not in the correct direction. Consequently, at 50 Hz 50 times per second.
Diode switching, however, produces a sudden rotational speed increase or drop since only half the wave can either be added or blocked off. Therefore, this type of speed modulation is fairly uncommon today. Rotational speeds could be modulated much more smoothly if both half waves could be further subdivided into even smaller electric impulses. Electronic control can do just that.
This is done by either pushing the accelerator button in the handle grip, or by pre-selecting the desired speed with an adjusting wheel or a similar control button.
Speed modulation is obtained by using the phase control method, i.e. longer or shorter electric impulses in a wave train are transferred with the help of a thyristor or a triac.
Half-wave control
One half wave is modulated whereas the other half is transferred unchanged. With this type of control you can control the speed from 0 to approximately 70% which is followed by sudden acceleration to 100%.
Full-wave control
Both half waves are modulated, and thus the rotational speed can be continuously controlled without sudden jumps.
Electronic regulation adjusts the motor speed automatically. With this method, speed control is load-dependent and performed by electronic components, and not by hand.
Electronic regulation can be further equipped with a dial to pre-select different speeds.
Since the terms control and regulation are hard to distinguish, BOSCH has decided to use the term Constant-Electronic instead of electronic regulation.
Modern power tools are equipped with various types of electronic control to adjust the operational behaviour of machines to changing working conditions. From the many possible variations we shall only dicuss the following selection:
As a rule, mechanical speed changes in power tools can only take place in steps, whereas speed changes by electronic components can be continuous and stepless. In many tools you will find a combination of the two.
Electronic regulation
Regulation functions automatically and cannot be influenced by the user. It is always based on a comparison of actual and desired values, i.e. a sensor registers the current operational status and transmits it to a comparator.
Electronic regulation with permanent
programme, Constant-Electronic
A tachogenerator registers the current rotational speed. A comparator determines the ratio between actual/target values and, if necessary, adjusts the motor speed of, for instance, an angle grinder. Motors are designed to reach their nominal speed when the motor voltage is still low. The voltage difference between mains and motor voltage is used for regulation purposes. The elaborate tachogenerator can also be replaced by a less intricate gauge to measure the motor current or voltage.
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