CH653498A5 - Method for controlling an electric motor - Google Patents

Description

The invention consists in a method for regulating an electric motor with different thermal loads and in an arrangement for carrying out the method.

With electric motors, it is often the case that very different thermal loads on the motor winding occur in one workflow. So far, with these different thermal loads, only an attempt has been made to prevent the windings from overheating. There are two ways to do this. In one process, the motor is designed so that the maximum permissible temperature is not exceeded even in the worst case. In addition, overload protection e.g. be provided in the form of a fuse. Another method is used when particularly extreme load combinations rarely occur. Here is a way to automatically turn off the engine when these extreme circumstances occur.

The disadvantages resulting from these solutions are obvious.

In both cases, a motor must be selected that can withstand high thermal loads, although these are not used for most of the operating time. Of course, this entails high costs. In addition, in the one case it must be accepted that the engine is switched off under extreme loads and the workflow is interrupted.

The object of the invention is therefore to provide a method which, even though the motor is only designed for a medium load, allows uninterrupted operation, and further gives the possibility of regulating it at low motor temperatures in such a way that by utilizing the thermal reserves accelerated workflow is achieved.

The object is achieved by the characterizing features of patent claim 1. An arrangement for carrying out the method according to the invention is characterized in claim 2.

The main advantage of the invention is that, while avoiding thermal overloading, an electric motor that is undersized per se can be regulated in such a way that uninterrupted operation is possible with changing thermal loads, and that the workflow is accelerated if thermal reserves are available.

The details of the invention are explained in more detail below using an example and the drawings. Show it :

Figure 1 is a representation of a workflow with different thermal loads;

FIG. 2 shows the workflow from FIG. 1 that is regulated as a function of the engine temperature;

Figure 3 shows a circuit for performing the method.

For a more detailed description of the invention, the positioning of a type wheel in typewriters and similar office machines was selected as an example, since the relationships can be illustrated very well here. In this example, it is assumed that the text to be printed is retrieved from a memory.

The letters on the type wheels are usefully arranged in such a way that characters appearing frequently in a statistically middle text are in a certain circumferential area of the type wheel. For the drive motor, this means that it is only slightly thermally stressed for the majority of the operating time, but must be thermally very strong when positioning letters that are far apart on the circumference of the type margin over longer periods of time.

Such a workflow is now shown in FIG. 1 in the form of an energization diagram I, in which a temperature curve T and a maximum permissible temperature Tmax are additionally shown. zui. is drawn.

For better illustration, only three different energization times, a very short U, a medium ti and an extremely long to were selected, each put together in a series, and arranged one after the other. The pause 35 tA between the energization times was selected so

that a steady-state temperature 1 occurs in the steady state during the mean energization times ti, which is just below the maximum permissible temperature Troax. perm.

It can now be clearly seen in FIG. 1 that the thermal reserves of the motor are not used until the steady state with steady-state temperature 1 is reached and in the region of the very short energization times t2, which lead to steady-state temperature 2. In the area of extremely long energization times t3, however, the temperature rises above the maximum permissible value to a steady-state temperature 3, which leads to the destruction of the winding.

This means that a motor would have to be selected for uninterrupted operation in such a way that its maximum permissible temperature is slightly above the steady-state temperature 3 which arises when the motor is subjected to the longest flow time for a longer period of time.

Another way of protecting the motor against excessive temperature is to increase the pauses between the energization times so that a steady-state temperature that is lower than the maximum permissible temperature arises in the worst case.

The result is that in one case the engine costs are considerably higher, or in the other case the writing speed drops.

FIG. 2 shows the energization diagram I from FIG. 1, in which, however, the cooling time between the energization times of the motor is regulated as a function of two switching temperatures esTschi and TSch2.

The control takes place in such a way that a pause tx below the switching temperature TSchi, a pause ty above the switching temperature Tschl and a pause above the switching temperature TSch2

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Pause tz is switched between the energization times.

FIG. 2 now makes it clear that the temperature level is increased by switching on the shorter pauses tx between the energization times where there are thermal reserves according to FIG. A higher writing speed is thus achieved using the thermal reserves. It can also be seen that the engine temperatures which, according to FIG. 1, are higher than the maximum permissible temperature Tmax. CLOSE | "can be brought to a level below the maximum permissible temperature Tmax by switching on longer breaks tz between the energization times.

Since, as already mentioned, short positioning operations of the type wheel, which necessitate a short energization time of the drive motor, have to be carried out for the majority of the operating time, the increase in the writing speed is much more pronounced than is shown in FIG. 2.

With regard to the representations in FIGS. 1 and 2, it should be noted that the actual conditions are shown in a coarser manner, since, for better illustration, a substantially lower thermal time constant was assumed than occurs in the arrangement described. However, that does not change the principle.

It must also be stated that this temperature-dependent motor control can be significantly improved by introducing additional switching temperatures or cooling times, regulating the current intensity, regulating the energization time, and additionally influencing the regulation by evaluating the next positioning process.

Depending on the application, it is of course conceivable that only one or a combination of the control options described above is used.

FIG. 3 shows a circuit for carrying out the method.

A voltage Ui is tapped at a voltage divider, which contains a fixed resistor 4 and a parallel circuit comprising a temperature-dependent resistor 5 and a linearization resistor 6. This voltage io is converted in a voltage-frequency converter 7 into a frequency fi corresponding to the voltage Ui and passed on to a microprocessor circuit. Through its program, this acts on a motor control unit 9, which controls the motor 10 in such a way that thermal reserves 15 are used without permitting the windings to become too high. The circuit for carrying out the method can of course be designed differently from the example in FIG. 3.

With the above-described method, 20 a possibility is created to regulate an electric motor, of whatever type, which is exposed to different thermal loads and, for cost reasons, was only designed for a medium load case, in such a way that using the thermal reserves and without to exceed a maximum permissible temperature of 25, a workflow is carried out without interruption in the shortest possible time.

Of course, it is also possible to use the method according to the invention in arrangements other than the positioning device of a type wheel described in Example 30.

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2 sheets of drawings

Claims (2)

653 498 2 PATENT CLAIMS 1. A method for regulating the workflow of an electric motor with different thermal loads, characterized in that the electric motor (10) has a temperature sensor (5), the physical state change of which is evaluated by an electronic circuit (7, 8), and in dependence The electronic circuit (7, 8) regulates the cooling times between successive energization times of the electric motor (10) by correspondingly controlling a motor control unit (9) in such a way that the workflow is carried out without interruption while avoiding thermal overloading of the electric motor (10). 2. Arrangement for performing the method according to claim 1, characterized in that a voltage divider consisting of a fixed resistor (4) and a parallel circuit comprising a temperature-dependent resistor (5) and a linearization resistor (6) is included, on which a voltage Frequency converter (7) tapped a voltage, converted into a corresponding frequency and passed on to a microprocessor circuit (8) which controls a motor control circuit (9).