DE3142819A1 - Vibration damping for a stepping motor - Google Patents

Abstract

Vibration damping is proposed for electric motors which have no commutator, especially multi-phase stepping motors, servo motors etc., the medium of specific viscosity, which is suitable as a liquid damper, being arranged directly between the rotor and the stator of a stepping motor and the rotating motor output shaft being able to be sealed by means of a ferro-fluid sealing element.

Description

Vibration damping for a stepper motor

The invention relates to the vibration damping of brushless electrical Motors, especially multi-phase stepper motors, servomotors, etc., where the as Liquid damper suitable means of certain viscosity directly between the rotor and stator is arranged.

The requirements with regard to short settling times for motors, who work in intermittent operation (e.g. stepper motors in start-stop operation), have increased due to faster positioning, especially with regard to the positional accuracy and the vibration behavior of the moving mass.

Especially in the area of broader data technology with a large number of devices and machines in which data carriers, optical parts, closures, write heads, etc. have to be moved briefly, for example in scanners, laser imagesetters, geometric Drawing machines, EDP devices, etc., it comes to the highest positioning accuracy and stability of an approached position.

The vibration behavior of the stepper motors used for this can in particular, the decay time of an approached position is an impairment lead to a certain expected result or must be taken into account as a settling time Find.

A suitable measure to dampen vibrations and thus shorten them the settling time would bring significant benefits.

Means for damping electric motors, in particular stepping motors are known either as external mechanical damping such as friction clutches or liquid damper or by means of electrical / electronic circuits as Eddy current clutches (DE-PS 21 61 112) or other circuits, these internally are effective.

It is known that the stepper motor shaft on its otherwise free, stored one To extend the end and there an external damping device, for example one To attach a friction clutch or an additional oil-filled container (DE-OS 22 49 648).

The disadvantage here is that this creates an additional mass moment of inertia on the motor shaft, which in turn reduces the effect to be achieved.

The additional accommodation of an oil damper is necessary on the one hand the design change of the output shaft of the engine, and on the other hand must be a additional space requirements can also be taken into account constructively. An afterthought Converting a stepper motor is therefore only possible to a limited extent.

From DE-OS 25 39 437 a multiphase stepper motor is known, which has a sealed drive area with stator / rotor and in which the Output shaft is guided to the outside via a gear chamber filled with oil.

Here, too, additional mechanical components are required for the special Sealing and achieving a damping effect through a special design of the Transmission part. So increased turn the total moment of inertia.

Finally there is an internal rotor damping of a stepper motor known, in which the rotor consists of a toothed tube and a consists of a soft iron core stored in oil. The core acts here as a vibration damper and is also used for the necessary flow guidance. Due to this, must be between Tube and core can be provided a very narrow gap and thus a reduction in the actual damping effect, if not an unstable behavior of the viscous Fluid occurs.

It can therefore be assumed from a known prior art that Fluid dampers on stepper motors require additional mechanical devices.

In contrast, the invention has set itself the task of providing the best possible Show damping to reduce the tendency of stepper motors to oscillate without while increasing the total moment of inertia formed from the rotor and the external load and to keep the previous proportions of undamped stepper motors unchanged.

This task is carried out by the characterizing part of the claim 1 specified features solved.

According to the invention, stepper motors can be surprisingly simple Manner are damped in that the damping means surrounds the rotor, i.e., the stepper motor is filled directly with a damping fluid. As a dampening agent In this case, a silicone oil with adapted viscosity and the following basic properties has proven itself proven: 1. Not electrically conductive 2. Neutral to metals, Non-metals 3. Lubricating and slidable 4. Resistant to temperature fluctuations 5. Good thermal conductivity 6. Carrier for magnetic particles (as ferrofluid) 7. Extreme low vapor pressure The advantages resulting from the invention are substantial It can be seen that there is minimal additional mass moments of inertia for damping stepper motors occur by adding a damping device. This becomes theoretical shortest setting time achieved.

Another advantage is the now improved heat dissipation by directly filling the stepper motor with an appropriate liquid, as will be described in more detail below.

The invention also achieves a sharp decrease of the noise level, not only on the stepper motor itself, but there is also a noise reduction of the parts driven by the motor shaft (gears, Spindles, etc.). This is especially true for motors with a certain step frequency during continuous operation, when "running up" or in an irregular working state, advantageous.

As a result of the invention, it is now possible to be already in use located or structurally provided stepper motors in which a damping it becomes necessary to retrofit or replace it afterwards, as there is no change the external proportions of stepper motors is done; sometimes even the engine can original can be reused.

The present invention is intended below on the basis of an example and are described and explained in more detail by drawings. It shows: Fig. 1 schematically a stepping motor of known design, Fig. 2 the vibration behavior of an undamped Stepper motor, Fig. 3 shows the vibration behavior of a now damped stepper motor.

Fig. 1 shows the most essential parts of a stepping motor known Design type. The motor shaft 1 is connected to the rotor 2, the shaft 1 by means of a front bearing 3 on the flange 4 and by a rear bearing 5 on the cover 6 is stored. As is known, the stator 7 consists of windings 8 with corresponding windings Laminated stacks and is attached to the housing 9.

Such a stepping motor can be constructed as a multi-phase motor be, for example, as a 5-phase stepper motor with up to 9000 steps per revolution.

Such motors are used wherever in the shortest possible time discrete paths have to be covered with absolute positioning accuracy.

According to the invention, vibration damping is now used directly in the A special liquid 10 is filled in between the rotor and stator. Preferably a silicone oil with a certain calculated viscosity is used. Has silicone oil all those excellent properties, which are electrical, chemical, mechanical and heat wise needed to act as a dampening agent directly between Stator and rotor act too, and can act as carriers for magnetic particles serve (ferrofluid for controlled damping and / or magnetic field guidance). Next to the achievable damping effect, as will be explained in more detail below, were the use of silicone oil improves further engine properties. First the practically proven oil causes an improved heat transfer to the housing of the motor, especially during continuous operation under load. The complete swirl the oil gets through the serrated or grooved surface of the rotor and the also uneven stator surface supported.

Furthermore, the direct oil damping of the rotor has a significant effect Noise reduction of the whole engine; a significant decrease in structure-borne sound transmission is observed.

The viscosity of the liquid should depend on the type of use of the stepper motor, i.e., adapted to the mass load on the motor shaft. For one use case with little mass loading, the viscosity will be higher, also in adaptation to the operating mode and duration of the respective stepper motor type.

Stepper motors are usually constructed in such a way that the motor shaft is in Ball bearing is mounted. In the use made according to the invention with With a silicone oil directly in the engine compartment, the ball bearings do not get through in any way adversely affects the silicone oil, but the outwardly open bearings should now by means of a commercially available simple rubber seal or by means of a ferrofluid seal be provided.

For the motor according to FIG. 1, the bearing 3 should correspond to the shaft 1 must be sealed.

From what has been said so far, it is therefore true that already used Stepper motors, the vibration behavior of which is particularly disturbing, now on simple Interchangeable and even directly re-usable.

In connection with the invention, it is also proposed instead of sealed ball bearings using a ferrofluid sealing element. These sealing elements with ferro seals are ideally suited for sealing shafts, with no wear effects appear. The controllable friction losses can be extremely low, and there is a perfect seal even with faster rotations. Included the bearing friction is also used as damping. Such sealing elements exist from a magnetic liquid and small magnetite or ferrite particles of about 10 nm and by means of an externally applied field of a magnet in the gap to be sealed is sucked. Such sealing elements are in place of the bearings 3 and 5 of the engine of FIG. 1 are provided.

FIGS. 2 and 3 now show the oscillation behavior of a stepping motor without damping (Fig. 2) and with damping according to Fig. 3.

It became a 5-phase stepper motor with a mass moment of inertia less than 70 gcm2 on the motor shaft. The motor has 500 steps per revolution and was driven at a frequency of 800 Hz ... 3 KHz. The figures show the Motor in reversible operation. The angle of rotation was 28 steps in each case, accordingly approx. 21 O.

According to FIG. 2, the oscillator image shows the course of the movement for a forward movement through line 12 and a return movement by the line 11. The left vertical reference edge 20 is the respective starting point, and you can see that the new position has been reached at points 13/14 and the engine stops. The continued swinging is clearly recognizable.

Fig. 3 shows the same motor now with a damping the invention. The curves 15 and 16 now show an almost ideal straight line Increase and absolute standstill after the engine has stopped (points 17, 18); at controlled Motors, the theoretically shortest setting time is achieved.

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Claims (4)

P a t e n t a n s p r ü c h e 1. Vibration damping for a stepper motor, with a liquid damper acting on the predominantly cylindrical rotor, d u r c h e k e n n n n e i c h n e t that this is suitable as a liquid damper Means (10) determined calculated viscosity directly between rotor (2) and stator (7) is arranged. 2. Vibration damping according to claim 1, d a d u r c h g e k e n n indicates that the liquid damper is a chemically inert liquid (e.g. a silicone oil) of a certain viscosity. 3. Stepper motor according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the outgoing power wave for rotating movements compared to the liquid-filled engine is sealed by means of a bellows. 4. Stepper motor according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the rotor and / or the outgoing power shaft for rotating movements is stored in at least one ferrofluid sealing element.