The invention relates to a drive unit for objects to be wound on to and off a tube according to the preamble of claim 1.

Drive units including a combination of a shaft, a brake, a motor, and a gear, the combination being insertable into a tube, normally are called tubular drives. Such drives are for driving objects to be wound on to and off said tube, like sun blinds, roller shutters or cinema screens. It is also known that such drive units are combined with a manual override where the whole drive unit or tubular drive together with the tube is rotated by hand. To this end the currents for the motor and the brake are to be fed via collector rings from a fixed and normally wall-mounted part.

Such tubular drive is known e. g. from DE 298 18 023 U1 .

Such tubular drives normally are combined with end switches in order to avoid damages. But often it would be desirable not only to detect the end positions but also any position in between.

The object of the invention therefore is to design the drive unit such that during normal operation also positions between the end positions can be detected and that it is not damaged during a manual override.

This object is solved according to the invention by a drive unit according to the teachings of claim 1.

The basic idea behind is to use an incremental encoder whose (electronic) sensor is attached to the fixed part of the drive unit and where the counterpart of the sensor, which is not an active part, is attached to the moving part.

The use of incremental encoders in connection with fixed magnetic field sensors and moving magnets as well as the use of concentric collector rings arranged in a plane perpendicular to the shaft is known as such from DE 100 38 285 A1 .

Further embodiments of the invention are to be found in the subclaim and the following description.

In the following the invention will be described with reference to the accompanying drawings:

Figure 1

shows a first embodiment of a drive unit according to the invention.

Figure 2

shows a second embodiment of a drive unit according to the invention.

Figure 1 shows a combination of a brake Br, a motor Mo and a gear Ge on a common shaft Sh. It further shows a magnet Mg, two collector rings CR1 and CR2, two Hall sensors HA and HB, and leads +Mo/Br, -Mo/Br, +E1, -El, A, and B.

The combination of the brake BR, the motor Mo and the gear Ge is shown as being concentric to the shaft Sh, what is normal for such tubular drives. At the right-hand-side the shaft Sh is foreseen to drive the tube for winding on and off whatever object.

In this example motor Mo and brake Br are connected in parallel. They are connected between the leads +Mo/Br and -Mo/Br via the collector rings CR1 and CR2. Short-circuiting this leads activates the brake Bk, applying a DC voltage thereto activates the motor Mo.

When using a DC motor, one needs only two collector rings; otherwise at least three collector rings would be necessary.

In this example the two collector rings CR1 and CR2 are shown to lye in a plane, e.g. on a printed circuit board, perpendicular to the shaft Sh and concentric thereto. An other possibility would be to use cylinders concentric to the shaft.

The magnet Mg together with the two Hall sensors HA and HB build an incremental encoder. Another possibility of an incremental encoder could be a photo sensor in connection with a raster. In any case we have an active sensor and a passive counterpart thereof. There are enough known examples of such encoders and suitable evaluation circuits. They may include one single sensor part or more than one; they may include one single counterpart or more than one.

Normally when using such incremental encoders in connection with an electric motor the whole encoder is mounted within the housing of the motor and only the leads thereto are accessible outside. Here it is proposed to attach the sensor to the fixed part of the whole drive unit. The passive counterpart should be attached to the moving part, here the shaft Sh.

The active sensor here is powered by the leads +El and -El, normally taken from the electronics evaluating the output signals; the output signals are accessible via the leads A and B.

As the active part of the encoder is unmovable whereas the passive part is rotatable, necessarily the plane carrying the collector rings is traversed.

In the example of figure 1 the shaft Sh traverses this plane, in the example of figure 2 the leads +E1, -El, A, and B together with some support for the sensor traverse this plane. The choice there between may be made in view of an easy assembly. As the plane carrying the collector rings normally is not magnetic, the sensor could even be on one side and the magnet on the other side of this plane.