Flicker-free illumination apparatus

1. A flicker-free illumination apparatus ( 28 ) for a code reader ( 10 ), the apparatus comprising:

an illumination control ( 26 ) which is configured for a pulsed operation with an illumination intensity varying between light pulses ( 30 ) and pulse pauses ( 32 );

wherein the ratio of illumination intensity of the light pulses ( 30 ) to illumination intensity during the pulse pauses ( 32 ) is at most 10/1;

wherein a pulse frequency of the pulsed operation of alternating light pulses ( 30 ) and pulse pauses ( 32 ) is in the range from 1 Hz to 100 Hz; and

wherein the illumination control ( 26 ) is further configured to maintain a non-zero illumination intensity during the pulse pauses ( 32 ), such that a basic intensity ( 34 ) remains.

2. The illumination apparatus ( 28 ) according to claim 1 ,

comprising a plurality of illumination units ( 36 , 38 ), wherein the illumination units ( 36 , 38 ) are light emitting diodes, laser diodes or respective illumination apparatuses of different code readers ( 10 ) of a reading system.

3. The illumination apparatus ( 28 ) according to claim 2 ,

wherein the illumination control ( 26 ) is configured to activate and deactivate a first subset of the illumination units ( 36 ) with a pulse frequency and to maintain continuous operation of a second subset of the illumination units ( 38 ).

4. The illumination apparatus ( 28 ) according to claim 2 ,

wherein the illumination control ( 26 ) is configured to deactivate a first subset of the illumination units ( 36 ) during the pulse pauses ( 32 ) and to reduce a second subset of the illumination units ( 38 ) to a non-zero illumination intensity ( 34 ) during the pulse pauses ( 32 ).

5. The illumination apparatus ( 28 ) according to claim 2 ,

wherein the illumination control ( 26 ) is configured to activate and deactivate a first subset of the illumination units ( 36 ) and a second subset of the illumination units ( 38 ) in a staggered sequence.

6. The illumination apparatus ( 28 ) according to claim 1 ,

wherein the illumination control ( 26 ) is configured to generate the basic intensity ( 34 ) by small light pulses at a pulse frequency higher than human perception.

7. The illumination apparatus ( 28 ) according to claim 1 ,

wherein the ratio of illumination intensity during the light pulses ( 30 ) to illumination intensity during the pulse pauses ( 32 ) is at most 4/1.

8. The illumination apparatus ( 28 ) according to claim 1 ,

wherein the illumination apparatus ( 28 , 36 , 38 ) transmits light in a visible spectrum.

9. A camera-based code reader ( 10 ) comprising

a flicker-free illumination apparatus, the apparatus having an illumination control ( 26 ) which is configured for

a pulsed operation with an illumination intensity varying between light pulses ( 30 ) and pulse pauses ( 32 ), wherein a pulse frequency of the pulsed operation of alternating light pulses ( 3 ) and pulse pauses ( 322 ) is at most 10/1; and

to maintain a non-zero illumination intensity during the pulse pauses ( 32 ), such that a basic intensity ( 34 ) remains, wherein a pulse frequency of the pulsed operation of alternating light pulses ( 30 ) and pulse pauses ( 32 ) is in the range from 15 Hz to 85 Hz; and

wherein the camera-based code reader ( 10 ) comprises an image sensor ( 24 ) for taking images of objects ( 14 ) with codes ( 20 , 22 ) to be read and an evaluation unit ( 26 ) for the decoding of code data from the images.

10. The code reader ( 9 ) of claim 9 ,

the code reader ( 10 ) being a stationary code reader for reading codes in a relative motion of the code reader ( 10 ) and the objects ( 14 ) bearing the codes ( 20 , 22 ).

11. The code reader ( 9 ) of claim 10 ,

the code reader ( 10 ) being designed as a line camera that takes a respective image line during a light pulse ( 30 ), wherein the evaluation unit ( 26 ) is configured to stitch successive image lines to an image of the object ( 14 , 20 , 22 ).

12. A method for flicker-free illumination of a reading area ( 18 ) of a code reader ( 10 ), wherein the illumination intensity varies in a pulsed operation between light pulses ( 30 ) and pulse pauses ( 32 ), wherein a pulse frequency of the pulsed operation of alternating light pulses ( 30 ) and pulse pauses ( 32 ) is in the range from 1 Hz to 100 Hz; and

wherein the reading area ( 18 ) is illuminated with a non-zero illumination intensity during the pulse pauses ( 32 ), such that a basic intensity ( 34 ) remains, wherein the ratio of illumination intensity of the light pulses ( 30 ) to illumination intensity during the pulse pauses ( 32 ) is at most 10/1.