OPTICAL CODE READER

Abstract

An optical code reader (10) is provided that has a light transmitter (12) having a transmission optics (14) for transmitting a reading beam (16) in a reading region (18); a focus adjustment unit (28) for focusing the reading beam (16) in a distance range; a light receiver (24) for generating a received signal from the reading beam (20) reflected in the reading region (18); and an evaluation unit (26) to read code information from the received signal. In this respect, the focus adjustment unit (28) has a pivot arm (30) that holds the transmission optics (14) at a different distance from the light transmitter (12) in dependence on the pivot position of the pivot arm (30) and that has a moving coil unit (34) to pivot the pivot arm (30).

Claims

1. An optical code reader, the optical code reader comprising: a light transmitter having a transmission optics for transmitting a reading beam into a reading region; a focus adjustment unit for focusing the reading beam in a distance range; a light receiver for generating a received signal from the reading beam reflected in the reading region; and an evaluation unit to read code information from the received signal, wherein the focus adjustment unit has a pivot arm that holds the transmission optics at a different distance from the light transmitter in dependence on the pivot position of the pivot arm and that has a moving coil unit to pivot the pivot arm.

2. The optical code reader in accordance with claim 1, wherein the moving coil unit has a coil fastened to the pivot arm and a fixed-position permanent magnet in whose magnetic field the coil is arranged.

3. The optical code reader in accordance with claim 2, wherein the permanent magnet generates a homogeneous magnetic field.

4. The optical code reader in accordance with claim 2, wherein the permanent magnet has two magnet pairs that are arranged conversely to one another.

5. The optical code reader in accordance with claim 1, wherein the pivot arm is supported and arranged in the moving coil unit such that the pivot movement takes place perpendicular to the longitudinal extent of the pivot arm.

6. The optical code reader in accordance with claim 1, wherein the moving coil unit is arranged at an end of the pivot arm.

7. The optical code reader in accordance with claim 1, wherein the pivot arm is supported at its one end.

8. The optical code reader in accordance with claim 1, wherein the pivot arm is supported by means of a leaf spring.

9. A method of reading optical codes in which a reading beam is transmitted by a light transmitter through a transmission optics into a reading region and a received signal is generated in a light receiver from the reading beam received again to read code information from the received signal, wherein the transmission optics is focused by a focus adjustment unit in a distance region, in which method the focus adjustment of the focus adjustment unit takes place by pivoting a pivot arm that supports the transmission optics and that varies the distance between the light transmitter and the transmission optics; and the pivot arm is pivoted by a moving coil unit.

Description

[0019] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0020] FIG. 1 a simplified block diagram of a code reader with a focus adjustment that has a pivot arm and a moving coil unit;

[0021] FIG. 2 a three-dimensional view of an embodiment of a focus adjustment unit with a pivot arm and a moving coil unit; and

[0022] FIG. 3 a representation of a moving coil unit with a permanent magnet and its magnetic field as well as a live coil immersed therein.

[0023] FIG. 1 shows a simplified block diagram of a code reader 10. A light transmitter 12, for example having an LED or a laser as the light source, generates via a transmission optics 14, for example in the form of a lens, a reading beam 16 that is transmitted into a reading region 18. If the reading beam 16 is incident on an object there, the reflected or remitted reading beam 20 returns to the code reader 10 and is conducted to a light receiver 24 via a reception optics 22. A received signal is generated from the incident light of the remitted reading beam 20 there and is supplied to an evaluation unit 26. The evaluation unit 26 is also connected to the light transmitter 12 for its control.

[0024] To detect a code in the reading region 18, a scanning takes place by a scan mechanism, for example using a pivoting or rotating mirror that moves the reading beam 16 over the code region. This scan mechanism is not shown for simplification. If the laser beam 16 scans a barcode, for example, the amplitude of the received signal is modulated in a manner corresponding to the code bar. The evaluation unit 26 is therefore able to read the code information. It also recognizes when the received signal does not correspond to any code. The location of code regions and the reading of the code information is known per se and will therefore not be explained in more detail.

[0025] It is required for a reliable detection of the code information that the code is at a spacing from the code reader 10 that lies within the depth of field range of the transmitting optics 14. In other words, the light spot generated on the code by the reading beam 16 should be sufficiently focused. To ensure this over a larger distance range, a focus adjustment unit 28 is provided that is likewise connected to the evaluation unit. Although it is conceivable to use the focus adjustment unit 28 for a setting to a fixed or parameterized distance, the respective current distance from an object or code scanned by the reading beam 16 is preferably measured. This can be done by an additional distance measuring unit, not shown.

[0026] The laser beam 16 itself, however, is preferably used for a distance measurement in that, for example, a frequency is imparted onto the laser beam 16 by amplitude modulation and the distance is determined in a phase method from the phase offset between the transmission time and the reception time.

[0027] The focus adjustment unit 28 is shown schematically in FIG. 1 and again in a preferred embodiment in a three-dimensional view in accordance with FIG. 2. The same reference numerals respectively designate the same features or mutually corresponding features.

[0028] The focus adjustment unit 28 has a pivot arm 30 that holds the transmission optics 14 and that is supported at one end at the code reader 10 via a leaf spring 32, for example. Movements of the pivot arm 30 with respect to the leaf spring 32 forming a support point or pivot point therefore provide a difference distance between the transmission optics 14 and the light transmitter 12 and thus a focus adjustment. Such a movement is effected by a moving coil unit 34 that has a permanent magnet 36 in a fixed position with respect to the code reader 10 and has a coil 38 through which current flows, which dips into its magnetic field and which is attached to an end of the pivot arm disposed opposite the leaf spring 32.

[0029] The respective degree of the pivot movement or deflection of the pivot arm 30 can be controlled by the evaluation unit 26 by a current flow through the coil 38. A focus table is, for example, stored for this purpose that links the required controls to measured distances or focal positions to be set that are fixed in another manner. The transmission ratio between movements at the moving coil unit 34 and movements of the transmission optics 14 is known and is fixed by the geometry of the pivot arm 30, of the arrangement of the transmission optics on the pivot arm 30 and of the support of the pivot arm 30, that is the pivot point at the leaf spring 32 here and the point of engagement of the adjustment force at the coil 38. The focal resolution can thereby be set.

[0030] The focus adjustment explained at the transmission side in a code scanner can in principle also be used at the reception side or in a camera-based code reader instead of in a code scanner.

[0031] FIG. 3 again shows the moving coil unit 34 with a magnetic field indicated by arrows and the coil 38 immersed therein. The permanent magnet 36 preferably has two magnet pairs 36a-b and 36c-d that respectively generate a homogeneous magnetic field between them and in which a respective half 38a-b of the coil 38 is located. The upper magnet pair 36a-b and the lower magnet pair 36c-d are oppositely polarized in this respect, with this being simply achievable by a converse arrangement. For the current in the upper half 38a of the coil 38 flows in the converse direction than in the lower half 38b due to the windings and the arrangement. It is achieved by the different polarization of the magnet pairs 36a-b, 36c-d that the Lorentz force is directed the same on both halves 38a-b of the coil 38. Both magnet pairs 36a-b, 36c-d are each connected by a reflux 40a-b to close the magnetic circuit.