DEVICE AND METHOD FOR MEASURING AN OBJECT

Abstract

The invention relates to a device and to a method for measuring an object that moves in a direction of movement along a movement axis, wherein the device has a first sensor arrangement having a first SMI sensor and a second SMI sensor, wherein the SMI sensors irradiate measurement light beams in opposite directions along a movement axis. A control and evaluation unit is configured to receive first and second measured signals, to determine a speed of the object along the movement axis from at least one of the measured signals, to detect a first characteristic change of the second measured signal, a first characteristic change of the first measured signal, and a second characteristic change of the first measured signal, and to determine an object length of the object along the movement axis.

Claims

1. A device for measuring an object that moves in a direction of movement along a movement axis, the device comprising a first sensor arrangement having a first self-mixing interference sensor (SMI sensor) for transmitting first measurement light beams along a first measurement axis, for receiving first measurement light beams reflected back from a first working zone of the first SMI sensor, and for generating a first measured signal from the first measurement light beams reflected back, wherein the first SMI sensor is oriented in such a way that the transmitted first measurement light beams run at least in part in the direction of movement of the object, a second SMI sensor for transmitting second measurement light beams along a second measurement axis, for receiving second measurement light beams reflected back from a second working zone of the second SMI sensor, and for generating a second measured signal from the second measurement light beams reflected back, wherein the second SMI sensor is oriented in such a way that the transmitted second measurement light beams run at least in part against the direction of movement of the object, wherein the first working zone has an end remote from the first SMI sensor and the second working zone has an end remote from the second SMI sensor 18.2, and the ends define a measurement distance having a measurement distance length in parallel with the movement axis; a control and evaluation unit for receiving the first measured signal and the second measured signal and for determining a speed of the object along the movement axis from at least one of the measured signals, wherein the control and evaluation unit is configured to detect a first characteristic change of the second measured signal at a first time; to detect a first characteristic change of the first measured signal at a second time; to detect a second characteristic change of the first measured signal at a third time; And to determine an object length of the object along the movement axis while using the first time, the third time, the speed, and the measurement distance length.

2. The device in accordance with claim 1, wherein the control and evaluation unit is configured to store the speed over the time.

3. The device in accordance with claim 1, wherein the control and evaluation unit is configured to determine a length value at a constant speed of the object from a time difference between the third time and the first time and the constant speed and to determine the length of the object along the movement axis from the length value and the measurement distance length.

4. The device in accordance with claim 2, wherein the control and evaluation unit is configured to determine a length value at a variable speed by temporal integration of the variable speeds between the first time and the third time and to determine the length of the object along the movement axis from the length value and the measurement distance length.

5. The device in accordance with claim 3, wherein the measurement distance length is positive when the end of the first working zone remote from the first SMI sensor is arranged upstream of the end of the second working zone remote from the second SMI sensor in the direction of movement, is negative when the end of the first working zone remote from the first sensor is arranged downstream of the end of the second working zone remote from the second SMI sensor in the direction of movement, and the control and evaluation unit is configured to determine the length of the object by addition of the length value and the measurement distance length.

6. The device in accordance with claim 4, wherein the measurement distance length is positive when the end of the first working zone remote from the first SMI sensor is arranged upstream of the end of the second working zone remote from the second SMI sensor in the direction of movement, is negative when the end of the first working zone remote from the first sensor is arranged downstream of the end of the second working zone remote from the second SMI sensor in the direction of movement, and the control and evaluation unit is configured to determine the length of the object by addition of the length value and the measurement distance length.

7. The device in accordance with claim 1, wherein the first measurement axis has a first angle with respect to a plane perpendicular to the movement axis and the second measurement axis has a second angle with respect to the plane perpendicular to the movement axis, with the angles having different signs and with the amounts of the angles being the same.

8. The device in accordance with claim 1, wherein the first measurement axis and the second measurement axis lie in a common measurement plane.

9. The device in accordance with claim 8, wherein the movement axis of the object lies in the common measurement plane.

10. The device in accordance with claim 1, wherein the first measurement axis and the second measurement axis lie in parallel measurement planes.

11. The device in accordance with claim 10, wherein the movement axis of the object lies between the parallel measurement planes.

12. The device in accordance with claim 1, wherein the object is moved by a transport medium, with the transport medium being disposed in at least one working zone of the SMI sensors.

13. The device in accordance with claim 1, wherein the object is moved by a transport medium, with the transport medium being disposed outside the working zones of the SMI sensors.

14. The device in accordance with claim 1, wherein the control and evaluation unit is configured to determine the speed along the movement axis while using the first and second measured signals.

15. The device in accordance with claim 1, wherein the device has a second sensor arrangement having a third SMI sensor and a fourth SMI sensor, with the measurement axes of the third and fourth SMI sensors being aligned in parallel with the measurement axes of the first and second SMI sensors of the first sensor arrangement.

16. A method of measuring an object that moves in a direction of movement along a movement axis, the method comprising the steps of: transmitting first measurement light beams by a first self-mixing interference sensor (SMI sensor) of a first sensor arrangement along a first measurement axis, wherein the first SMI sensor is oriented in such a way that the transmitted first measurement light beams extend at least in part in the direction of movement of the object; receiving first measurement light beams reflected from a first working zone of the first SMI sensor; generating a first measured signal from the reflected first measurement light beams; transmitting second measurement light beams by a second self-mixing interference sensor of the first sensor arrangement along a second measurement axis, wherein the second SMI sensor is oriented in such a way that the transmitted second measurement light beams extend at least in part against the direction of movement of the object; receiving second measurement light beams reflected from a second working zone of the second SMI sensor; generating a second measured signal from the reflected second measurement light beams; wherein the first working zone has an end remote from the first SMI sensor and the second working zone has an end remote from the second SMI sensor and the ends define a measurement distance having a measurement distance length in parallel with the movement axis; receiving the first measured signal and the second measured signal by a control and evaluation unit; and determining a speed along the movement axis from at least one of the measured signals, detecting a first characteristic change of the second measured signal at a first time; detecting a first characteristic change of the first measured signal at a second time; detecting a second characteristic change of the first measured signal at a third time; and determining a length of the object along the movement axis while using the first time, the third time, the speed, and the measurement distance length.

Description

[0034] The invention will be explained in detail in the following with reference to embodiments and to the drawings. The same parts in the drawings are provided with the same reference numerals here. There are shown in the drawings:

[0035] FIG. 1 a device in accordance with the invention for measuring an object moving along a movement axis;

[0036] FIG. 2 an exemplary scanning of an object by a device in accordance with the invention at different times with a transport medium disposed outside the working zones of the SMI sensors;

[0037] FIG. 3 a scanning of an object by a device in accordance with the invention at different times with a transport medium disposed within the working zones of the SMI sensors; and

[0038] FIG. 4 a device in accordance with the invention for measuring an object moving along a movement axis using two sensor arrangements arranged in parallel.

[0039] FIG. 1 shows a device 10 in accordance with the invention for measuring an object 14 moving at a speed v along a movement axis 12 in a direction of movement 13. The device 10 comprises a first sensor arrangement 16 having a first self-mixing interference sensor (SMI sensor) 18.1 and a second SMI sensor 18.2 as well as a control and evaluation device 20 for controlling the SMI sensors 18.1, 18.2 and for receiving and/or evaluating measured signals 44, 48 of the SMI sensors 18.1, 18.2. The control and evaluation device 20 has an interface 21 for forwarding the measured signals and/or evaluation results. The interface 21 can also be configured to receive control signals of a higher ranking control. The first SMI sensor 18.1 transmits measurement light beams from an aperture 36.1 along a first measurement axis 22.1 that has a first angle α.sub.1 with respect to a plane 24 perpendicular to the movement axis 12. The second SMI sensor 18.2 transmits measurement light from an aperture 36.2 along a second measurement axis 22.2 that has a second angle α.sub.2 with respect to a plane 24 perpendicular to the movement axis 12. The angles α.sub.1, α.sub.2 are directed angles having an orientation that is specified via a sign before the amount of the angle. In the embodiment, the angles have the same amount; α.sub.2=−α.sub.1 applies. The measurement axes 22.1, 22.2 can furthermore lie in a common measurement plane; the plane of the drawing in the embodiment. If, as in the embodiment, the movement axis 12 lies in or in parallel with the measurement plane, the speed v of the object 14 results from the speeds v.sub.Sensor1, v.sub.Sensor2 determined by the SMI sensors 18.1, 18.2 in accordance with the formulas

v=v.sub.Sensor.sub.1 cos(90−α.sub.1)

or

v=v.sub.Sensor.sub.2 cos(90−α.sub.2)

[0040] The first SM! sensor 18.1 and the second SMI sensor 18.2 each have a first working zone 26.1 and a second working zone 26.2 along the measurement axes 22.1, 22.2, with only measurement light beams reflected back from the working zones 26.1, 26.2 generating measured signals 44, 48 that are supplied to further processing. The end 28.1 of the first working zone 26.1 remote from the first SMI sensor 18.1 and the end 28.2 of the second working zone 18.2 remote from the second SMI sensor 18.2 define a measurement distance in parallel with the movement axis 12 of the object 14 having a measurement distance length I.sub.M. Since, in the embodiment, the end 28.1 of the first working zone 26.1 remote from the first SMI sensor 18.1 is disposed downstream of the end 28.2 of the second working zone 26.2 remote from the second SMI sensor 18.2 in the direction of movement 13 of the object 14, the measurement distance length I.sub.M enters into a determination of the object length l.sub.Obj with a negative amount.

[0041] The first sensor arrangement 16 is arranged at a height h.sub.Sensor measured from the apertures 36.1, 36.2 of the SMI sensors 18.1, 18.2 above a transport medium 34 on or with which the object 14. moves. In the embodiment, the ends 28.1, 28.2 of the working zones 26.1, 26.2 remote from the SMI sensors 18.1, 18.2 lie at a distance h.sub.offset above the transport medium 34 so that the transport medium 34 is not detected by the SMI sensors 18.1, 18.2. The vertical distance 38 of the apertures 36.1, 36.2 of the SMI sensors 18.1, 18.2 from the point of intersection of the measurement axes 22.1, 22.2 is called the standoff distance (SD).

[0042] FIG. 2 schematically shows a first example of the functional principle of the device in accordance with the invention. The sensor arrangement 16 is arranged at a first height h.sub.Sensor1 above the transport medium 34, for example a conveyor belt, such that the transport medium 34 is not disposed in the working zones 26.1, 26.2 of the SMI sensors 18.1, 18.2. The transport medium 34 thereby does not generate any intensity signal in the SMI sensors 18.1, 18.2, as shown in the intensity-time diagram 40 in the lower left corner of FIG. 2. The SMI sensors 18.1, 18.2 of the sensor unit 16 thus also do not deliver any speed signals, as shown in the lower right corner in the speed-time diagram 42 of FIG. 2.

[0043] At a first time T.sub.1, the object 14 that moves along the movement axis 12 on the transport medium 34 enters into the second measurement axis 22.2 of the second SMI sensor 18.2. Measurement light beams that were transmitted by the second SMI sensor 18.2 are reflected from the object 14, move at least in part along the second measurement axis 22.2 back to the second SMI sensor 18.2, and there generate a second measured signal 44 with an intensity I (dashed line in the intensity-time diagram 40). At the time T.sub.1, a first characteristic change of the second measured signal 44 therefore takes place, namely an abrupt change of the intensity from a value below a detection level to a value at which the second SMI sensor 18.2 can determine a speed v so that the speed-time diagram 42 also shows a second sped signal 46 differing from zero (dashed line in the speed-time diagram 42) from the time T.sub.1 onward.

[0044] Measurement light beams also transmitted by the first SMI sensor 18.1 at a second time T.sub.2 are reflected from the object 14, move at least in part along the first measurement axis 22.1 back to the first SMI sensor 18.2 and there here generate a second measured signal 48 with an intensity I (dashed line in the intensity-time diagram 40). At the time T.sub.2 a first characteristic change of the first measured signal 48 therefore takes place analog to the change of the second measured signal 44 at the time T.sub.1. Accordingly, the first SMI sensor 18.1 now also delivers a second speed signal 50 differing from zero (chain-dotted line in the speed-time diagram 42).

[0045] At a third time T.sub.3, the object 14 exits the first measurement axis 22.1 of the first SMI sensor 18.1. A second characteristic change of the first measured signal 48 thus takes place whose intensity likewise again falls to a value below the detection level so that a first speed signal 50 is also no longer present.

[0046] At a constant object speed v.sub.const, the object length l.sub.Obj results from geometrical considerations as

l.sub.Obj=(T.sub.3−T.sub.1).Math.v.sub.const+l.sub.M

where l.sub.M designates the measurement distance length of the sensor arrangement 16. Since, in the embodiment, the end 28.1 of the first working zone 26.1 remote from the first SMI sensor 18.1 is disposed downstream of the end 28.1 of the second working zone 26.2 remote from the second SMI sensor 18.2 in the direction of movement 13 of the object 14, the measurement distance length I.sub.M enters into a determination of the object length l.sub.Obj with a negative amount, that is it is deducted from the length that results from the difference of the times T.sub.3 and T.sub.1.

[0047] At a variable object speed v.sub.var, the object length l.sub.Obj can be determined using a time-dependent variable object speed v.sub.var(t) stored over the time in the SMI sensors 18.1, 18.2 or in the evaluation unit 20:

l.sub.Obj=∫.sub.T.sub.1.sup.T.sup.3v.sub.var(t)dt+l.sub.M

then applies.

[0048] FIG. 3 schematically shows a second example of the functional principle of the device in accordance with the invention. The sensor arrangement 16 is arranged at a second height h.sub.Sensor2 above the transport medium 34 such that the transport medium 34 is disposed in the working zones 26.1, 26.2 of the SMI sensors 18.1, 18.2. The transport medium 34 thereby generates intensity signal 64, 68, as shown in the intensity-time diagram 60 in the lower left corner of FIG. 3. The SMI sensors 18.1, 18.2 of the sensor unit 16 thus also deliver speed signals, as shown in the speed-time diagram 62 in the lower right corner of FIG. 3.

[0049] At a first time T.sub.1, the object 14 that moves along the movement axis 12 on the transport medium 34 in a direction of movement 13 enters into the second measurement axis 22.2 of the second SMI sensor 18.2. Measurement light beams that were transmitted from the second SMI sensor 18.2 are reflected from the object 14 move at least in part along the second measurement axis 22.2 back to the second SMI sensor 18.2. Due to a different reflectivity of the transport medium 34 and the object 14 (a higher reflectivity of the object 14 in comparison with the transport medium 34 in the example), the intensity of the second measured signal 64 changes (dashed line in the intensity-time diagram 60). At the time T.sub.1, a first characteristic change of the second measured signal 64 therefore takes place, namely an abrupt increase of the intensity that can be sensed by the second SMI sensor 18.2. Since the object 14 moves at the same speed v as the transport medium 34, the speed v determined by the second SMI sensor 18.2 and the corresponding first speed signal 66 (dashed line in the speed-time diagram 62) do not change.

[0050] At a second time T.sub.2, measurement light beams transmitted by the first SMI sensor 18.1 are also reflected from the object 14 and move at least in part along the first measurement axis 22.1 back to the first SMI sensor 18.1. Due to different reflectivity of the transport medium 34 and the object 14, the intensity of the first measured signal 68 (chain-dotted line in the intensity-time diagram 60) also does not change here. At the time T.sub.2, a first characteristic change of the first measured signal 68 therefore takes place, namely an abrupt increase of the intensity that can be sensed by the first SMI sensor 18.1. Since the object 14 moves at the same speed v as the transport medium 34, the speed determined by the first SMI sensor 18.1 and the corresponding first speed signal 70 (chain-dotted line in the speed-time diagram 62) also do not change.

[0051] At a third time T.sub.3, the object 14 exits the first measurement axis 22.1 of the first SMI sensor 18.1. A second characteristic change of the first measured signal 68 thus takes place whose intensity again drops to the value before the second time T.sub.2.

[0052] In the example described in FIG. 3, it is therefore possible to also determine the speed of the transport medium in addition to the object speed v. For the length determination, however, a sufficient difference of the reflectivity of the transport medium 34 and of the object 14 to be measured is necessary so that a characteristic change of the intensity of the measured signal can be sensed by the SMI sensors 18.1, 18.2 and the times T.sub.1 to T.sub.3 can thus be reliably determined. The length determination of the object 14 takes place as in the exampled described in FIG. 2.

[0053] FIG. 4 shows a schematic representation of a plan view of a further embodiment of a device 80 in accordance with the invention that has a first sensor arrangement 16 and a second sensor arrangement 16b as described in FIG. 1. The second sensor arrangement 16b can be designed like the first sensor arrangement 16, with the measurement axes of the SMI sensors of the first and second sensor arrangements 16, 16b being oriented such that the measurement axes lie in parallel measurement planes 88a, 88b.

[0054] If rectangular objects 84, 89 move on a first transport medium 81 along a movement axis 82 (for example packages on a conveyor belt) through the working zones of the sensor arrangements 16, 16b, the orientation of the objects 84, 94 on the transport medium 81 can be determined by determining the object lengths L.sub.1a, L.sub.1b, L.sub.2a, L.sub.2b and the entry of the objects into the working zones or the exiting of the objects from the working zones of the SMI sensors of the sensor arrangements 16, 16b, that is by a comparison of time developments of characteristic signal changes.

[0055] If, for example as with the first object 84, the side surfaces of the first object are aligned in parallel with or perpendicular to the measurement planes 88a, 88b of the sensor arrangements 16, 16b, they determine, on the one hand, identical lengths L.sub.1a, L.sub.1b, L.sub.2a, L.sub.2b of the first object 84 and, on the other hand, the first object 84 will simultaneously enter, within the framework of customary tolerances, the working zones of the SMI sensors of the sensor arrangements 16, 16b.

[0056] If, as with the second object 94, the side surfaces are not aligned in parallel with the measurement planes 88a, 88b of the sensor arrangements 86a, 86b, the second object 94 will, on the one hand, enter into the working zones of the SMI sensors of the sensor arrangements 86a, 86b at different times; on the other hand, the determined lengths L.sub.2a, L.sub.2b of the second object 94 will differ.

[0057] If the dimensions of the object are known, the location of the objects 94 on the transport medium 81 can thus be determined.