阅读说明：本技术 用于确定传送机上物体位置的方法和装置 (Method and device for determining the position of an object on a conveyor ) 是由 马克·西普里亚尼 米歇尔·帕格利亚 埃里克·奥索 于 2019-12-12 设计创作，主要内容包括：本发明提供了一种用于确定在传送线(1)的支撑平面上线性前进的物体(2)的位置的装置,所述装置包括：用于确定在所述支撑平面上的物体(2)的位置的第一和第二光束(220、230)的光源(22A、23A),其产生具有大致点状横截面尺寸的准直光束(220、230),所述光束(220、230)沿着定义与所述支撑面平行的平面并与前进方向(F)形成锐角的路径传播；以及分别用于检测第一和第二光束(220、230)的检测器(22B、23B)。处理单元(12)包括用于比较物体通过每一光束(220、230)的时刻的装置,以及基于该比较结果,检测物体(2)的位置相对于参考位置的可能偏移。(The invention provides a device for determining the position of an object (2) advancing linearly on a support plane of a conveyor line (1), said device comprising: -a light source (22A, 23A) of first and second light beams (220, 230) for determining the position of an object (2) on said support plane, which generates a collimated light beam (220, 230) having a substantially punctiform cross-sectional dimension, said light beams (220, 230) propagating along a path defining a plane parallel to said support plane and forming an acute angle with the advancement direction (F); and detectors (22B, 23B) for detecting the first and second light beams (220, 230), respectively. The processing unit (12) comprises means for comparing the instants at which the object passes through each beam (220, 230), and, on the basis of the comparison, detecting a possible offset of the position of the object (2) with respect to a reference position.)

1. Method for determining objects (2) advancing linearly on a support plane of a conveyor line (1), wherein the position of said objects (2) on said support plane, in particular the position of the same objects in a direction (y) transverse to the advancing direction (F), is determined by detecting them by means of first and second light beams (220, 230) intersecting each other, characterized in that: the light beams (220, 230) are collimated light beams having a substantially punctiform cross-sectional dimension, which propagate along paths defining a plane parallel to the support plane and forming an acute angle with the advancement direction (F), and a possible displacement of the object (2) with respect to a reference position is detected by comparing the instants at which the object passes through each light beam (220, 230).

2. The method of claim 1, wherein:

detecting the moment at which the object (2) enters the first and second beams (220, 230) or the moment at which the object (2) leaves the first and second beams (220, 230), and, if any, deriving a range of offsets from the time difference between the moment at which the object enters each beam (220, 230) and the moment at which the object leaves each beam (220, 230); or

-detecting the moment at which the object (2) enters the first and second beams (220, 230) and the moment at which the object (2) leaves the first and second beams (220, 230), and-deriving the range of offset, if any, from a combination of the time difference between the moments of entering each beam (220, 230) and the moments of leaving each beam (220, 230).

3. The method according to claim 1 or 2, characterized in that: the first and second light beams (220, 230) form the same angle with the advancing direction (F) of the object (2).

4. A method according to any one of claims 1-3, characterized in that: the position of the object (2) in a direction (z) perpendicular to the support plane is also determined by:

detecting the passage of the object (2) by means of a third light beam (210), which is a planar light beam lying in a plane perpendicular to the support plane, which is parallel to the support plane and propagates transversely to the advancement direction (F), and which is set with respect to the support plane at a height at which it can be intercepted by the top of the object (2); and

determining the extent to which the third light beam (210) is intercepted by the object (2);

and detecting a possible displacement of the object (2) with respect to a reference position by comparing the extent of the portion of the third light beam (210) intercepted by the detected object with the extent of the portion intercepted by the object located at the reference position.

5. The method according to any one of claims 1-4, wherein: further comprising the step of preliminary alignment of the light beam (210, 220, 230) with respect to the advancing direction, by using an optical pointer (31) and a target (32), one of which is temporarily associated with the position detection unit (11) and the other with the conveying line (1).

6. Device for determining the position of objects (2) advancing linearly on a support plane of a conveyor line (1), comprising:

a unit (11) for determining the position of the object (2) on the support plane, in particular the position in a direction (y) transverse to the advancement direction, said unit comprising a light source (22A, 23A) of a first and a second light beam (220, 230) and means (22B, 23B) for detecting the light beams (220, 230), arranged to detect the passage of the object through the same light beams; and

a unit (12) for processing a signal resulting from said detection;

the device is characterized in that:

-said light source (22A, 23A) generates a collimated light beam (220, 230) having a substantially punctiform cross-sectional dimension, which propagates along a path defining a plane parallel to said support plane and forming an acute angle with said advancing direction (F);

said beam detection means (22B, 23B) comprising a first and a second detector (22B, 23B) for detecting a first and a second light beam (220, 230), respectively; and

the processing unit (12) comprises means for comparing the instants at which the object passes each light beam (220, 230) and, based on the comparison, detecting a possible offset of the position of the object (2) with respect to a reference position.

7. The apparatus of claim 6, wherein: the comparison means is arranged to detect a possible offset relative to the reference position by comparing:

the moment when the object (2) enters the first and second light beams (220, 230) or the moment when the object (2) leaves the first and second light beams (220, 230); or

The moment when the object (2) enters the first and second light beams (220, 230) and the moment when the object (2) leaves the first and second light beams (220, 230);

and determining the extent of the offset, if any, from the time difference between the compared times, or from a combination of the time difference between the times at which the object (2) enters the first and second beams (220, 230) and the time difference between the times at which the object (2) leaves the first and second beams (220, 230), respectively.

8. The apparatus of claim 6 or 7, wherein: the light sources (22A, 23A) of the first and second light beams (220, 230) are arranged so that the paths of the light beams form the same angle with the direction of advance (F) of the object (2).

9. The apparatus according to any one of claims 6-8, wherein: the unit (11) for determining the position of the object (2) further comprises a unit for determining the position of the object (2) in a direction (z) perpendicular to the support plane:

a light source (21A) of a third light beam (210) generating a planar light beam lying in a plane perpendicular to said support plane and propagating parallel to said support plane and transversal to said advancement direction (F), said light source (21A) being arranged with respect to said support plane at a height such that said third light beam (210) is intercepted by the top of said object (2); and

a detector (21B) of said third light beam (210) connected to a processing unit (12);

wherein the processing unit (12) is arranged to determine the extent of the portion of the third light beam (210) intercepted by the object (2), and the comparison means is arranged to detect a possible shift of the position of the object (2) with respect to a reference position by comparing the extent of the portion of the third light beam (210) intercepted by the detected object with the extent of the portion intercepted by the object located at the reference position.

10. Apparatus for conveying objects (2) which are linear on a support plane of a conveyor line (1) and which are arranged towards means (3, 4) for handling the objects, wherein the apparatus comprises a device according to any one of claims 6-9 for determining the position of the objects (2) on the support plane, in particular the position in a direction (y) transverse to an advancing direction (F), and the possible positions of the objects (2) in a direction (z) perpendicular to the support plane; detecting a possible offset of the position of the object (2) with respect to an optimal reference position for the operation; and, in the event of an offset, providing the handling device (3, 4) with a signal for correcting its position.

Technical Field

The invention relates to a method and a device for determining the position of objects conveyed on a conveyor line, in particular on a conveyor line moving at high speed. Preferably, but not exclusively, the invention applies to the field of packaging of objects, and in the most preferred application, the objects are bottles conveyed on a conveyor of a bottling plant towards an operating robot.

For clarity and simplicity of description, reference will be made primarily hereinafter to this most preferred application.

Background

In the field of packaging of articles, such devices are very common: the articles to be packaged are arranged in a row along a conveyor line comprising one or more conveyors moving through a series of work stations, wherein said objects are submitted to the different operations required for their packaging.

For example, in a bottling plant, the conveyor passes through a series of work stations, including, for example, filling stations, capping stations, labeling stations, etc. In certain work stations, where objects are to be removed from a conveyor for performing a prescribed operation, in highly automated systems, robots, such as humanoid robots, are commonly used for this purpose.

In order for the bottles to be able to be gripped by the robot, their position in three directions must fall within a rather narrow tolerance range, for example, ± 2 mm. However, the bottles may have different heights (e.g., due to some of the bottles not having caps, or caps not being fully inserted or screwed, etc.), and the unevenness of the bottoms of the bottles and the movement of the bottles on the conveyor may result in misalignment of the bottles. Furthermore, the bottles may not follow each other at regular steps due to irregularities in the advancement of the conveyor. All these irregularities easily exceed the specified tolerance limits, so that, in order to achieve good productivity of the device, the device is equipped with means for correcting the relative position of the robot and the bottles and ensuring that the robot can pick up all or almost all the bottles operating on the workstation.

Many systems are known in the art that are capable of detecting the position of an object conveyed on a conveyor.

The most common systems utilize vision systems, such as high speed cameras. Supplementing a production line with a vision system forces a number of problems to be solved in relation to object lighting, calibration of the vision system, detection accuracy, etc. Furthermore, in the case of high speed production lines, such as those to which the present invention is concerned, it is difficult in such systems to meet the strict constraints imposed by the line on the camera shooting speed, illumination time and response time of the correction system (which must typically be <20 ms). Furthermore, the vision system is expensive.

Other systems are based on detecting the passage of an object in front of one or more light sources.

US4,105,925 discloses a system comprising two light sources that send diverging planar light beams to a conveyor that intersect at a single transverse line of the conveyor. The diode array detects the light of the line. An object passing through the line intercepts the beam of light, thereby forming a light ray on the object at a position before or after the intersection line. Thus, the diode array only detects line segments that exceed the boundary of the object, thereby enabling the shape and orientation of the object to be determined. The system provides information to the robot arm including the coordinates x, y (mean, maximum and minimum coordinates) of the object to perform the object operation.

The above-described system of providing a light source for sending a light beam onto a conveyor entails the problem of requiring the selection and/or correction of parameters according to different conveyor types.

US4,494,656 discloses a device for detecting objects (bottles) moving on a conveyor. The apparatus includes an optical sensor (including, for example, a laser) for detecting the presence of an object at a height near the surface of the conveyor. The device detects the time interval between successive transitions (rising/falling edges) of the output signal of the light sensor, compares this time with a threshold value, and based on this comparison, detects a stuck or falling object to be removed.

The above-described system cannot determine the exact position of the object on the conveyor, but only whether the object is stuck or dropped.

Disclosure of Invention

A first object of the present invention is to overcome the drawbacks of the prior art by providing a system for determining the position of objects conveyed on a conveyor line.

Another object of the invention is to provide a system for determining the position of an object transported on a transport line towards a handling robot, with a better reliability and a higher flexibility in the robot handling.

The above and other objects are achieved by the method and device as claimed in the appended claims.

In the method of the invention, the position of the object on the support plane, in particular in a direction transverse to the advance direction, is determined by detecting the passage of the object through the first and second light beams which intersect one another. The light beam is a collimated light beam having a substantially punctiform cross-sectional dimension, which propagates along a path defining a plane parallel to the supporting object and forming an acute angle with the advancing direction. By comparing the time instants at which the object passes through each beam, a possible shift in the position of the object relative to a reference position can be detected.

Advantageously, the position of the object in a direction perpendicular to the support plane is also determined. To this end, the object is detected by a third light beam, which is a planar light beam lying in a plane perpendicular to the support plane, which is parallel to the support plane and propagates transversely to the advancement direction and is arranged with respect to said support plane at a height at which it can be intercepted by the top of said object, and the vertical extent of the portion of said third light beam intercepted by the object is determined. Detecting a possible shift of the position of the object with respect to a reference position by comparing the vertical portion of the third light beam intercepted by the detected object with the vertical portion intercepted by the object located at the reference position.

An apparatus for implementing the method, comprising:

a unit for determining the position of an object on a support plane, in particular in a direction transverse to the advancement direction, the unit comprising a pair of sources of a first and a second light beam, which form a collimated light beam having a substantially punctiform cross-sectional dimension, which propagates along a path defining a plane parallel to the support plane and forming an acute angle with the advancement direction; and a pair of detectors for detecting the first and second light beams, respectively; and

a unit for detecting and correcting possible shifts in the position of the object relative to a reference position, the unit being arranged to compare the instants at which the object passes through each beam and to detect a possible shift based on the result of the comparison.

Advantageously, the device further comprises a unit for determining the position of the object in a direction perpendicular to the support plane, comprising:

a source of a third light beam, which generates a planar light beam lying in a plane perpendicular to the support plane, parallel to said support plane and propagating transversely to the advancement direction, said source being arranged at a height with respect to said support plane such that said third light beam is intercepted by the top of said object; and

a receiver of said third light beam connected to a unit for detecting and correcting possible offsets;

and the means for detecting and correcting the offset are arranged to determine the vertical extent of the portion of the third light beam intercepted by the object, and to detect the offset by comparing the vertical extent of the portion of the third light beam intercepted by the detected object with the vertical extent of the portion intercepted by the object located at the reference position.

The invention also relates to a device for conveying objects aligned on a support plane towards means for handling them, comprising means of the invention for: determining the position of the object on the support plane, in particular in a direction transverse to the advancing direction and possibly perpendicular to the support plane; detecting a possible offset of the position of the object with respect to a reference position for optimal operation; and, in the case of an offset, providing the operating device with a signal for correcting its position.

The offset is determined and corrected with the sensitivity, speed and accuracy required for high speed production lines using laser sensors, in particular a pair of laser photocells for determining the position of the object on the support plane, and a laser sheet sensor for determining the position on the vertical plane by detecting the passage of the object through the sensor beam. This can improve the reliability of the robot operation and improve the gripping tolerance, since the invention can also correct for deviations that fall within the tolerance range. Furthermore, laser-based systems are simpler and faster to install than vision systems.

Drawings

The above and other features of the invention will become more apparent from the following description of a preferred embodiment, given by way of non-limiting example, with reference to the accompanying drawings, in which:

fig. 1 shows a basic solution for operating a robot device for transferring bottles by a conveyor, said robot device being equipped with the apparatus of the invention;

FIG. 2 shows a schematic plan view of a part of an apparatus comprising the device of the invention;

FIG. 3 shows a perspective view of the portion of the apparatus shown in FIG. 2;

FIG. 4 shows a basic scheme of an initial alignment system for the apparatus of the present invention;

FIG. 5 shows a basic schematic of vertical correction;

FIG. 6 shows signals for vertical correction;

FIGS. 7 and 8 show schematic diagrams of lateral correction;

FIG. 9 shows signals for lateral correction; and

fig. 10 shows a similar graph to fig. 7 and 8, showing the independence of the lateral correction from the object diameter.

Detailed Description

With reference to fig. 1, reference numeral 1 denotes a conveyor advancing in the direction indicated by the arrow F and conveying a series of objects 2, in the example considered as bottles, towards a handling robot 3 having a gripping head 4 for gripping the bottles 2. The conveyor 1 is a high-speed conveyor, typically moving at 100m/min, and it is associated, on part of its path, with guides 5, said guides 5 serving to hold the bottles in position and to stabilize the bottles 2 as the bottles 2 advance. The dotted line a-a indicates the longitudinal axis of the conveyor 1. The robot 3 picks up the bottles 2, for example from the conveyor 1, inserts at the bottle position a bottle to be taken to a station downstream of the conveyor, and takes the picked-up bottle to a position outside the conveyor 1 according to the trajectory T. The robot 3 is, for example, an anthropomorphic robot moving in three orthogonal directions x (longitudinal coordinate parallel to the advancement direction F), y (transverse coordinate of the direction x perpendicular to the plane of the conveyor) and z (vertical coordinate perpendicular to the plane x of the conveyor). The robot 3 operates in an intervention zone, which is located downstream of the guide 5 and which is initially set by a device 6, for example a photocell arrangement (see figures 2, 3), said device 6 detecting the passage of the bottle 2 and thus activating the same robot.

In order for the bottles 2 to be gripped by the gripper head 4 of the robot 3, their position in the three directions x, y, z must fall within a predetermined and rather limited tolerance range (e.g. ± 2 mm). According to the invention, in order to correct the vertical and horizontal offset of the bottle 2 with respect to a reference position, which is an optimal position for the robot 2 to grasp the bottle 2, a device 10 (hereinafter referred to as correction device) is provided upstream of the actuation device 6. The device detects the position of the bottle 2 in three directions x, y, z, determines a possible offset from a reference position and, if necessary, commands the robot 3 to move to compensate for this offset. The device 10 is located substantially at the end of the guide 5, upstream of the actuating device 6. The distance between the device 10 and the actuating device 6 must be large enough to take the position of the bottle 2 and calculate and send to the robot the corrections, if any, before the robot grasps the bottle 2, and, at the same time, short enough to ensure the validity of the calculated corrections. For example, the device 10 must provide the correction signal with a delay time shorter than a few tens of milliseconds, typically shorter than 20 ms.

The correction device 10 comprises a unit 11 for determining the position of the bottle 2 and a unit 12 for determining possible offsets with respect to a reference position and corrections to be transferred to the robot 3. The unit 11 in turn comprises two separate and independent parts, respectively determining the vertical position (coordinate z) and the horizontal position of the bottle, in particular in the transverse direction (coordinate y).

With reference to fig. 2 and 3, the means for determining the coordinate z consist of a laser sheet sensor 21, which laser sheet sensor 21 comprises a light source 21A and a detector 21B and emits a planar light beam (sheet) 210 extending in a plane perpendicular to the support plane, for example in the vertical plane z-y, and propagating in a direction y parallel to the support plane. The sensor 21 is arranged at a distance from the surface of the conveyor 1 such that the light beam 210 is intercepted by the bottles 2 substantially at the top of their caps. Given a certain type of bottle, the position and extension of the laser patch 210 in the plane z-y must be such that the patch can in any case also be intercepted by bottles having a height lower than the nominal height (for example uncapped bottles). Preferably also partly intercepted by bottles having a height above the nominal height (for example bottles with broken caps or with wrong insertion). The determination and correction of the position is determined based on the vertical extent of the portion intercepted by the sheet 210 and therefore on the processing of the output signal of the sensor 21, as will be explained in more detail below. The output signal of the sensor 21 will be sampled at a sufficiently high sampling rate so as to provide a minimum number of samples for a given bottle to compensate for shape aberrations. For example, a 1ms sample time would meet this requirement in view of the conveyor speed described above.

The means for determining the coordinate y consist of two high-speed laser photocells 22, 23, the laser beams 220, 230 of which travel in a plane parallel to the plane x-y, with paths at an acute angle to the direction of advance of the conveyor belt 1 and therefore with respect to the axis a-a. Reference numerals 22A, 23A and 22B, 23B denote the source and detector of the photocells 22, 23, respectively. Also, the plane defined by the beams 220, 230 may be located in a position corresponding to an area of the bottle cap, but this is not essential. Advantageously, the two light beams 220, 230 are arranged at the same angle with respect to the axis a-a, so that their projections on the propagation plane corresponding to this axis cross each other. Preferably, the angle is 45 °: this angle has been shown to have the best resolution sensitivity and to minimize overall size.

The coordinate y is determined and corrected on the basis of detecting the passage of the bottle in front of the photocells 22, 23 and the possible differences between the times at which this passage measurement occurs, as will be explained in more detail below. The unit 12 for calculating possible corrections makes for example a very fine resolution in determining the above-mentioned differences, for example a resolution of about 100 mus at the speed of the conveyor as described above. The use of laser photocells enables the generation of radiation in a highly collimated beam with a very narrow cone shape (a beam with a substantially punctiform cross-sectional dimension), thus minimizing the errors in detecting the passage of the bottle.

Not shown is a device for actuating the means 10, in particular the position determining unit 11, for example a device similar to the device 6 for actuating the robot, may be provided upstream of the means 10 to associate the correction with the bottle. Such devices are used by bottle tracking systems, in which it is generally evaluated, on the basis of the operating specifications of the particular device, whether the bottle to be handled arrives at the operating station where the robot 3 is mounted, and whether its position is correct.

For simplicity of the drawing, the supporting structure for the unit 11 of the device 10 is not shown. Such a structure is fixedly connected to the conveyor 1 and to it in order to avoid as much as possible the vibrations brought by the same conveyor, thus ensuring the dynamic stability of the measurement.

Furthermore, the unit 11 must have mechanical rules for calibrating the system and compensating for positioning and alignment errors. More specifically, such rules must ensure the desired precision of the inclination of the photocells 22, 23. Again, the height of the unit 11 must be adjustable to accommodate the position of the laser sheet sensor 21 to the different formats of a multi-format production line.

To achieve the required measurement accuracy, the alignment of the unit 11 with respect to the conveyor 1 can be achieved in the mounting step by the system 30 temporarily associated with the unit 11 and the conveyor 1 in this step. For example, as shown in fig. 4, such a system comprises a laser pointer 31 mounted on the unit 11, which laser pointer 31 is intended to illuminate a target 32 located on the conveyor 1. Alternatively, the target 32 may be associated with the unit 11 and the pointer 31 associated with the conveyor 1. The manner in which such systems operate is well known to those skilled in the art. Preferably, both the pointer 31 and the target 32 are only mounted during the alignment step, even though the elements associated with the unit 11 may be permanently mounted.

One possible exemplary embodiment of the method of the present invention will now be described. The correction calculated by the unit 12 is a relative correction, i.e. a null value indicates that the bottle is in the reference position and a non-null value indicates the range of displacements and signs transmitted to the robot 3 in order to move it into a position suitable for gripping the bottle.

With regard to the correction of the coordinate z, reference is made to fig. 5 and 6. As mentioned above, this correction is determined on the basis of a comparison of the vertical extent of the portion of the light beam intercepted by the bottle 2 with the vertical extent of the portion intercepted by the bottle at a reference position (or, equivalently, with the expected nominal height).

Fig. 5 shows three bottles 2a, 2b, 2c (e.g. with screw caps) and their positions relative to the laser sheet 210. For example, the bottle 2a has the desired nominal height (correctly screwed on the cap), and therefore it is in the reference vertical position; the height of the bottle 2b is greater than the nominal height (partially unscrewed cap) and the height of the bottle 2c is less than the nominal height (absence of cap).

Fig. 6 shows the output signal of the sensor 21, which is assumed, by way of example only and for clarity of description, to be a current signal at a minimum level (e.g., 4mA) when the light beam 210 reaches the detector 21B without being intercepted, and at a maximum level (e.g., 20mA) when the light beam 210 is completely intercepted. It will be apparent to those skilled in the art that such a signal consists of a series of pulses, each generated by the bottle 2 intercepting the light beam 210, the level of the (negative) peak of which is obviously dependent on the vertical extent of the portion of the light beam 210 intercepted by the bottle 2 and therefore on the bottle height. The pulses pz (a), pz (b), pz (c) correspond to the passage of the bottles 2a, 2b, 2c, respectively. For the sake of simplicity of the drawing, the sampling of the output signal of the sensor 21 as the bottle passes through is not shown.

In this exemplary embodiment, let:

iz (i), (ma) is the output current of the sensor 21 when the i (i ═ a, b, c) th bottle passes;

k (mm/mA) is the conversion constant of the sensor 21, for example by the relation:

K＝Δ/(Imax-Imin)，

given, where Δ is the height range detectable by the sensor, Imax, Imin are the maximum and minimum currents;

z (a), z (b), z (c) are the heights of the caps of bottles 2a, 2b, 2c relative to the bottom edge of beam 210, and

z0 is a value complementary to the height corresponding to the reference position (i.e., the value of the distance of the bottom edge of beam 210 from the top of the bottle cap of a bottle having a nominal height).

The coordinates z of the ith bottle are then iz (i) × K and the corrections cz (i) (if any) for the robot 3 are:

Cz(i)＝Iz(i)*K+Z0 (1)。

for bottle 2a, it is clear that current iz (a) will be such that iz (a) K-Z0, and hence cz (a) 0. For the bottles 2b, 2c, the conditions iz (b) < iz (a) and iz (c) > iz (a) occur, respectively, so that the value of cz (b) is positive and the value of cz (c) is negative, so that the gripper head 4 must be lifted or lowered, respectively, to move into the gripping position.

Obviously, the same principle can be applied, the output signal of the sensor 21 being a voltage signal with a positive maximum level when the light beam 210 reaches the detector 21B without interception, and the output signal of the sensor 21 being substantially 0 level when the light beam 210 is completely intercepted.

As mentioned above, in terms of the correction of the coordinate y, the bottle passing light beams 220, 230 are detected and, more specifically, the difference between the moments at which the bottle 2 reaches those light beams is measured.

Referring to fig. 7 and 8, which show the bottles centred on the axis a-a of the conveyor 1 and misaligned with respect to this axis, respectively, reaching the beams 220, 230, fig. 9 shows the output signals of the photocells 22, 23 in the case shown in fig. 8.

Assuming that the beams are arranged at the same angle (45 ° in fig. 7, 8) with respect to the axis a-a, the axis-centered bottles arrive at the beams 220, 230 at the same time, as shown in fig. 7. Conversely, if the bottle is off axis, one beam will be intercepted before the other. Fig. 8 shows a deviation to the right, so that bottle 2 intercepts first light beam 220 and then light beam 230.

Referring to fig. 9, assuming that the photocells 22, 23 provide voltage signals V22, V23, as will be apparent to a person skilled in the art, the voltage signals V22, V23 consist of a set of negative pulses (of which only one is shown, respectively denoted Py (22) and Py (23)), each corresponding to the interception of the light beam 220, 230 by the bottle 2, respectively. The falling and rising edges of the negative pulses of V22, V23 correspond to the entry and exit of the bottle 2 into and out of the respective light beam, respectively. Furthermore, when the light beams 220, 230 are not intercepted, it is assumed that the signals V22, V23 have a certain positive voltage (e.g., 24); and when the light beam 220, 230 is intercepted by the bottle 2, the voltage is substantially zero.

Setting:

cy (mm) is the offset of the bottle to the axis a-a of the conveyor (hence the correction range to be applied to the robot's coordinates y);

r (mm) is the distance between the actual entry point of the bottle into the beam 230 and the theoretical entry point (i.e., the entry point if the bottle is centered on the axis) along the bottle advancement direction F (i.e., the entry point if the bottle is centered on the axis);

dtf (ms) is the delay of the pulse Py (22) relative to the falling edge of Py (23);

v (x) (m/s) is the forward speed of the conveyor;

alpha is the angle of the beams 220,230 with the conveyor axis a-a,

then, by simple trigonometric analysis, for an angle α of 45 ° as shown in fig. 7 and 8, one can obtain:

Cy＝R/2 (2)

and, for a general angle α

Cy＝R/2*tangα. (3)

Obviously, the calculation of the correction cy (f) for the falling edge of the pulse Py (22), Py (23) for the angle α of 45 ° and the general angle α is given by the following equation:

Cy(f)＝v(x)*DTF/2 (4)

Cy(f)＝v(x)*DTF*tangα/2. (5)

in theory, using the pulse Py (22), the falling edge of Py (23) is sufficient to correct the position in the x-y plane. However, in practice, the use of a falling edge only makes the measurement sensitive to system misalignment errors and differences in divergence of the beams 220, 230. To alleviate this problem, rising edges may also be utilized. In this case, the delay of the rising edge of the pulse Py (23) with respect to Py (22) is expressed by DTR, and for an angle α of 45 ° and a general angle α, the correction cy (r) calculated using the rising edge is given by the following equation, respectively:

Cy(r)＝v(x)*DTR/2 (6)

Cy(r)＝v(x)*DTR*tangα/2. (7)

the actual corrected Cy may be, for example, an average of the values Cy (f) and Cy (r) or other combination of the same values. Alternatively, a correction coefficient proportional to DTF-DTR, for example, may be applied to the value Cy (f).

By using both edges of the pulse, the measurement sensitivity to system misalignment errors and beam divergence differences can be reduced by about one order of magnitude.

It should also be noted that the longitudinal position of the bottle (coordinate x) can also be detected from the moment the bottle 2 passes in front of the photocells 22, 23. However, this information item is not used, since the coordinates x can be calculated by the robot 3 in general on the basis of the information obtained from the actuating means 6 and from the unit controlling the movement of the conveyor 1. Therefore, only lateral correction is discussed herein.

The correction in the plane x-y is independent of the diameter coordinate as shown in figure 10. If the diameter changes, the moment of interception of the beams 220, 230 will change, but the relative time difference, which depends only on the shift amount Cy, will not change. Thus, it does not matter whether the light beams 220, 230 are intercepted by the cap portion or other portions of the bottle 2. For the same reason, in the case of a multi-format installation, it is not necessary to program the unit 12 again when starting the operation with bottles of different diameters.

It is apparent that the present invention can solve the above-described problems of the prior art. More particularly, the system is also able to correct for offsets that fall within the engineering range described above, as they can be deduced from the relationship described above with respect to the adjustment.

It is clear that the above description has been given only by way of non-limiting example and that changes and modifications may be made thereto without departing from the scope of the invention as defined in the appended claims.

More specifically, in terms of the correction of the coordinate y, when only one edge of the pulse of the signals V22, V23 is used, this edge may be a rising edge instead of a falling edge, because, if the beams 220, 230 are identical and perfectly collimated, and the system is perfectly aligned, there is the same temporal relationship for both the rising and falling edges.

Furthermore, contrary to the mathematical relationship given above as an example, different functions of the level of the output signal of the sensor 21 and the nominal height of the bottle (in terms of correction of the coordinate z) or the distance between the rising and/or falling edges of the pulses of the output signals of the photocells 22, 23 (in terms of correction of the coordinate y) may be used for the correction, these functions also depending on the particular sensor/photocell and the geometric parameters of the bottle.

Furthermore, as far as the correction of the coordinate z is concerned, even if this coordinate has been interpreted as the height of the top of the bottle with respect to the bottom edge of the light beam 210, it is clear that, by means of a suitable programming unit 12, the device 10 can directly provide the height with respect to the surface of the conveyor 1.