GB2218513A - Measuring device - Google Patents

Abstract

An apparatus for the three-dimensional assessment of an object comprises a laser distance-measuring device, means for mounting the object within range of said device, means for rotating the object and for moving the device linearly relative to the object and a computer for processing distance measurements to give the desired assessment of the object. The three-dimensional assessment of an object comprising rotating the object relative to a laser distance-measuring device, taking measurements of the positions of points on the surface of the object relative to other, pre-determined positions, feeding said measurements to a computer and processing them to give the desired assessment of the object. The device is used to determine the precise volume of bread loaves. <IMAGE>

Description

MEASURING DEVICE This invention relates to apparatus and methods for the three dimensional assessment of objects, in particular, to the assessment of objects using a laser distance-measuring device to take measurements over the surface of the object.

It may, for instance, be desired to measure the volume of a particular object. A known method of volume measurement, suitable for objects of various shapes, involves the casting of a shadow of the object onto a screen. The object is illuminated from one side and the shadow may, for instance, be cast onto a photoreceptor device. The measurements of the size of the shadow can then be related to the volume of the object. However, this method is unsuitable for determining the volume of an object with concave or re-entrant surfaces such as a loaf of bread having a somewhat enlarged and overhanging upper crust extending from a more uniformly shaped lower body portion.

Precise volume measurements are important for the quality control of bread manufacturing operations. Every batch of flour used by the bakery has to be evaluated by test baking to ensure that bread is made to a uniformly high quality. One of the aspects of this quality control is the measurement of the volume of the bread which can give information relating to the density of the bread crumb and the strength of the gluten in the flour. This information can then be used to modify the dough mix used in bread production in order to produce bread of the appropriate quality.This quality control procedure is important, not only as far as the inherent qualities of the bread are concerned, but also to ensure that the selected dough-piece weight produces bread that is of the appropriate dimensions for the standard tins used in the baking process, and is capable of being properly handled by automatic slicing machines and of being packed into standard sized bags.

Typically, a test bakery may bake several loaves of bread from each new batch of flour. The loaves have to harden for about 24 hours before their volumes can be determined.

The volume is conventionally determined by a displacement method. In one such method a standard loaf of known volume is used to determine the quantity of dried rape seeds needed to displace it in a container. The quantity of seeds displaced by the bread being assessed is then compared with this standard and the difference evaluated.

Since the rape seeds absorb moisture, care-has to be taken to control the humidity during the measuring process. It is not possible to use material, such as sand, which does not absorb moisture because such material will crush or compress the loaves. Light material such as polystyrene is not easy to handle because of static electricity effects. Because the results of test baking can only be obtained on the day following the baking, this limits the extent of control and monitoring possible through the test baking procedure.

It is desirable to have a precise and fast method for the measurement of the volume of loaves of bread in order to be able to control and monitor the bread-making conditions in the main bakeries.

According to the present invention, there is provided apparatus for the 3-dimensional assessment of an object comprising a laser distance-measuring device, means for mounting the object within range of said device, means for rotating the object and for moving the device linearly relative to the object and a computer for processing distance measurements to give the desired assessment of the object.

The present invention also provides a method for the 3dimensional assessment of an object comprising rotating said object relative to a laser distance-measuring-device, taking measurements of the positions of points on the surface of the object relative to other, pre-determined positions, feeding said measurements to a computer, and processing said measurements to give the desired assessment of the object.

The method and apparatus of the present invention can be used to determined accurately and quickly the volume of a loaf of bread, even though the bread may have concave or re-entrant surfaces which render inaccurate the use of a shadow projecting method as mentioned above. However, it should be appreciated that the distance measurements obtained by the laser device can be used for other purposes than the determination of the volume of a particular object. Other dimensional analytical uses include the measurement of length and/or width of the object, the measurement or presentation of various profiles of the object as well the combination of various measurements to produce other results, including combinations with other known parameters such as weight to produce density determinations.

In addition to the use of the method and apparatus for the present invention for dimensional analysis, the distance measurements may be utilised to produce, for instance, detailed archival records of the dimensional and other characteristics of objects, the production of computer graphics and animation and the appropriate control data to control the operation of numerically controlled machinery for the production of irregular and/or ill-defined objects involving the replication of one such object. For example, the measurements may be used to produce three-dimensional replicas of objects.

Apparatus in accordance with the present invention may be such that a large number of distance measurements may be taken enabling the 3-dimensional digitisation of objects with complex shapes and the entry of such data onto a computer system. Once the data is entered into a computer, it can be treated mathematically to yield the desired dimensional information or indeed, any physical parameter that can be defined mathematically.

As has been mentioned above, it is an advantage of the present invention that objects with complex shapes can be 3-dimensionally assessed. It is also an advantage that this assessment can be done rapidly, the results being obtained in a period ranging from a few seconds to a few minutes. In addition, the method and apparatus of the present invention is a non-contact method and therefore offers considerable advantages over contact and displacement methods, particularly in the 3-dimensional assessment of soft objects such as loaves of bread.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically apparatus in accordance with the present invention; and Figure 2 is a front perspective view of the part of the apparartus in Figure 1.

Apparatus in accordance to the present invention includes a laser distance-measuring device having a sensing head 1 including a laser beam projector 2 and a sensitive linear photo detector 3. Such a device determines the distance between the measuring head of the device and the point on the surface of the object impinged by the laser beam. The distance measurements obtained by the laser device having a sensing head 1 are fed to computer 4 which processes the data and which in turn is linked to a printer 5.

The sensing head 1 of the laser device is mounted within a cabinet 9 for linear vertical movement effected by means of motor 11 connected via belt 13 to guide follower 15 which is mounted on guide 17 and supports sensing head 1.

Within cabinet 9 there is also located turntable 19 mounted on support 21 so as to be rotatable by means of motor 23.

Turntable 19 carries at its centre a clamp 25 having pins 27 extending upwardly from the upper surface of the clamp 25. Mounted vertically above clamp 25 is a further clamp 29 having pins 31 extending downwardly from clamp 29.

Clamp 29 is mounted for rotation on arm 33 which in turn is connected to guide follower 35 mounted on vertical guide 37. The arrangement is such that upper clamp 29 can be moved vertically towards and away from lower clamp 25 so that a loaf of bread may be positioned between and held by clamps 25 and 29. Although the precise positioning of the loaf of bread is not important it would normally be arranged with its end engaged by clamps 25 and 29, as inaicated in Figure 1.

The above-described arrangement enables the mounted loaf of bread to be rotated about the vertical axis extending between the centres of clamps 25 and 29 and for the sensing head 1 of the laser device to be moved upwardly and downwardly along an axis parallel to but displaced from the above-mentioned axis of rotation of the loaf of bread.

The apparatus includes means for controlling the operation of motors 11 and 23 according to a pre-determined routine modified in accordance with initial readings as discussed below.

In operation, a loaf of bread is mounted in cabinet 9 between the two clamps 25 and 29. The door (not shown) of the cabinet is closed and automatically bolted for safety reasons. Operation of the apparatus is initiated and the sensing head 1 of the laser device is moved vertically, initially so as to locate the lower end of the loaf of br-ead. Once this end is located the sensing head 1 then continues vertically to locate the opposite end. Once both ends are located the turntable 19 is rotated so as to cause rotation of the loaf of bread about the vertical axis between clamps 25 and 29 as the sensing head is moved down on the turntable 19. During this movement the laser takes repeated measurements and accordingly traces out a spiral scan of data measurements over the object surface.

Once the lower end of the loaf of bread is reached, the sensing head is "parked" in a safe position and the door is unbolted to facilitate removal of the object.

The sampling of readings produced by the laser device is synchronised with the angular rotation of a loaf of bread so that successive readings are taken at 30 intervals. The readings are fed to the computer 5 which also controls the machine operation, including the spiral path pitch interlocks, sequencing and laser control. The scanning is continued until the end of the object is reached and this position can be located using a preliminary scan of the object. For the measurement of loaf volume, typically 4,000 data points are measured every 30 on a spiral scan of 5mm pitch. The time taken for the scan depends on the size of the object being measured, but for a typical loaf and 35 measurements taken per second, the scan time is about 2 minutes. The volume of the loaf may be measured with a repeatability of + of the measured volume.It should be appreciated that this cycle time is dependent on the speed of the laser device as well as the bread volume. Using another faster system, the scan time may be reduced by a factor of 100 or more.

Calculation times again vary with object size and scan pattern, but are typically about 20 seconds for a loaf of bread. The laser device gives an output related to the separation of the surface of the object from the laser.

Accordingly, calibration is required to relate this output to the value of the object radius, that is to say, the distance from the point on the surface of the object to the central axis about which the object rotate.

In calculating the volume of the loaf of bread it is assumed that each radius measurement corresponds to the average radius over, for example, a 30 sector of object surface. The volume of this sector is equal to r2Od/2 where r is the object radius, 0 is the angle in radians between measurements, and d is the thickness of the sector which is equal to the pitch of the scan.

To calculate the volume of the object, it is necessary to sum the volumes of all the wedges as follows:

In practice, as mentioned above, the output of the laser device is related to the separation of the laser from the surface of the object and calibration is required. If the calibrated values of r2 can be obtained from a look-up table, the formula for the volume is as follows:

If it is desired to calculate the length of the object then this can be easily obtained by dividing the number of data points measured by the scan pitch.

As will no doubt be clear, sufficient information is fed into the computer as a result of the measurements made by the laser device, to create a 3-dimensional model of the scanned object. Furthermore, any desired dimensional information can be extracted if a suitable software routine can be established. For example, in the case of loaves of bread, the "break" position of the loaf can be located , or the loaf height variation along the length of the loaf can be evaluated. As a further example, apparatus in accordance with the present invention can be used to measure the volume of baked goods e.g. sponges, where cracking of the surface has occurred, and to monitor such cracking as an aid to eliminating it.

In a modification of the method and apparatus of the present invention, use could be made of a line laser (a charge coupled device) and camera, with appropriate adjustment to the data processing calculations. This removes the need for vertical scanning of the object since the line laser measures the object at a number of different positions simultaneously.

In a further modification of the methods of the present invention, advantage can be taken of the fact that objects such as loaves of bread do not require measurements to be taken at such closely spaced intervals over the whole of the length of the loaves. The cross section of the loaf does not change rapidly in the middle of the loaf. It is possible to use a combination of a fine scan at the ends of the loaf and a coarse scan over the centre to speed up the scanning process. The calculation routines are modified accordingly. In general it may be possible to optimize the scanning pattern according to the nature of the object being assessed.

If the surface of the object changes rapidly or if there is a rapid change in surface colour or texture, the laser device may miss data. The calculation routine can be modified to allow for such missed data by, in effect, fitting an appropriate spiral over such data.

The data fed to and stored in the computer can be used to create computer generated images of the object which can then be manipulated using appropriate software to give views of the object from any viewpoint. The data can also be used to reproduce three-dimensional representations of the object.

Claims (12)

1. Apparatus for the three-dimensional assessment of an object comprising a laser distance-measuring device, means for mounting the object within range of said device, means for rotating the object and for moving the device linearly relative to the object and a computer for processing distance measurements to give the desired assessment of the object.

2. Apparatus according to Claim 1, characterised in that the laser distance-measuring device comprises a laser beam projector and a sensitive linear photo detector.

3. Apparatus according to Claim 1, characterised in that the laser distance-measuring device comprises a charge coupled device and camera.

4. Apparatus according to any of the preceding claims, characterised in that the means for mounting the object to be assessed comprises clamps for engaging the object, the clamps being mounted such that an object engaged by the clamps may be rotated about one of its axes.

5. Apparatus according to any of the preceding claims and substantially as herein described with reference to the accompanying drawings.

6. A method for the three-dimensional assessment of an object comprising rotating said object relative to a laser distance-measuring'device, taking measurements of the positions of points on the surface of the object relative to other, pre-determined positions, feeding said measurements to a computer and processing said measurements to give the desired assessment of the object.

7. A method according to Claim 6, characterised in that the said laser distance-measuring device comprises a laser beam projector and a sensitive linear photo detector.

8. A method according to Claim 6, characterised in that the laser distance-measuring device comprises a charge coupled device and camera.

9. A method according to any of Claims 6 - 8, characterised in that the object to be assessed is engaged by means of clamps mounted such as to allow rotation of the object about one of its axes.

10. A method according to any of Claims 6 - 9, characterised in that the assessment of said object comprises determination of one or more of the volume, external dimensions and density of the object.

11. A method according to any of Claims 6 - 10, characterised in that the said measurements fed to the computer are processed so as to produce one or more profiles of the object.

12. A method according to any of Claims 6 - 11 and substantially as herein described with reference to the accompanying drawings.