GB2189886A - A measuring device - Google Patents

Abstract

A measuring device is provided, particularly for measuring dimensions of articles such as containers. The device has an electrical transducer 101 or 102 of the type that gives an electrical signal dependent on the depth to which an operating element is depressed. The transducer is mounted on suitable means, such as a robot arm 13, for moving it along substantially the same line of action as that along which the operating element is depressed. The device determines the position, with respect to a datum position, of the mounting means along that line of action and from this and from the signal from the transducer, is able to determine the position of the operating element relative to the datum. A turntable 26 may be provided for supporting an article to be measured, such as a bottle. By turning the turntable through 180 degrees, a diameter of the article can be measured. <IMAGE>

Description

SPECIFICATION A measuring device This invention relates to a measuring device, particularly one for measuring dimensions of articles such as containers.

Existing devices for measuring articles such as glass containers include, for example, rulers, height gauges, manual calipers etc. A test using the manual instruments suffers from the disadvantages of being slow and subject to human error, the test is not controlled so as to be standardised and the conscientiousness with which the test is carried out cannot be checked.

Another existing device for measuring is a co-ordinate measurement machine. This is a machine which has a probe mounted on a gantry and capable of movement in three dimensions. The probe gives an on/off signal when it is touched and only requires a displacement of 0.2 microns to give the signal.

Such an accurate probe is itself very expensive and co-ordinate measurement machines in general, while giving electronically gathered data that can be verified, are nevertheless slow, expensive, complex to set up and not necessarily accurate, because curve-fitting methods are used by the software which can give poor results e.g. for a container having irregular surface features. To reduce the cost of such a device, it would not be sufficient to replace the on/off probe with an on/off microswitch because a switch, over its lifetime, is inconsistent in its point of switching and inevitably has a degree of hysteresis so that the point at which it switches from on to off is different to that at which it switches from off to on.

Co-ordinate measurement machines are expensive for the additional reason that the gantry or other mounting means has to be as accurate as the probe itself. It would be desirable to use a versatile and cheap mounting such as a robot arm but robot arms are generally driven by stepper-motors and rack and pinion arrangements. Stepper motors typically move in intervals of 400 steps per revolution and, depending on the gearing, a rack driven by such a motor typicaly moves in steps of about 0.03 mm. Such a stepper motor can be accurate to 3% of its arc so that the accuracy of each 0.03mm step is typically about 0.001mum.

As well as the relatively large steps of robot arms, most types of arm suffer from "backlash". "Backlash" arises, for example with a rack-and-pinion in which, on reversing the drive from the pinion, there is some movement of the pinion before the rack moves. It is known, in the field of robotics, to compensate for backlash when determining the position of an operating element, by always approaching an operating position from the same direction. If a micro switch were to be mounted on such an arm, then although the problem of hysteresis in the switch could be avoided by the same technique-ie. always activating the switch in the same direction, e.g. from off to on, there would still be a problem in that there could be occasions when it would not be possible to operate both the arm and the switch in their respective chosen directions.Micro switches have a further disadvantage in that they require quite a high operating force.

The present invention provides an improved measuring device.

According to the present invention, there is provided a measuring device comprising an electrical transducer (the first transducer) of the type that gives an electrical signal the size of which is dependent on the depth to which an operating element is depressed, mounting means for the transducer for moving it along substantially the same line of action as that along which the operating element is depressed and means for determining the position, with respect to a datum position, of the mounting means along that line of action whereby, from the position determining means and the signal from the transducer, the position of the operating element relative to the datum can be determined.

The mounting means may be an articulated arm capable of bringing the operating element of the transducer to bear on an article from different angles around the article. A turntable may be provided for supporting an article to be measured, the line of action of the transducer and the mounting means passing approximately through the centre of the turntable, and means may be provided for determining the angle of rotation of the turntable.

Preferably the mounting means are also capable of vertical movement, a control processor is provided, arranged to control movement of the mounting means and the turntable and to monitor the height of the mounting means, the position of the operating element relative to the datum and the rotation of the turntable, so as to measure diameters of the article at various heights and a memory is provided, arranged to contain predetermined diameters corresponding to predetermined heights, wherein the processor is arranged to compare the measured diameters with the predetermined diameters and give an indication when a measured diameter differs from a corresponding predetermined diameter by more than a predetermined amount.

A second height-determining electrical transducer may be provided mounted on drive means, for indicating the height between the height determining transducer and the turntable, wherein the memory is also arranged to contain a predetermined height and the processor is arranged to compare the measured height with the predetermined height and give an indication when a measured height differs from the predetermined height by more than a predetermined amount. Preferably means are provided such as gripper jaws for lifting an article and depositing it approximately centrally on the turntable. Preferably input means are provided for identifying to the processor the article to be measured, and the processor is arranged to select the predetermined diameters corresponding to predetermined heights from memory, according to the said input means.

Holding means may be provided for holding the article on the turntable. These may comprise a rod, drive means for lowering the rod onto or into the article and base holding means at the lower end of the rod for pressing the article against the turntable, or they may comprise a rotatable gripping device for gripping the inside of the article, near the top thereof and allowing it to rotate with the turntable.

At least one input conveyor and at least one output conveyor may be provided, each being controlled by the processor, for presenting articles for placing on the turntable and for removing articles which have been removed from the turntable.

According to a further aspect of the invention, there is provided a turntable and holding device for holding an article in position at an operating station, comprising a turntable, a suction pad, and means for raising the suction pad above the surface of the turntable and applying a downward force to the suction pad,which means for raising and applying a downward force may be a piston in a cylinder.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an elevation of a measuring device according to the invention; Figure 2 is a plan of the device of Figure 1, with certain components removed; Figure 3 is a schematic representation of parts of a device according to the invention, in elevation, with a bottle in position for measuring; Figure 4 is a plan of some of the parts shown in Figure 3; and Figure 5 is an elevation of the turntable and holding device according to the further aspect of the invention.

Referring to Figure 1 and 2, a test bench 10 is shown, on which sits a robot generally indicated at 11. The robot comprises a stand 12 and an arm 13. The stand 12 and arm 13 are capable of rotating in a horizontal plane and the arm is capable of extending along its length.

At the end of the arm 13, there is a stepper-motor 14 and a vertical tube 15. Associated with the motor 14, is a pinion (not shown) which engages a rack 16 fixed along the tube 15. At the lower end of the tube 15, there is a gripper 20 and a transducer assembly 100 (Figure 3) having a horizontal transducer 101 and a height transducer 102 mounted thereon. The gripper 20 and height transducer 102 are shown mounted on opposite sides of the tube 15, with the horizontal transducer 101 at 90" to each of these forming an assembly which is rotatable about the axis of the tube 15, by means of a steppermotor 22 mounted at the top end of the tube and having spindle (not shown) extending down inside the tube.

Mounted on the bench 10, at a measuring station 25, there is a turntable 26 which rotates in a horizontal plane, driven by a stepper-motor 27. Extending up beside the turntable 26 is a post 28, which can be driven vertically by a motor, gearbox and rack and pinion, generally shown at 24. On top of the post 28 a holding device is mounted, generally indicated 29. (As an alternative, its holding device 29 may be fixed to the moving component of a rodless cylinder mounted on the bench 10.) The holding device may take a number of forms, described later.

Stepper-motors 14, 22 and 27 are driven by pulses and the number of pulses determines the extent of their rotation. For the robot itself, the sizes of the steps of movement in its various directions are approximately as follows: Z-axis (up and down movement of tube 15)-0.026 mm rotate (horizontal rotation of stand 12 and arm 13) - 0.015 extend (telescopic extension of arm 13)-0.032 mm yaw (rotation of tube 15)--0.047" On the bench 10, there are also four conveyors IP1, IP2, OP1 and OP2 and a control processor 30, havng a VDU monitor 3. The conveyors can be controlled both manually by stop/start buttons 32-35 and by the processor 30.At the forward end of each conveyor, there is a light sensor (or a micro-switch) 36, 37.

The arm 13 of the robot 11 is not shown in Figure 2, but the arcuate area of operation 40 is shown. In the area of operation, there is also shown a calibrating object 41 which may be a granite block, for example.

Figures 3 and 4 show in more detail the arrangement of the device at the measuring station 25. In addition to the tube 15, rack 16, grippers 20, transducers 101 and 102, turntable 26 and post 28 already described, there is shown a bottle B in position for measuring on the turntable 26. In this Figure, the holding device 29 is shown to comprise a holding rod 45 driven vertically by the motor 24 (Figure 1). At the free end of the rod 45 is a holding pad 47.

Transducers 101 and 102 are of the inductive type and are driven by an A.C. signal so as to give a response dependent on the depth to which their respective operating elements 103 and 104 are depressed. The signals from the transducers are fed to analogue-to-digital converters (not shown) which convert their outputs to a binary number from 0 (no depression) to 4096 (full depression). The operating elements have a stroke of 3mm, so the accuracy of the transducer output is better than + or - 0.001 mm. This can be compared with a switching-point hysteresis differential of 0.05mm for a heavy duty micro switch requiring an operating force of 3709, or 0.13mm for a lighter switch requiring an operating force of 1429. It can also be seen that such transducers give the device an accuracy which is an order of magnitude greater than the step-size of the robot.

Mounted on the operating element 103 of horizontal transucer 101, is a D-section metal rod 105 of 100mm-150mm length. Thus when the rod 105 is pressed horizontally on its flat face, the operating element 103 is depressed. Mounted on the operating element 104 of height transducer 102 is a roller 106 turning about a horizontal axis. When the roller is pressed upwards, the operating element 104 is depressed. A third transducer 107 is provided on the side of the tube 15 opposite to the horizontal transducer 101. This third transducer has a chisel-shaped prism 108 on its operating element and its function is described later.

It will be appreciated that these transducers could be mounted in a number of alternative suitable positions.

The centre line of the robot arm 13 is shown by the line 110.

The signals from the analogue-to-digital converters connected to transducers 101, 102 and 107 are relayed to the processor 30. The position of the robot arm 13 both in rotation and extension, the height of the transducer assembly 100, the orientation of the turntable and the rotation of the tube 15 are already known to the processor 30 from a count of the pulses fed to them.

The operation of the robot and its associated elements is as follows.

The processor 30 guides the robot to a starting position, at which the counts are zeroed.

The processor 30 guides the robot to a position where the grippers 20 can pick up an article, for example a bottle, from one of the input conveyors IP1 or 1P2. The grippers are closed around the "finish" F of the bottle, the tube 15 is raised and the bottle is moved to the turntable 26 and deposited thereon. The holding rod 45 is now lowered by means of the motor 24, so that the holding pad 47 is extended into the bottle until it holds the base thereof firmly against the turntable 26. The gripper 20 now releases the bottle and withdraws. The turntable can now turn with the bottle.

The tube 15 is rotated through a quarter turn clockwise and horizontal transducer 101 with its rod 105 is advanced towards the bottle by rotation of the robot as a whole.

Whenever the transducer assembly 100 is advanced towards or withdrawn from the bottle, the arcuate movement of the arm 13 in rotation is combined with telescopic extension movement and yaw movement about the tube 15 so that the line of action 111 of the appropriate transducer, in this case transducer 101, always passes through the centre of the turntable 26, as shown.

The measuring process is now ready to begin. The processor guides the transducer 101 to a starting height near the base of the bottle B by means of stepper-motor 14, the height being determined from the stepper-motor 14.

At this pre-determined height, the transducer 101 is advanced towards the bottle as described until a displacement signal is given by transducer 101. From the number of steps through which the robot has rotated, the length of the robot arm and the signal from the transducer 101, the position of the wall of the bottle B at its particular orientation is measured. The position is recorded in an array, in terms of the distance of the bottle wall from the centre of the turntable, together with the corresponding height and angular position of the turntable as determined from the number of pulses fed to stopper motor 27.

The turntable is now turned, through an increment of a few minutes of arc, corresponding to a step or a number of steps of motor 24, with the bottle B on it. The robot arm rotates (and the calipers yaw) if necessary and a new measurement is made. Thus, if the signal from transducer 101 increases above a predetermined value, then the transducer is withdrawn one or more steps and likewise, if it falls below a predetermined value, then it is advanced. After recording the measurement, the turntable is rotated through another increment and the next measurement made.

When a full rotation of the turntable 26 has been completed, the processor is able to determine the maximum and minimum diameters of the bottle B. It simply pairs together measurements taken 1800 apart and adds together each pair.

Having determined the maximum and minimum diameters at the lowermost predetermined height, these values are stored in the memory of the processor 30 and the steppermotor 14 is driven to a second height, so that the calipers are positioned higher up the bottle B. The operation is now repeated for a further rotation of the turntable and a second pair of diameter values are stored. Further pairs are obtained at different heights, with the transducer assembly 100 progressing up the bottle B until a final measurement is made at the finish F (Figure 3). The processor now has in memory a table of maximum and minimum diameters versus height.

Transducer 101 is now withdrawn, the tube 15 is rotated through a quarter-turn (clockwise) and the height transducer 102 is brought into position over the top of the bottle B. The tube is lowered until a signal is given by transducer 102 indicating that it has touched the bottle. The signal from transducer 102 and the position of stepper-motor 14 indicate the height. (As a datum for the height measurement, the height transducer is lowered to the level of the turntable 26 and the height of that is measured. The difference between these is the height of the bottle. This can be done for each article or only periodically). The turntable 26 is again turned and the maximum and minimum heights measured.If desired, further measurements can be recorded, giving the height at different intermediate rotations and, from the readings given, the degree of warp or dip of the top of the finish F can be assessed, and distinction can even be made between the warp and dip types of deformation.

The measurements on the article have now been completed and the height measurements added to thetable in the processor memory.

The processor now compares those measurements with predetermined measurements in a permanent memory, in the form of pairs of diameters with tolerance ranges and height tolerances. If any one of the measurements falls outside the predetermined permissable range, the processor indicates the article is not to the specified size.

Having described the measuring operation on a single article at the measuring station 25, the overall operation for measuring a batch of articles will now be described in relation to containers.

A particular design of containers for which measurements are to be made is identified to the processor 30 by keying in the design number and finish code. Containers of that design are then loaded onto the input conveyors in mould number order. It is generally found that if one container from a mould is not to the specified sizes, then it is likely that so too are further containers made from that mould, so it is only necessary to take one, or perhaps two containers from any one mould.

The operating sequence can now begin and all the operations described below are controlled by the control processor.

A list of nominal dimensions, tolerances and measuring positions is called from memory, identified by the job number and finish code.

This is called the specification data and gives all the necessary information to carry out the measuring operation.

The controller 30 instructs the input conveyor IP1 to be stepped forward by a distance approximately equal to the diameter of the container, as determined by the specification data or until a container interrupts the light sensor or microswitch 36.

The controller now instructs the robot arm to move the position of the first container the exact position for picking up the container being determined by the specification data. The robot then picks up the container by means of gripper 20 and moves to the turntable 26 and deposits the container thereon. The exact positon for depositing the container is again determined by the specification data.

The measuring procedure is now followed, as described above. The starting height of the transducer assembly, the subsequent measuring position heights are the position to which the height transducer 102 is to be moved, are all specified by the specification data, as also are the predetermined measurements and tolerances with which the measurements are to be compared. These predetermined measurements are derived from the engineering drawings of a nominai or ideal container.

When all the measurements of a container have been made, the results of the measurements and the deviations from specification are displayed on the VDU monitor 31 and the grippers 20 pick up the container again and move it to output conveyor OP1 which is then stepped forward by an amount equal to the diameter of the container, in readiness for the next container. The input conveyor IP1 is stepped forward as before and the sequence is repeated.

When the processor 30 determines that input conveyor IP1 is empty, e.g. by counting the number of steps until each conveyor has travelled its full length, then conveyor IP2 is stepped forward and containers are lifted from it, they are measured and are deposited on conveyor OP2. When conveyor IP2 is empty, the whole operation stops. The containers are now loaded on the output conveyors in the same order as they were loaded on the input conveyors and all the results of the measurement are available for display on the VDU monitor 31. The monitor shows the mould number of any defective container and appropriate action can be taken to rectify the defect.

Periodically it is necessary to check the accuracy of the apparatus and for this an inert calibrating object 41 can be provided. A preprogrammed calibrating routine can be run to take measurements from the calibrating object 41 and record variations in the measuremnt obtained as compared with an earier calibration. The controller can compensate accordingly when making the next measurement run.

The apparatus described has the advantage over previous measurement techniques of great flexibility for moderate cost. Thus it is envisaged that the apparatus can be used for any one of more than 2,000 different designs of containers. Indeed, it is not necessary that all the containers in a batch are of the same design, as it is possible for the processor to call up a new set of design data during a complete run. A further important advantage of the apparatus is that, with automatic loading and unloading of the container and automatic data gathering, the apparatus can run at a moderate speed without the need for human superivison during the test. Furthermore, the method of test itself can be pre-set, ensuring that measurements are made at specified points.

A number of variations on the described apparatus are possible. In particular, only one of a number of methods for holding the container on the turntable has been described.

The holding device described above, while being suitable for flat-bottomed or miniature containers, is not wholly suited to containers having a large push-up in the base. With such a bottle, the holding rod 45 is liable to step sideways and downwards. An additional holding device is shown in Figure 5.

Referring to Figure 5, a bottle B is shown in section on the turntable 26, also in section and an additional holding device is shown incorporated in the turntable 26. The device comprises a suction pad 120 on the end of a vertical tube 121 which is in connection with another tube 122 from which air is evacuated.

There is a rotating seal 123 between the two tubes 121 and 122 so that the suction pad 120 and tube 121 are able to rotate with the bottle B. Below the rotating seal 123 there is a short stroke piston and cylinder 124 which raises and lowers the vertical tube 121 and suction pad 120.

Once the bottle B has been deposited on the turntable 26, the piston and cylinder 124 operates to push up the tube 121 and the suction pad 120 into contact with the base of the bottle. Air is then withdrawn from the tube 122 and a downward force applied to the suction pad from the piston and cylinder 124. By suction between the pad 120 and the bottle, the bottle is held firmly on the turntable.

The holding device of Figure 5 is suitable for holding bottles having a large instep but less suited to bottles having embossed writing on the base. Using a combination of this suction holding device and the holding device of Figure 3, most typical containers can be accomodated.

Referring again to the holding device shown in Figure 3, the arrangement described requires a long rod and rack to extend below the bench. An alternative is to provide a pneumatic piston and cylinder of the type having a sliding seal. The cross-bar of rod 45 is attached to the sliding seal and rod 28 is an elongate cylinder with the cross-bar running up and down its length. A device of this type also provides a greater down-force on the holding pad 47.

Further alternative methods of holding the container would be to provide a chuck or a spider at the top of the post 28 which holds the top of the container from the outside and rotates about the same axis as the turntable 26.

A chuck could have a ring with, for example, three coplanar pins extending inwardly from the ring, with drive means to close the chuck around the container e.g. at its base. The ring could rotate about the same axis as the turntable 26 and be allowed a certain amount of lateral movement also.

Alternatively, a "spider" could be used, having three spokes meeting at a point, their spatial arrangement being that of three edges of a tetrahedron having an equilateral triangular base, the point at which the spokes meet being the apex of the tetrahedron, the apex being lowermost. The point of the spider is attached to a shortened version of rod 45 and the spider can be lowered by motor 24 so that the point protrudes into the mouth of the container and these spokes bear on the top of the "finish". Again, the spider should rotate about the same axis as the turntable and be capable of lateral movement to compensate for the top of the container being offset from a central axis. This can be achieved, for example, by means of a universal joint in rod 45.

If a spider is used and the height transducer is to be used to measure the height of a surface or shoulder, then it may be necessary to know where the spokes of the spider are, so that they do not obstruct the movement of the height transducer. This can be done by mounting a magnet on one of the spokes and having a Hall effect transducer mounted on the rod 45. When the magnet passes the transducer, the controller knows the location of the spoke and can predict its location as the spider rotates.

The device is not restricted to use with containers having rounded cross-sections but may be used on many different shapes of article, e.g. rectangular containers. In the case of such an article, the "diameter" that the device measures will merely be a transverse length dimension. Since all articles have a cylindrical "finish", the same gripping means 20 and holding means 29 can be used, regardless of the shape of the rest of the container.

In addition to the horizontal and height measuring transducers, further transducers can be added as desired. For example transducer 107 is provided with a chisel-shaped prism to access difficult points such as below the ridge for the tamper-proof bead or at the side of a protruding handle.

The operation of the device has been described above in terms of determining the maximum and minimum diameters of an article. Clearly, with the turntable being driven by a stepper-motor, much more information can be extracted as necessary, allowing, for example, diameter and/or height measurements to be recorded for comparison at differ ent intermediate positions around the article.

This can be done by, for example, completing a full revolution of measurements at a predetermined height, comparing these with the expected measurement from the specification data, determining the orientation of the article from this comparison and altering the datum angle of rotation of the turntable accordingly.

It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Claims (3)

1. A measuring device comprising an electrical transducer (the first transducer) of the type that gives an electrical signal dependent on the depth to which an operating element is depressed, mounting means for the transducer for moving it along substantially the same line of action as that along which the operating element is depressed and means for determining the position, with respect to a datum position, of the mounting means along that line of action whereby, from the position determining means and the signal from the transducer, the position of the operating element relative to the datum can be determined.

2. A device according to claim 1 wherein the mounting means are an articulated arm capable of bringing the operating element of the transducer to bear on an article from different angles around the article.

3. A device according to claim 1 or 2 wherein the line of action of the transducer and the mounting means passes approximately through the centre of the turntable, and means are provided for determining the angle of rotation of the turntable.

3. A device according to claim 1 or 2 further comprising a turntable for supporting an article to be measured, the line of action of the transducer and the mounting means passing approximately through the centre of the turntable, and means for determining the angle of rotation of the turntable.

4. A device according to claim 3, wherein the mounting means are also capable of vertical movement, a control processor is provided, arranged to control movement of the mounting means and the turntable and to monitor the height of the mounting means, the position of the operating element relative to the datum and the rotation of the turntable, so as to measure diameters of the article at various heights, and a memory is provided, arranged to contain predetermined diameters corresponding to predetermined heights, wherein the processor is arranged to compare the measured diameters with the predetermined diameters and give an indication when a measured diameter differs from a corresponding predetermined diameter by more than a predetermined amount.

5. A device according to claim 4 further comprising a second, height-determining electrical transducer mounted on drive means, for indicating the height between the height determining transducer and the turntable, wherein the memory is also arranged to contain a predetermined height and the processor is arranged to compare the measured height with the predetermined height and give an indication when a measured height differs from the predetermined height by more than a predetermined amount.

6. A device according to any one of claims 3 to 5 further comprising means for lifting an article and depositing it approximately centrally on the turntable.

7. A device according to claim 6 when dependent on claim 2 wherein the means for lifting comprise a pair of gripper jaws mounted on the articulated arm.

8. A device according to claim 4 or 5 comprising input means for identifying to the processor the article to be measured, wherein the processor is arranged to select the predetermined diameters corresponding to predetermined heights from memory, according to the said input means.

9. A device according to any one of claims 3 to 8 further comprising holding means for holding the article on the turntable.

10. A device according to claim 9 wherein the holding means comprise a rod, drive means for lowering the rod onto or into the article and base holding means at the lower end of the rod for pressing the article against the turntable.

11. A device according to claim 7 wherein the holding means comprise a rotatable gripping device for gripping the inside of the article, near the top thereof and allowing it to rotate with the turntable.

12. A device according to any one of claims 4 to 9 further comprising at least one input conveyor and at least one output conveyor, each being contro!led by the processor, for presenting articles for placing on the turntable and for removing articles which have been removed from the turntable.

13. A turntable and holding device for holding an article in position at an operating station comprising a turntable, a suction pad, and means for raising the suction pad above the surface of the turntable and applying a downward force to the suction pad.

14. A turntable and holding device according to claim 13 wherein the said means for raising and applying a downward force is a piston in a cylinder.

15. A device according to any one of claims 1 to 12 in combination with a holding device according to either of claims 13 and 14.

16. A device substantially as hereinbefore described and as shown in the accompanyingdrawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 and 3 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A measuring device comprising an electrical transducer (the first transducer) of the type that gives an electrical signal dependent on the depth to which an operating element is depressed, mounting means for the transducer for moving it along substantially the same line of action as that along which the operating element is depressed a turntable for supporting an article to be measured, and means for determining the position, with respect to a datum position, of the mounting means along that line of action whereby, from the position determining means and the signal from the transducer, the position of the operating element relative to the datum can be determined.