WO2008058543A1

WO2008058543A1 - Procedure for the weighing of letters; letter balance; and use of procedure and letter balance

Info

Publication number: WO2008058543A1
Application number: PCT/DK2007/000505
Authority: WO
Inventors: Jan Pietraszek; Jan Pedersen; Hënning B. MOLLER
Original assignee: Ihpostal A/S
Priority date: 2006-11-16
Filing date: 2007-11-15
Publication date: 2008-05-22

Abstract

By means of a procedure for the weighing of letters and of a letter balance, both small and large letters of varying weight are conveyed on a conveyor belt towards two rollers turning against each other so that the velocity of the letters on the conveyor belt is different from the velocity of the rollers. By means of measuring the letters' velocity before and after they reach the rollers and by means of measuring the rollers' velocity before and after the letters come in contact with the rollers, as well as by measuring the power provided to the rollers, it is possible to determine, with great accuracy, the weight of individual letters moving at high velocity, which is a significant advantage when checking as to whether the letters are insufficiently stamped, given that the accuracy also ensures that correctly stamped letters are not identified as being insufficiently stamped.

Description

Procedure for the weighing of letters; letter balance; and use of procedure and letter balance

The invention consists of a procedure for the weighing of letters conveyed on a conveyor belt with a velocity V towards two rollers driven by a drive source, with the rollers turning against each other and each with a peripheral velocity P, and with each letter being conveyed between the rollers driven by the drive source.

The invention also consists of a letter balance with a conveyor belt on which the letters are conveyed with a velocity V, and of two rollers turning against each other with a velocity P and driven by a motor.

Finally, the invention consists of use of the procedure and of the device.

With large quantities of letters that must be sorted in post offices and checked for correct stamping by determining their weight, there is currently a problem with conventional mechanical balances that are too slow to ensure rapid checking as to whether letters are insufficiently stamped.

US patent no. 3,648,839 consists of a device for the weeding out of letters that are insufficiently stamped. The device consists of a conveyor belt on which letters are conveyed towards two rollers turning against each other, with the letters' velocity different from that of the rollers.

By measuring the difference in the rollers' velocity when the letters pass between them, it is possible to determine whether a letter is insufficiently stamped by comparing the rollers' velocity with a standard velocity measured for a letter with a given and known weight. According to the US publication, the device is thus not set up to weigh letters conveyed on the same conveyor belt where the letters conveyed are expected to be of different weights.

One of the objectives with the invention is therefore to arrive at a procedure and a letter balance that make it possible to weigh letters of varying weights that are being conveyed on a conveyor belt so that an actual mass is determined for each individual letter.

The invention fulfils the former requirement, with a procedure of the type referred to in Claim 1 , one of the characteristics of which is that the letters' weight is determined on the basis of their change in velocity, of the change in the rollers' peripheral velocity, and of the power supplied to the drive source, given that the letters' weight is determined on the basis of the function

m = F(I, ω_φr , ω_før , E^Z , v_φr , v_før , E_tah )

according to which

m is the letter's weight,

/is the rollers' moment of inertia d_efter is the rollers' peripheral velocity, when the letter leaves the rollers, ffl_før is the roller's peripheral velocity before the letters come into contact with the rollers v_en_er is the letters' velocity when they leave the rollers v _før is the letters' velocity before they come into contact with the rollers and E^ is the power provided by the drive source to the rollers, while

E_tab is the power lost when a letter is weighed. Both large and small letters of varying weights, conveyed on the same conveyor belt, can thus be weighed very accurately, which is important in order to determine whether a letter is insufficiently stamped, since no letters with correct stamping must be weighed and identified as insufficiently stamped. Naturally, neither is it desirable for too many insufficiently stamped letters to be identified as correctly stamped.

With the rollers being driven by the drive source for a period of time shorter than the time it takes the letter to pass through the rollers, or with the rollers accelerating while the letters pass between them, it becomes possible to shorten the measuring times and thereby adjust the rollers' velocity so that the velocity of weighed letters before passage by the rollers can be adjusted, with the letters arriving at the rollers being conveyed away from the rollers so that any pile-up or excessive distance between letters can be reduced.

Depending on how the procedure is adapted to a particular task, the power supplied to the rollers can be constant or variable.

Furthermore, ω_efter and ω_før can be measured by a measuring device and the power supplied by the drive source can be measured by a watt meter.

According to one embodiment of the invention, the first of the above- mentioned rollers can be a driving roller driven directly by the drive source and the other roller can be a follow roller driven by the first roller due to the friction between them.

According to another embodiment of the invention, the letter can be conveyed through a further set of rollers, one of which is another driving roller and is placed on the side of the letter opposite to that of the first driving roller.

Furthermore, the follow roller and/or driving roller can be moved so as to create distance between the rollers before the letter is received, after which the follow roller and/or the driving roller is moved back again.

According to the invention, the measuring device can be an encoder, a photo sensor system or a display device.

In addition, the letter's velocity V_før can be measured by a sensor system, an encoder or a display device.

According to the invention, the letter's velocity V_en_er when in contact with the rollers can be measured by the same sensor system by measuring on the most posterior part of the letter with respect to the letter's direction of movement.

According to one embodiment of the invention, the roller driven by the drive source can have a lesser or greater velocity than the letter's velocity V _før.

In another embodiment of the invention, the letter has a thickness and a mass midpoint such that the letter's thickness can be measured so that a distance between the letter's mass midpoint and a rotation axis of the roller driven by the drive source can be determined.

Furthermore, the letter's velocity V_eft_er can be measured while the letter is in contact with the rollers.

The invention also consists of a letter balance, including - a conveyor belt on which letters are conveyed with a velocity V, - a first roller and a second roller, turning against each other with a peripheral velocity P,

- a drive source to drive at least the first roller to give it a velocity, and

- a device for measuring the velocity of the first roller.

The letter balance can also include a measuring device for measuring the letter's velocity or position.

The measuring device can be a sensor system consisting of at least one sender and one receiver such that the letter's position can be measured; the sender and the receiver can be separated into two parts or mounted on the same device.

In one embodiment of the invention, the sensor system can consist of another sender and receiver so that the letter's velocity can be measured.

In another embodiment of the invention, the means for measuring the velocity of the first roller can be a photocell, a light-control device or an encoder.

Furthermore, the letter balance can include a thickness meter for measuring the letter's thickness.

The letter balance can also include a control unit for adjusting the drive- source velocity (slower or faster) on the basis of measurements received.

The letter balance thus also has a velocity sensor for measuring the velocity of the letters and rollers as well as a measuring device for measuring the power supplied by the motor.

In one embodiment of the invention, the velocity sensors for measuring the rollers' peripheral velocity consist of an encoder mounted on one of the rollers' axles and the velocity sensors for measuring the conveyor belt's velocity consist of a photo sensor mounted over the conveyor belt. The motor is mounted on one of the rollers' axles, while the other roller is driven by the first roller by means of friction.

As mentioned, the invention also consists of a use.

The invention will be described in more detail below, with reference to the drawings, in which

Fig. 1 shows a letter being conveyed towards the two rollers according to the invention,

Fig. 2 shows the letter in Figure 1 , after it has been conveyed between the rollers,

Fig. 3 shows the letter just before it leaves the rollers, while

Fig. 4 shows the letter after it has left the rollers.

As shown by the drawings, which very schematically outline the structure of the letter balance, it consists of a conveyor belt (not shown) that conveys letters 1 (placed perpendicularly) and also seen on the drawings from above, towards two rollers 5, 6, that turn against each other as indicated with arrows 7, 8.

The two rollers are driven by a single drive source (not shown), such as an electric motor, connected to one of the rollers 5, 6, while the other roller is in friction contact with the roller driven by the motor. The roller driven by the drive source has a lower or higher velocity than the letter's velocity V_f01-. In another embodiment of the invention, the rollers and the letter have the same velocity V_før.

The power supplied to the drive source can be determined in various, known ways, such as with a watt meter for measuring the current and voltage supplied to the drive source.

The letter moves towards the two rollers 5, 6 with a constant velocity in the direction shown by arrow 2. The letter's velocity can be determined by the schematically shown light barrier 3, since the time from when the letter's edge breaks the left light beam 2a until it reaches the right light beam 3b can be determined and thus also the letter's velocity before it reaches the rollers 5, 6.

When the letter, as shown in Figure 2, comes into contact with the rollers 5, 6, it will have the same velocity as the rollers' peripheral velocity. The rollers' peripheral velocity before, ωf_ør, and after, ω_eft_er, contact with the letter can be determined with the help of an encoder connected to the roller driven by the drive source. In another embodiment of the invention, the rollers' peripheral velocity can be determined with the help of a sensor system. Moreover, the letter's velocity V_efter during or just after contact with the rollers can be determined with the help of a sensor system. Moreover, the letter's velocity V_Θft_er during contact can be determined with the help of the same sensor system as used to determine its velocity Vf_ør before contact with the rollers.

The sensor system is shown in the drawings as light barrier 4, which has two light beams 4a, 4b. The sensor system can be in the form of a sender and a receiver that are separated by a distance through which the letter can move. Furthermore, the sensor system can be in the form of a device on which both the sensor and receiver are mounted. Fig. 3 shows the letter just before it leaves the rollers 5, 6 and has broken the left light beam 4a, while Figure 4 shows the letter when it has left the rollers 5, 6 and has broken the right light beam 4b.

In one embodiment of the invention, the first of the aforementioned rollers is a driving roller driven directly by the drive source while the other roller is a follow roller driven by the first roller due to the friction between them.

According to another embodiment of the invention, the letter can be conveyed through a further set of rollers, one of which is another driving roller and is placed on the side of the letter opposite to that of the first driving roller. It is thereby possible to correct for letters that vary from ordinary, flat letters and have uneven mass distribution or that are particularly thick, which shifts the mass midpoint with respect to the driving roller.

Furthermore, the follow roller and/or driving roller can be moved so as to create distance between the rollers before the letter is received, after which the follow roller and/or the driving roller are moved back again. In one embodiment of the invention, the follow roller moves away from the driving roller or the driving roller moves away from the follow roller; in yet another embodiment of the invention, the rollers move away from each other at the same time.

The driving roller's peripheral velocity can also be adjusted by adjusting the power supplied by the motor. Adjustment of the power supplied by the motor is controlled by a control unit, just as the rollers' peripheral velocity is adjusted on the basis of measurements of the letter's position. This is done by means of the control unit adjusting the rollers' peripheral velocity to a predetermined velocity before the letter is received between the rollers. As the rollers take hold of the letter, the rollers' peripheral velocity changes due to the resistance created as the rollers change the letter's velocity. The rollers' peripheral velocity is changed until the letter has left the rollers. Thereafter, the control unit once again adjusts the peripheral velocity on the rollers to the predetermined peripheral velocity.

The control unit can control the motor on the basis of measurements received as to the letter's and rollers' peripheral velocity so that the motor, when these measurements have been received, adjusts the rollers' peripheral velocity to the predetermined peripheral velocity.

In one embodiment of the invention, a set of input rollers that take hold of the letter and send it through the rollers is mounted between the rollers and the conveyor belt on which the letters are conveyed.

As mentioned previously, the measuring device for measuring the rollers' peripheral velocity can be an encoder. In another embodiment of the invention, the measuring device can be a sensor system or display device.

A display device is understood as a device by means of which images taken of a moving object are processed in order to determine a given factor, such as a velocity, or in order to determine whether a process is under control. For example, an image is taken of a roller at a particular time and compared with an image taken of the same roller at another time, and the difference between the images is used to determine the peripheral velocity of the roller with the help of an image-processing program.

The letter's velocity before contact with the rollers V_før can be measured by a sensor system, a display device or an encoder that is placed either on the above-mentioned input roller or on the driving roller. The letter's velocity during or just after contact with the rollers can also be measured by a sensor system, a display device or an encoder. As mentioned, the encoder can be placed on the axle in connection with the driving roller. In another embodiment of the invention, the sensor system for measurement of the letter's velocity before contact with the rollers can also measure the letter's velocity by measuring the letter's most posterior part before the letter has passed completely through the rollers.

The thickness and mass midpoint of individual letters can vary from one letter to another. In one embodiment of the invention, the letter's thickness is measured so that a distance between the letter's mass midpoint and a rotation axis of the driving roller is determined. This makes it possible to correct the measuring result and so determine the mass of individual letters more accurately.

Furthermore, in another embodiment of the invention, several sensor systems can be used for measuring the letter's velocity during its passage between the rollers. This results in several measurements that can make weighing of the letter more accurate. It is also possible to detect a very uneven letter that can result in the measurements being unusable.

A sensor system is understood as all types of recording systems for the measurement of an object's velocity including, as previously mentioned, a light barrier that emits a light beam received by a receiver and that, when the light beam is broken, records that an object has moved out of the beam. The light beam can be light of any wavelength, including laser light, IR light or visible light. Furthermore, the sensor system can be a photosensor that also has a receiver and a sender. The sender and receiver can be mounted at a predetermined distance; the sender can also be mounted on the same device. The invention also consists of a letter balance that includes a conveyor belt on which letters are conveyed with a velocity V, a first roller and a second roller, turning against each other with a peripheral velocity P, - a drive source to drive at least the first roller to give it a velocity, and a device for measuring the velocity of the first roller.

In one embodiment of the invention, the letter balance includes a measuring device for measuring the letter's velocity or position, in which the measuring device is a sensor system consisting of at least one sender and one receiver so that the letter's position can be measured, and in which the sender and receiver can be separated into two parts or mounted on the same device. The sensor system can also consist of another sender and receiver so that the letter's velocity can be measured.

The way in which the letters' weight is determined is described more theoretically below.

The letter's power is:

EκiT = —mv² , where m is the letter's mass, and v is the letter's velocity.

In one embodiment of the invention, the rollers rotate with a constant peripheral velocity different from the letter's velocity. In this case, the motor constantly supplies power to the rollers. In another embodiment of the invention, the letter has the same velocity as the rollers' peripheral velocity.

The rollers' power is: ^Eκ_m = —Iar , where I is the rollers' moment of inertia and, ω is the rollers'

peripheral velocity.

The motor's power, E_motor, can be changed during the process and must therefore not be considered as a constant. If the motor is disconnected during the measurements, its power contribution can be left out of the calculations.

The power consideration now looks as follows:

Λ pBrev _ i pRuller pMotor _wk_ere

AE^ = ^Iω_φr -^Iω_M ² and .

Since AE^» _n ^rev = AE^«J^u'^er + E%% , as mentioned, gives

m = ^■ vefte, — V far

In this theoretical formula, consideration has not been given to the letter balance's loss of power during weighing of the letters. A loss E_tab of this kind can occur in the bearings in the follow roller, due to the air resistance on the letter and the lack of friction between the letter and rollers. E_tab is therefore introduced into the formula below.

co_før is measured with the encoder and v_før , v_e/rerand ω_eft_er are measured with the help of the light barriers.

Alternately, v_efter can be determined on the basis of ω_efter, given that the letter's full velocity is equal to the rollers' peripheral velocity when the letter passes through the rollers.

E_tii_fT_t ^can either be measured during weighing or be determined as a constant, while I is given by the rollers' geometry and weight.

The formula: m can be used both

theoretically and practically for determining the letter's weight. It has, however, been found that good results can be obtained by simplifying this formula. Research has shown that the weight can be determined very accurately on the basis of a simplified formula.

Research has also shown that when the number of letters to be weighed per time unit is very high, it may occur that the motor is unable to accelerate the peripheral velocity up to the predetermined level, which also means that cύ_før may vary from measurement to measurement.

The formula can generally be written as a function of all of the process parameters measured:

m = F(I, ω_φr , ω_for , E^ , v_φr , v_for , E_mh ) An empirically based function that has proven to determine the weight accurately is the formula m-i:

mx = ^a + ^bV _før + ^CVefier

Where a, b and c are empirically determined constants and include loss of power during weighing E_tab-

Greater accuracy in determining weight can be achieved with use of the formula m₂:

m₂ = a + bv_fgr + cv_efter + dv)_ør + ev_φr

Where a, b, c, d and e are empirically determined constants.

Since (0_før can vary, it is important, in certain cases, to include this variation in the formula m₃ so that:

W₃ = a + bv_fβr + cv _φr + dω_fβr

The mathematical formula for calculating the letter's mass can thus be more or less simplified. Which formula is most appropriate can depend on the measurement values. For example, the following may apply:

Where v_før > 3,Oim/s the following applies m = F_x (I, ω_φr , ω_fβr , E^₁ , v_efler , v_fgr )

Where v_fβr ≤ 3,Olm/s the following applies m = F₂{I,ω_φr,ω_fβr,E%::;,v_φr,v_fβr) Where F₁ and F₂ are mathematical functions that calculate the mass by means of various parameter conditions.

Which formula is used thus depends on the number of letters and their velocity. It can also be more appropriate to use one formula rather than another when the letters to be weighed have a focus weight-interval around, for example, 20 g, 50 g, etc. A formula can be chosen on the basis of letters of approximately 50 g, for example, being of particular importance.

Weighing accuracy of around 50 g is therefore considered to be of more importance than accuracy around 100 g or more.

If the position of the two following measurements of, for example, the letter's conveyance velocity V_før, is known, Vf_ør and v_efter in the two previous formulas can be reduced to one time measurement.

Advantages of choosing a more simplified formula can include easier calibration of the letter balance, improved weight intervals and/or simplified calculation and data processing.

Even though the intervention is described as the letters being conveyed between the rollers in the direction of axis X, there is no reason why the letters cannot be conveyed along the conveyor belt in the direction of axis X after which, when they arrive at the rollers, they can be moved in the direction of the Y axis, which means that v_fgr (in the Y direction) becomes 0.

Claims

PATENT CLAIM

1. Procedure for the weighing of letters conveyed on a conveyor belt, in which the letters are conveyed on the conveyor belt with a velocity V towards two rollers driven by a drive source, in which the rollers turn against each other, each with a peripheral velocity P, and in which each letter is conveyed between the rollers that continue to be driven by the drive source, with the characteristic feature that the weight of the letters is determined on the basis of the letter's change in velocity, due to a change in the rollers' peripheral velocity, as well as on the basis of the power supplied to the drive source, since the weight of the letters is determined on the basis of the function

m = F(I, ω_efter , ω_før , E%% , v_φr , v_fβr , E_lah )

according to which

m is the letter's weight, / is the rollers' moment of inertia βjefter is the rollers' peripheral velocity, when the letter leaves the rollers, ω_før is the roller's peripheral velocity before the letters come into contact with the rollers v_ef_ter is the letters' velocity when they leave the rollers v_før is the letters' velocity before they come into contact with the rollers and

^Ew_>°_t '^{s tne} P^ower provided by the drive source to the rollers, while

Etab is the power lost when a letter is weighed.

2. Procedure according to Claim 1 , in which the rollers are driven by the drive source for a period of time that is shorter than the time it takes the letter to pass through the rollers.

3. Procedure according to Claims 1-2, in which the rollers accelerate while the letters pass between them.

4. Procedure according to Claim 1 , in which the power supplied to the rollers is constant.

5. Procedure according to Claim 2, in which the power supplied to the rollers is variable.

6. Procedure according to each of the requirements 1-5, where ω_Θfter and ω_fø_r are measured by a measuring device and the power provided by the drive source is measured with a watt meter.

7. Procedure according to each of requirements 1-6, where the first of the aforementioned rollers is a driving roller directly driven by the drive source and the other roller is a follow roller driven by the first roller because of the friction between them.

8. Procedure according to Claim 7, in which the letter is conveyed through a further set of rollers, one of which is another driving roller and is placed on the side of the letter opposite to that of the first driving roller.

9. Procedure according to Claim 7 or 8, in which the follow roller and/or the driving roller move so as to create a distance between the rollers before the letter is received, after which the follow roller and/or the driving roller move back again.

10. Procedure according to each of Claims 1-9, in which the measuring device is an encoder, a photosensor system or a display device.

11. Procedure according to each of requirements 1-10, in which the letter's velocity V_f01- is measured by a sensor system, an encoder or a display device.

12. Procedure according to Claim 11 , in which the letter's velocity V_efter when in contact with the rollers can be measured by the same sensor system by measuring on the posterior part of the letter with respect to the letter's direction of movement.

13. Procedure according to each of requirements 1-12, in which the roller is driven by the drive source that has a lesser or greater velocity than the letter's velocity V f_ør.

14. Procedure according to each of requirements 1-13, in which the letter has a thickness and a mass midpoint and in which the letter's thickness is measured so that a distance between the letter's mass midpoint and a rotation axis of the driving roller is determined.

15. Procedure according to each of requirements 1-14, in which the letter's velocity V_efter is measured while the letter is in contact with the rollers.

16. Letter balance including:

- a conveyor belt on which letters are conveyed with a velocity V,

- a first roller and a second roller, turning against each other with a peripheral velocity P, - a drive source to drive at least the first roller to give it a velocity, and - a device for measuring the velocity of the first roller.

17. Letter balance according to Claim 16, that also includes a measuring device for measuring the letter's velocity or position.

18. Letter balance according to Claim 17, in which the measuring device is a sensory system consisting of at least one sender and one receiver so that the letter's position can be measured, and in which the receiver and the sender can be separated into two parts or mounted on the same device.

19. Letter balance according to Claim 18, in which the sensory system consists of another sender and receiver so that the letter's velocity can be measured.

20. Letter balance according to each of requirements 16-18, in which the means for measuring the velocity of the first roller is a photo cell, a light-control device or an encoder.

21. Letter balance according to each of requirements 16-20, that also includes a thickness meter for the measurement of the letter's thickness.

22. Letter balance according to each of requirements 16-21 , that also includes a control unit to adjust the speed of the drive source

(slower or faster) on the basis of measurements received.

23. Use of the procedure according to Claims 1-15 and of the letter balance according to Claims 16-23 for letter sorting.