Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1999-11-23
2001-07-17
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S078000
Reexamination Certificate
active
06260419
ABSTRACT:
TECHNICAL AREA
The invention relates to a process and a device for conducting a hardness test on test specimens, especially tablets or pills, in accordance with the preambles of claims
1
and
5
.
PRIOR ART
In the course of quality control in the fabrication of tablets, the physical properties of tablets, such as, for example, weight, dimensions, disintegration time in a medium and hardness, are determined. For this purpose, tablet testing systems have been developed, each of which can examine numerous tablets from a production cycle in terms of these properties. Tablets of a batch are separated in a storage bin and conveyed on a conveyor belt, for example, from one measurement station to the next.
The hardness of the test specimen is usually measured in a dynamometer cell, whose key components are a pressure piston and a thrust bearing. In order to carry out the hardness test, the test specimen, that is to say, the tablet, is conveyed into the region between the pressure piston and the thrust bearing, whereby the tablet preferably comes into contact with the thrust bearing. The pressure piston is then moved against the thrust bearing and thus against the tablet lying in front of it by means of a stepping motor. The force exerted by the pressure piston with each step of the motor is measured and recorded. This force is constant and very small as long as the pressure piston does not come into contact with the tablet or when it is just pushing it over the testing table without the counterpressure of the thrust bearing. Once the pressure piston comes into contact with the tablet and presses it against the thrust bearing, the force exerted by the pressure piston increases with each step of the stepping motor until the tablet breaks apart. The force employed to break apart the tablet is recorded and serves as a measure of the hardness of the tablet. The abrupt drop in the force employed by the pressure piston in breaking apart the test specimen serves as a termination condition for ending the measurement. The pressure piston is retracted to its starting position and the next tablet can be tested.
In order to afford meaningful, reproducible hardness values, the hardness measurement, that is to say, the crushing of the tablet between the pressure piston and the thrust bearing, should always occur along a defined axis. Attention should be paid to this in the case of tablets that are not symmetrical in shape, if only for the fact that a thickness measurement is often carried out at the same time as the hardness measurement. Consequently, the position of the pressure piston when the hardness measurement is terminated serves as a measure of the thickness. Furthermore, it is entirely possible for tablets of this kind to have different hardness values along different axes.
In the case of tablets with an elongated ellipsoid shape, the alignment during conveyance on the testing table is accomplished passively, for example, by means of a slide, which aligns the tablets transversely to the direction of conveyance. However, irregularly shaped tablets are difficult to align passively in this manner. Therefore, when the hardness of such tablets is measured, greater measurement errors have to be anticipated in the conventional testing systems.
In order to avoid such measurement errors, it is known to actively align the tablets so that their preferred direction, along which the hardness is to be measured, coincides with the direction of movement of the pressure piston against the thrust bearing. For this purpose, the position and alignment of the tablet between the pressure piston and the thrust bearing on a testing table is recorded with a camera and evaluated by means of image processing. The image data make it possible to determine by how many degrees the preferred axis of the test specimen deviates from the direction of movement of the pressure piston and the thrust bearing. This deviation can then be corrected by suitable measures.
A device is known for this purpose with which the tablet is situated on a rotary testing table. The dynamometer cell, in particular the pressure piston and the thrust bearing, are fixed in place. The direction of the hardness measurement is thereby fixed. The testing table is then rotated—under the control of the camera signal—until the preferred axis of the test specimen coincides with the direction of movement of the pressure piston against the thrust bearing. Thus, a hardness measurement is accomplished in the direction of the preferred axis of the test specimen.
However, a drawback of devices of this kind is that the time required to align the test specimen in the direction of movement of the pressure piston is often very long. The reason for this lies in the fact that the movement of the test specimen by rotation of the testing table is very difficult to control owing to the low friction between the test specimen and the testing table.
This can have the consequence that the test specimen often follows the rotary movement of the testing table only partially or not at all. Furthermore, the test specimen, once set in motion, continues to rotate further, even when the testing table stands still. Therefore, after each rotation of the testing table, it is necessary to redetermine the position and preferred axis of the test specimen and, if necessary, to rotate the testing table by way of correction. This is repeated as many times as necessary until the preferred axis of the test specimen coincides, within certain tolerances, with the direction of motion of the pressure piston. Only then can the hardness test be carried out. Therefore, the drawback of this active adjustment of the preferred axis of the test specimen lies in the fact that it often calls for several corrective operating steps for the adjustment; that is to say, the drawback lies in a high computational effort.
TECHNICAL OBJECTIVE
The invention is therefore based on the objective of developing a process and a device for carrying out a hardness test for test specimens, in particular tablets or pills, in which the alignment of the test specimen relative to the pressure piston and the thrust bearing is effectuated in a short time and with little computational effort.
DISCLOSURE OF THE INVENTION AND OF ITS ADVANTAGES
The attainment of the objective consists, in accordance with the invention, in a process for carrying out a hardness test on test specimens, wherein the test specimen is conveyed on a testing table between a pressure piston and a thrust bearing, and the hardness of the test specimen is measured by pressing the pressure piston and the thrust bearing against each other, whereby, in an optical or acoustical manner, the spatial position of a preferred axis of the test specimen is determined. Here, the preferred axis is the axis along which the hardness test is to be carried out—for example, the lengthwise axis of the test specimen. Furthermore, correction data are determined, which are dependent on these positional data as well as on the position of the pressure piston and the thrust bearing, whereby the position of the pressure piston and the thrust bearing can be determined in the same way as is the position of the test specimen or else electronically from the position of control elements used for moving these elements or from the preceding measurement. On the basis of these correction data, the pressure piston and the thrust bearing are moved relative to the test specimen, whose position is unchanged on the testing table, in such a way that the test direction, that is to say, the direction in which the pressure piston and the thrust bearing press against each other, coincides with the direction of the preferred axis and the thrust bearing is brought into the immediate proximity of the test specimen. The hardness of the test specimen is then determined in the known way by pressing the pressure piston against the test specimen, while the position of the thrust bearing remains unchanged.
Furthermore, the attainment of the objective consists, in a device for carrying out a hardness test on test spe
Kasper Horst M.
Noori Max
LandOfFree
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