Device for measuring tablet breaking force

There is provided a device for measuring the force required to break a tablet, wherein the device comprises a tablet holding means comprising a base, a tablet splitting edge in the base and an area for holding a tablet in an inclined cantilevered position such that at least a portion of the cantilevered segment of the tablet extends over the tablet splitting edge. Means are provided for exerting a force substantially normal to a portion of the cantilevered segment of the tablet extending over the splitting edge to thereby create a moment of force about the tablet splitting edge sufficient to break the tablet. The device includes means for measuring the force required to break the tablet.

BACKGROUND OF THE INVENTION 
This invention relates to a device for breaking a tablet, and in particular 
to a device for measuring the force required to break the tablet. 
Tablets have long been convenient dosage forms for a variety of materials, 
such as medicaments, vitamins, foods and detergents. It is important that 
each tablet be of the same weight and content of active material within 
close limits in order to ensure a constant dosage. In addition, each 
tablet must have sufficient hardness to withstand the shock of handling, 
packing and shipping. This latter requirement led to the development of 
hardness testers, such as the Strong-Cobb, Stokes-Monsanto, Pfizer and 
Heberlein hardness testers. These well-known devices are based on the same 
principle of operation, namely, diametral crushing of a tablet. 
In the Strong-Cobb tester, the force required to break a tablet across the 
diameter is produced by a manually or pressure operated pump. As the 
pressure increases, a plunger is forced against a tablet set on edge. A 
dial indicator records the final breaking force. 
The Pfizer hardness tester operates on the same mechanical principle as 
ordinary pliers. As the tablet is crushed in the jaws of the device, the 
force is recorded on a dial indicator. The dial indicator remains at the 
reading where the tablet breaks. It returns to zero when a reset button is 
pressed. 
The Stokes-Monsanto tester consists of a barrel containing a compressible 
spring held between two plungers. The lower plunger is brought into 
contact with the tablet. The upper plunger is forced against the spring by 
a threaded bolt and the force is transmitted against the tablet. As the 
spring is compressed, a pointer rides along a gauge in the barrel and 
indicates the pressure at which the tablet fractures. 
The Heberlein tester operates in a horizontal position. A moving anvil 
presses the tablet against a stationary anvil. As force is applied to the 
edge of the tablet, a pendulum swings away from its normal position. Its 
movement is followed by a pointer moving along a scale indicator. When the 
tablet breaks, the pendulum swings back to its original position while the 
pointer indicates the scale reading in both kilograms and in Strong-Cobb 
units. 
Compressed tablets are frequently orally administered to animals and 
humans. While tablets for animal and human consumption are normally 
available in unit dosages, it is frequently necessary to reduce the dose, 
such as by breaking the tablet in half, and consuming only half the 
tablet. Traditionally, tablets have been broken by hand. This can be 
accomplished by breaking the tablet between the second and third fingers 
of one hand while the thumb is used as a fulcrum or by using the index 
fingers of both hands while the thumbs serve as a fulcrum. 
It is important for the tablet formulator to have some indication of the 
force that will be required to break the tablet by hand. Tablets can then 
be formulated for specific uses. For example, persons with decreased 
strength in the hands or those suffering from diseases, such as arthritis, 
or those with handicaps, such as amputees, may encounter considerable 
difficulty in breaking tablets. The tablet formulator can provide such 
individuals with tablets that require a relatively low breaking force. 
When the tablets are manufactured, the manufacturer must be able to 
determine the breaking strength of the tablets for quality control 
purposes. 
Thus, there exists a need in the art for a tablet breaking device capable 
of measuring the force required to break the tablet. The measured force 
should be representative of the force that will be required for a human to 
break a similar tablet using one of the traditional manual methods. The 
tablets should break evenly in the device without crushing. Ideally, the 
device should be of relatively simple construction, easy to manufacture 
and simple to operate. 
SUMMARY OF THE INVENTION 
Accordingly, this invention aids in fulfilling these needs in the art. 
Specifically, this invention provides a device for measuring the force 
required to break a tablet, wherein the device comprises a tablet holding 
means comprising a base, a tablet splitting edge in the base and an area 
for holding a tablet in an inclined cantilevered position such that at 
least a portion of the cantilevered segment of the tablet extends over the 
tablet splitting edge. Means are provided for exerting a force 
substantially normal to a portion of the cantilevered segment of the 
tablet extending over the splitting edge to thereby create a moment of 
force about the tablet splitting edge sufficient to break the tablet. The 
device includes means for measuring the force required to break the 
tablet. 
The device of this invention thus not only measures the force required to 
break a tablet, but also gives a measure that is representative of the 
force required for a human to break a similar tablet. As will be apparent 
from the description that follows, the device of the invention is simple 
to operate and can be adapted for use with a variety of different size 
tablets.

DETAILED DESCRIPTION 
Referring to FIG. 1, it will be seen that the device comprises a tablet 
holding means 1 comprising base 2 having a top surface 3 and an area 4 for 
supporting a bolus tablet 5 such that a portion of the tablet extends 
beyond the top surface 3. More particularly, the tablet 5 is held in an 
inclined, cantilevered position with at least a portion of the 
cantilevered segment of the tablet extending over a tablet splitting edge 
6. The tablet splitting edge 6 is contiguous with the tablet holding area 
4 and these elements are unitary with the base 2 of the tablet holding 
means 1. 
Tablet holding means 1 is positioned on a substantially flat plate 7 on 
support members 8 and 9. Underneath plate 7 are strain gauges 10 and 11, 
which are connected to an indicating device (not shown). 
Provided above the tablet holding means 1 are means for exerting a force 
substantially normal to the portion of the cantilevered segment of the 
tablet 5 extending over the splitting edge 6. The means for exerting the 
force comprises a platen 12 rigidly secured to a substantially horizontal 
arm 13, which can be driven upwardly and downwardly over the threads of 
screws 14 and 15. 
The screws 14 and 15 can be rotated at constant rate. As the platen 12 
approaches tablet 5 in the tablet holding means 1, the platen will 
eventually contact the tablet. The force applied to tablet 5 via platen 12 
has a component F substantially perpendicular to the diameter 16 of the 
tablet 5. As depicted in FIG. 1, surface 17 of tablet 5 is parallel to the 
diameter 16. Continued application of force on the tablet 5 will result in 
a statically determinant system, and if sufficient force is applied, the 
tablet 5 will break. 
When the force F is applied to tablet 5, a moment of force is thereby 
created about the splitting edge 6, and this moment of force is sufficient 
to break the tablet 5 into two pieces, one piece being that in the tablet 
holding area 4 and the other piece corresponding to the portion extending 
over the tablet splitting edge 6. As depicted in FIG. 1, the tablet 
splitting edge 6 is below the tablet 5, and when the tablet is broken, the 
broken portion (corresponding to the cantilevered segment) will rest on 
surface 19 of tablet holding means 1 and will be below the top surface 3. 
Force F in FIG. 1 applied to surface 17 of tablet 5 proximate the outer 
edge 18 of the tablet is the only force that needs to be applied to 
cleanly break the tablet. For this reason, the force F can be termed the 
"breaking force". It is not necessary to apply forces along the remaining 
portions of the surface 17; such forces would tend to form compressive 
stresses and cause the tablet to crumble. The breaking force is alone 
sufficient to cause the tablet to snap. 
The breaking force can be determined by any suitable load measuring device. 
The measurement of loads by mechanical, electrical and optical principles 
is well known. An electrical resistance strain gauge, such as a metallic 
wire or semiconductor, is shown in FIG. 1. The strain gauges can be 
connected to a Wheatstone bridge circuit coupled to a meter via a suitable 
amplifier circuit. Such devices are commercially available. By calibrating 
the device against known standards, the breaking force can be simply 
measured. 
The tablet holding means 1 of FIG. 1 is shown in greater detail in FIG. 2. 
It will be seen that the tablet holding means 1 comprises base 2, tablet 
splitting edge 6 and area 4 for holding the tablet in position. A rigid 
tablet restraining arm 20 unitary with the base 2 prevents upward movement 
of the tablet when the breaking force is exerted proximate the outer edge 
18 (FIG. 1) of the tablet. The breaking force is balanced by a force 
exerted on the other extremity of the tablet by the tablet restraining arm 
20. Thus, forces can be exerted only at the extremities of the tablet to 
obtain the maximum moment of force about the splitting edge. The tablet 
splitting edge 6 forms a protrusion in the tablet holding area 4. 
Preferably, the tablet splitting edge 6 has a width substantially 
corresponding to the width of the tablet where the tablet is to be broken. 
The construction of another tablet holding means for use in the invention 
is shown in detail in FIGS. 3 and 4. Referring to these Figures, the 
tablet holding means 1 has a base 2, a top surface 3 and an area 4 for 
holding the tablet. The holding area 4 comprises an elongated opening or 
slot of substantially constant cross-sectional area throughout its width 
in the top surface 3 of the base 2. The area 4 extends from side to side 
of base 2. The tablet holding means 1 includes an area 21, which defines a 
cavity for receiving the broken portion of tablet 5. 
It will be appreciated that the tablet holding means can be adapted to 
accommodate tablets of different dimensions. For instance, the tablet 
holding means 1 can be made to accommodate tablets of different size by 
altering the depth (d) or the width (w) or both the depth and the width of 
tablet holding area 4 (see FIG. 4). The tablet holding means of FIg. 3 is 
preferred for use with small tablets, such as tablets having a length or 
diameter of about 50 to about 200 mm. The tablet holding means of FIG. 2 
is suitable for use with larger tablets, such as tablets having a length 
or diameter of about 200 to about 700 mm. The device of this invention can 
be used with tablets having a round, oblong, capsule or similar shape. 
Another device of the invention for measuring tablet breaking force is 
shown in FIG. 5. The device depicted is a modified Schleuniger 
(Switzerland) tablet hardness tester. The device comprises a powerized jaw 
23 driven by a motor 24 via rack 25, pinion 26 and transmission 27. 
As depicted in FIG. 5, a tablet 5 is positioned in a tablet holding means 1 
on powerized jaw 23. Tablet holding means 1 in FIG. 5 is the same as the 
tablet holding means 1 shown in FIGS. 3 and 4. In FIG. 5, the tablet 
holding means of FIG. 3 is positioned on its side opposite side 22 in FIG. 
3, with the tablet in the position shown. 
Opposite the tablet 5 is a measuring jaw 28 connected to a counterweight 29 
via thrust bearings 30 and 31 and linkages 32, 33, 34. A calibration 
weight 35 is provided for calibrating the device. 
The powerized jaw 23 driven by the motor 24 presses the tablet 5 against 
the measuring jaw 28 connected to the counterweight 29. A wire cord 36 is 
attached to counterweight 29 and travels over pulleys 37, 38 and 39. 
Attached to the wire cord 36 is a drag contact 40, which moves as the wire 
cord 36 moves. As drag contact 40 moves to the right, it contacts a 
pointer 41, which shows the force applied to the tablet 5 on a linear 
scale 42. 
When the tablet 5 breaks, the contact between drag contact 40 and pointer 
41 is interrupted. The motor 24 returns the powerized jaw 23 to its 
initial position. The pointer 41 remains adjacent the scale 42 to indicate 
the breaking force. At the start of the next test, the pointer 41 is first 
returned to its zero position by reset motor 43 via an electromagnetic 
clutch 44, which drives pulley 45. Another wire cord 46 is threaded over 
pulley 45 and pulley 47. Pointer 41 is secured to wire cord 46. 
The devices depicted in FIGS. 1 and 5 can accommodate a variety of tablets 
of different size. The only modification that needs to be made is 
modification of the tablet holding means to accommodate the size of the 
tablet. As previously noted, this can be readily accomplished by altering 
the dimensions of the tablet holding area 4 and interchanging different 
tablet holding means in the device. 
The significance of the broken tablet receiving area 21 (FIG. 3) will also 
be appreciated from the device shown in FIG. 5. When the tablet 5 is 
broken, the broken portion corresponding to the cantilevered segment falls 
into the area 21 free of the measuring jaw 28. The broken portions of the 
tablet do not interfere with further movement of machine elements or 
operation of the machine and can be readily removed when the machine cycle 
is completed. 
As depicted in the Figures, the tablet splitting edge 6 is a straight, 
stationary edge formed from part of the base 2 of the tablet holding means 
1. It is to be understood that the tablet splitting edge could also be a 
knife or blade installed in the base 2, but this embodiment is less 
preferred because additional assembly is reqired. Also, the tablet 
splitting edge could be serrated or located at a variety of distances from 
the top surface 3, provided that the tablet was adequately supported. 
The tablet is held in the tablet holding means in an inclined, cantilevered 
position with at least a portion of the cantilevered segment of the tablet 
extending over the tablet splitting edge. In the tablet holding means 
shown in FIG. 3, the outer edge 18 of tablet 5 is perpendicular to the 
diameter 16 of the tablet, which makes an angle (.alpha.) with the 
vertical equal to about 45.degree.. The corresponding angle for the tablet 
shown in the tablet holding means 1 in FIG. 1 is about 70.degree.. 
Typically, the angle (.alpha.) will be in the range of about 10.degree. to 
about 85.degree.. Preferably, this angle will be about 45.degree. to about 
75.degree.. For small tablets the angle (.alpha.) will typically be about 
45.degree. to about 85.degree. and for larger tablets about 10.degree. up 
to about 45.degree.. 
It is not necessary that the entire portion of the tablet to be broken 
extend beyond the top surface 3 of the tablet holding means 1. In fact, it 
is not necessary that any portion of the cantilevered segment of the 
tablet extend beyond the top surface, provided that the tablet breaking 
means, such as measuring jaw 28 in FIG. 5, is sufficiently offset so that 
the top surface does not obstruct movement of the tablet breaking means. 
The tablet breaking device of this invention makes it possible to evenly 
break tablets without crushing the tablet or causing the tablet to 
crumble. In addition, the breaking force measured is representative of the 
force required for a human to break a similar tablet. The device of this 
invention can be adapted to breaking tablets having a variety of sizes.