GB2120797A - Dynamometric pliers - Google Patents

Abstract

Dynamometric pliers intended more particularly for measuring the crushing strength of tablets, granules or the like, comprise essentially a force pick-up incorporated in one of the jaws (2) and an electronic circuit (7) for storing the maximum value of the reaction exerted by the article to be tested which is disposed between the jaws (2, 3) during the crushing test. Thus, the value displayed by the digital display device (6) corresponds directly to the force necessary for breaking up the product. The apparatus is useful notably in pharmaceutical and agricultural industries. <IMAGE>

Description

SPECIFICATION Dynamometric pliers The present invention relates to dynamometric pliers ortorquetongs ofthetype intended notably for measuring the forces necessary for crushing tablets, granules and the like. This invention is applicable notably in the field of pharmaceutics, agriculture and various industries connected thereto, for testing products in the form oftablets and granules.

One of the various mechanical properties required for tablets and the like is crush resistance. This specific parameter is measured by exerting an increasing force on the tablet until it is crushed, the maximum force detected just before the tablet breaks up corresponding to the crush resistance.

Various devices have already been proposed for measuring the crush resistance oftablets; these devices falling into two categories; portable apparatus and laboratory apparatus.

Among the portable apparatus the most widely used one is a spring-type dynamometer in which the object to be tested is compressed indirectly by using a gauged intermediate spring. By measuring on scales the degree of compression ofthe gauged spring, it is possible to determine the force exerted on the tablet.

However, this crush resistance measurement is rather unreliable since one must 'feel'the moment when the tablet breaks up and read on the scale position the effort impressed on the spring exactly at that moment.

Apparatus of this kind is delicate to handle, its precision is doubtful and furthermore the measuring time isvery long sincethespring is compressed by means 6f a screw.

In the category of laboratory apparatus various principles are implemented, inter alia, notably, motorized apparatus also utilizing a gauged spring for measuring the efforts impressed on the tablets. This type of apparatus is objectionable notably because it is heavyand cumbersome, and provides only a relatively narrow measuring range.

According to the present invention there is provided dynamometric pliers, notably for measuring the crush resistance oftablets, granules and the like, which comprise two jaws between which a productto be tested is disposed, at least one of said jaws being actuatable by means of a handle pivoted to the body of the pliers, the results ofthe measurement being displayed by a digital display device, characterised in that means are provided for measuring the maximal reaction force exerted by the product during the crushing thereof against at least one of the pliers' Jaws.

It is an object of the present invention to provide an improved type of self-contained dynamometric pliers having moderate over-all dimensions and providing a direct display of the crushing force exerted thereby.

Thus, handling of the pliers is extremely easy and reading errors are definitely eliminated.

It is another object ofthe present invention to provide a pair of dynamometric pliers providing for a relatively wide range of measurements and therefore perfectly adapted for measuring the crush resistance oftablets having different hardness values without requiring any preliminary adjustment.

Though the device ofthe present invention is battery-operated, it can be used for relatively long time periods since it comprises only low powerconsumption electronic components.

Moreover, the relative position ofthe jaws ofthe dynamometric pliers may be modified and adapted to the size and particular geometry of tablets of all types and shapes.

The dynamometric pliers of the present invention are useful in many other applications such as the measurement of the hardness of powders intended for use in the manufacture of sintered materials, controlling the shearing resisitance of pins, etc....

Other objects and advantages ofthe present invention will appear as thefollowing description proceeds with reference to the accompanying drawings, the description and drawings being given byway of illustration, not of limitation.

The invention will be better understood if reference is made to the description and drawings, in which: FIGURE lisa longitudinal section illustrating a preferred form of embodiment of the dynamometric pliers according to the present invention; FIGURE 2 is a detail sectional view showing on a larger scale the jaws of the pliers of Figure 1, and FIGURE 3 is a wiring diagram ofthe electronic circuitry for processing the signal delivered by the force pick-up.

The dynamometric pliers according to the present invention are intended for measuring effort and more particularly, in the case depicted herein for measuring the crushing force applied to tablets, granules, powders, etc....

However, this invention may easily be adapted for measuring the shearing resistance of pins and other similar objects, by simply adapting the jaws of the pliers to the object to be measured, which is within the ambit of skill of those conversantwith the art.

In the exemplary and preferred form of embodiment illustrated in Figure 1 the dynamometric pliers 1 comprise a pair of jaws 2,3 between which the object to be tested is disposed.

At least one of the jaws 2 is actuatable by means of a handle 4 pivoted to the body 5 of the apparatus 1 to move the jaws 2 and 3 towards each other and thus to crush a tablet or other object placed therebetween.

The crushing force is displayed upon a digital display device 6 provided on top ofthe body 5. Thus, the operator may read directlythe result ofthe test during the measurement. The dynamometric pliers 1 are portable and self-contained, so that it is particularly easy and convenient to use them in most circumst- ances.

The dynamometric pliers 1 comprise means for measuring the maximal reaction force exerted by the tablet during the crushing thereof, on at least one of the jaws 2. Thus, since it is the maximal force that is measured,the latter corresponds exactly to the crush resistanceofthetablet.

Moreover, this maximal force is memorized and displayed, so thatthe operator can read the value deliberately, since the display is a lasting one.

The measuring means comprise a force pick-up element incorporated in one of the jaws 2, where it is subjected to the reaction force or resistance of the tablet.The measuring means further comprise an electronic circuit7 with memory meansforstoring the maximal value of the reaction force exerted by the tablet during the crushing operation. This electronic circuit, like the display means, is disposed inside the body 5 of the pliers 1. An electronic circuit displays on said display device 6 the value converted into force units stored in the electronic memory circuit.

Before making another measurement, the memory must be cleared or at least re-initialized, according to the preferred form of embodiment of the invention, this zeroing of the memory resulting from the opening of the handle 4 and therefore ofjaws 2 and 3. Thus, the operator is not required to perform any particular manoeuvre for resetting the device; however, as long as the operator keeps the pliers closed, the crushing force is displayed by the display device 6.

The jaw2 has the configuration of a slidably guided piston ofwhichthe axial movements are produced by actuating the handle 4 pivoted about a pin 8 disposed in the body 5 ofthe pliers, the handle 4 acting as a lever for moving the movable jaw 2 towards the fixed jaw 3.

The return movement of handle may be obtained automaticallyfor example by means of a spring 9, another spring 10 urging the jaw 2 to its open position.

The rod 11 guiding the jaw 2 may advantageously actuate at the end of its stroke a switch 12 of which one function consists in re-initializing or zeroing the memory circuit.

The otherjaw 3 constitutes an insert fitted in the body 5 ofthe pliers 1 so that it can easily be replaced with anotherjaw according to the particular shape and size ofthe product to be tested; Moreover, the distance between the jaws 2 and 3, when the pliers are open, can be adjusted by means of a knurled wheel 13 controlling the axial position of the fixed jaw 3.

Figure 2 illustrates diagrammatically in detail the force pick-up incorporated in the movable jaw 2. This jaw 2 has the shape of a hollow piston enclosing a piezo-electric element 14. The piston 2 comprises a hollow base portion 15 and a jaw-forming insert 16 flexibly assembled therewith. Thus, the piezo-electric element 14 disposed within the hollow base portion 15 will receive integrallythe effort exerted on the jaw insert 16. The flexible mounting ofthe jaw insert 16 on the base portion 15 may be obtained for example by means of aflexible O-ring 17.

The voltage generated across the terminals ofthe piezo-electric element 14 when a pressure is exerted thereon may be picked up by conducting sheets 18 and 19 disposed on the front and rearfaces ofthe element. Sheet 18may for instance be insulated from the base portion 15 by interposing an insulating sheet 20 therebetween.

The voltage difference picked up by the conducting sheets 18 and 19 may be transmitted to the electronic circuit7 by means ofelectricwires 21 passing through an axial hole 22 formed in the rod 11 of piston 2.

Figure 3 illustrates the wiring diagram of the means utilized for processing the data received from the piezo-electric element 14 constituting the force pickup element.

In this example the piezo-electric element is a quartz button 14thevoltageofwhich isfed to the input of an operational amplifier 23, preferably of a type havinga high input impedance. In fact, this feature enables the operatorto perform slowly the crushing step without altering the measure as a consequence of a loss of load produced across the quartzterminals.

The operational amplifier23 isconnected as a maximum voltagethreshold detector. Consequently, the charge of capacitor 24 will correspond to the maximal voltage produced across the quartzterminals during the crushing operation, so that this force will be stored in the memory.

The other operational amplifier 25 connected as a unitary gain amplifier permits of delivering a voltage proportional to the voltage available across the terminals of capacitor 24 to an analogueldigital circuit (not shown) supplying display means showing a voltage value proportional to the maximal effort produced during thetest. Moreover, the apparatus may be calibrated by means of a potentiometer 26.

Aswitch 12 is connected across the terminals of capacitor 24 and actuated when the handle 4 of pliers 1 is returned to its open position for zeroing the memory.

To avoid any drift in the apparatus, which would result in a faulty measurement, a circuit connected in parallel with switch 12 will short-circuit the quartz button 14when the pliers are open, and a drift compensation circuit 27 will be substituted for the quartz button 14 across the quartzterminals.

Of course, various modifications may be made by those conversant with the art to the specific and preferredform of embodiment described herein with reference to the attached drawing without departing from the basic principles ofthe invention.

Thus, more particularly, the particular configuration ofthe dynamometric pliers described hereinabove makes the instrument particularly convenient for measuring the crush resistance of tablets. However, for measuring other forces, such as the shearing strength of pins, it is clearthat a different arreangementwoula be preferable.

Furthermore, the dynamometric pliers according to the present invention are also applicable to the pharmaceutic field of drinkable ampoules for measur ingtheforce necessaryfor breaking their ends.

Claims (11)

1. Dynamometric pliers, notably for measuring the crush resistance oftablets, granules and the like, which comprisetwojaws between which a productto be tested is disposed, at least one of said jaws being actuatable by means of a handlepivotedtothe body of the pliers, the results ofthe measurement being displayed by a digital display device, characterised in that means are provided for measuring the maximal reaction force exerted by the product during the crushing thereof against at leastone ofthe pliers' jaws.

2. Dynamometric pliers according to claim 1, characterisedinthatsaid means consist onthe one hand of a force pick-up device incorporated in one of said jaws and exposed to the reaction force of the tablet, and on the other hand of an electronic circuit for storing the value of the maximal reaction exerted by the tablet or the like during the crushing operation.

3. Dynamometric pliers according to claim 2, characterisedinthatthe electronic circuit displays on the display device the value converted into force units which is stored in said memory electronic circuit.

4. Dynamometric pliers according to claim 2 or 3, characterised in that said electronic circuit is reinitialized or zeroed when said handle and consequently said jaws are open.

5. Dynamometric pliers according to any preceding claim characterised in that one of the jaws consists of a hollow piston incorporating a piezo-electric element said piston comprising a hollow base portion and a jaw constituting a flexibly mounted insert permittingthetransmission ofthe effort to which said piezo-electric element is subjected.

6. Dynamometric pliersaccording to any preceding claim, characterised inthatthe distance between the jaws when open is adjustable.

7. Dynamometric pliers according to any preceding claim, characterised in that one of said jaws constitutesan interchangeable insert on said pliers.

8. Dynamometric pliers according to claim 2, characterised in that said force pick-up consists of a piezo-electric element, for example of quartz, and that said piezo-electric etement is short-circuited when the pliers are open.

9. Dynamometric pliers according to claim 8, characterised in that said electronic circuit for storing the maximal voltage generated acrosstheterminals of said piezo-electric element during the pliers operation has a high input impedance, and that drifts therein are compensated for.

10. Dynamometric pliers according to Claim 5, characterised in that said piston constituting the first jaw is moved in its axial direction i.e. towards the other jaw by a lever-forming portion of said handle.

11. Dynamometric pliers substantiallyas hereinb efore described with reference to the accompanying drawings.