US3842925A - Device for raising weights in precision balances - Google Patents

Abstract

Device for raising weights in precision balances, such as analytical balances, in which a number of weights from the smallest to the largest are disposed substantially in a single plane and are made associated with at least two pusher raising elements mobile in a direction substantially orthogonal to the plane of the weights, the pusher raising elements being raised by programmed operating means including rotatable annular disc members and cam means provided thereon. The disc members are rotated by acting on the weighing control members of the balance.

Description

United States Patent 1 1 1111 3,842,925 Crespi 1 1 Oct. 22, 1974 [5 DEVICE FOR RAISING WEIGHTS IN 3,004,618 l0/l96i Meier 177/248 PRECISION BALANCES 3,026,954 3/1962 Appius 177/248 Carlo Crespi, Via Sordello 10. Milan, Italy Filed: Oct. 3, 1972 Appl. No.: 294,736

Inventor:

Foreign Application Priority Data Oct. 5. 1971 Italy 53269 References Cited UNITED STATES PATENTS 9/1956 Mettler 177/191 8/1960 Rapp ..177/203 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Vit W. Miska Attorney, Agent, or FirmGuido Modiano; Dr. Albert Josif [57] ABSTRACT Device for raising weights in precision balances. such as analytical balances, in which a number of weights from the smallest to the largest are disposed substantially in a single plane and are made associated with at least two pusher raising elements mobile in a direction substantially orthogonal to the plane of the weights, the pusher raising elements being raised by programmed operating means including rotatable annular disc members and cam means provided thereon. The disc members are rotated by acting on the weighing control members of the balance.

6 Claims, 9 Drawing Figures DEVICE FOR RAISING WEIGHTS IN PRECISION BALANCES BACKGROUND OF THE INVENTION The present invention relates to a device for raising and lowering weights in precision balances.

Precision balances, for example analytical balances, comprise a certain number of weights suspended at one end of the balance arm and a counterweight disposed at the opposite end of the arm, in such a manner as to exactly balance the balance. During the act of weighing, after having disposed the mass to be weighed on the plate lying below the weights and the balance has been thrown out of balance a number of weights are raised equivalent to the weight placed on the plate so as to again balance the balance. This operation is carried commonly out by hooks controlled by levers, which take each weight and raise it so that it no longer bears on the arm of the balance. A set of knobs is provided for controlling the levers, and their rotation causes movement of the levers by the action of corresponding means such as cams etc.

As the sensitivityof the balance increases, i.e., as the number of significant figures of weight determinable by the balance increases, the total number of weights also increases, these having then to be disposed in a number of groups sufficiently separated in order to enable the hooks and levers to correctly operate without interference.

The weights are hence disposed along a number of axes or horizontal planes one below the other, so as to limit the number of weights in each plane and make possible the raising operations for all weights from the mechanical point of view.

In the case of precision balances this arrangement, which is universally adopted, limits the sensitivity of the balance and introduces a factor of uncertainty and error, which become more significant as the precision of the balance increases.

When weighings are required to the order of four or five decimal places it becomes necessary also to consider the influence of atmospheric pressure at the various heights at which the weights are disposed.

The weights, calibrated exactly under the same conditions, no longer rigorously give the same value if disposed at different heights and this obviously influences the weighing precision to an extent which cannot be previously determined for each weight, and it is thus not possible to give an exact correction factor for correcting the weighing each time. This means that even the most sensitive balances always have a certain tolerance, even though small, which is imputable to this fact.

To this must be added the mechanical complexity of the system for raising the weights when these exist in great number and have to be disposed on a number of planes, and the fact that the weight is not raised perfectly vertically as is desirable, but through a certain are because of the fact that the levers are necessarily pivoted at a fixed fulcrum of the balance.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the aforementioned disadvantages of known precision balances by providing a device for raising the weights which firstly introduces no possibility of error in weighing, even in the case of extremely small weighings, and

furthermore leads to a considerable reduction, for like numbers of weights, in the overall bulk of these latter and simplification of the means for raising the weights.

Another object of the invention is to provide a device easily installed on precision balances and of durable operation.

These objects are attained by a device for raising weights in precision balances in which all the weights from the smallest to the largest are disposed substantially in a single plane and are each associated with at least two pusher raising elements mobile in a direction substantially orthogonal to the plane of the weights, the pusher elements being raised by programmed operating means associated respectively with the weighing control members of the balance.

BRIEF DESCRIPTION OF THE DRAWINGS Further particulars and characteristics of the invention will be more evident from the following detailed description of a preferred embodiment of the invention, illustrated by way of example in the accompanying drawings in which:

FIG. 1 is a diagrammatic lateral view of a precision balance to which the device of the invention is applied;

FIG. 2 is a partially exploded view of the device of the invention;

FIG. 3 is a view from above of the balance of FIG. 1 without the cover;

FIG. 4 is a plan view of the means for the programmed raising of the weights;

FIG. 5 is a section on the line VV of FIG. 4',

FIG. 6 is a part of the support for the weights;

FIG. 7 shows a detail on an enlarged scale of the pusher elements for raising the weights;

FIG. 8 is a lateral view of the clamping device for the means for the programmed raising of the weights; and

FIG. 9 shows a detail of the balance arm.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the example considered here the device 1 according to the invention is imagined applied to an analytical balance which in known manner comprises at its lower front part the compartment with the weighing plate 2 and in its upper part the actual members of the balance.

The balance beam 3 is supported through the central fulcrum 4 by the column 5 and is provided with the counterweight 6 and air damper 7 at one end and the.

group of annular weights 8 at the other end, from which the plate 2 is also suspended. The groups of weights, which will be described in detail hereinafter, is suspended from the balance beam 3 by way of the rods 9 fixed to the cross member 10, which comprises a lower a lapped surface for support on the block 11, which is provided as a lateral fulcrum on the balance beam 3 at the same distance from the fulcrum 4 as the counterweight 6. The weighing operation is carried out by manually operable control means such as knobs 12, 12a and 13, 130 by way of appropriate transmission devices 14 which will be described in greater detail hereinafter.

According to the invention all the annular weights, from the smallest to the largest, are disposed concentrically in the same horizontal plane, and supported in this plane by the arms 15 disposed at one to the other to constitute the support member for the weights. The

arms 15 comprise notches 16 of a number corresponding to the number of the weights and ofa suitable shape and size for seating the weight according to its size and they converge at the central body 18, to which the rods 9 are fixed, The weights are disposed in increasing order from the centre and in the example under consideration they are the following: two weights of 100 mg, one of 200 mg, one of 500 mg, two weights of l g, one of 2 g, one of g, two weights of g, one of 20 g, one of 50 g, and one weight of 100 g. in this manner there is a total of 13 weights whose sum total is I99.900 g. It is to be understood however that their number and value could be different.

Immediately below the plane of the weights but free from it, the device 1 comprises the pusher elements and the operating means for the programmed raising of the weights, indicated overall by the reference numeral 20. More precisely the device 1 comprises a base 21 of cylindrical form, to whose lateral surface 22 are fixed at 90 one to the other the supports 23, provided at their free end with a notch 24 in which is clasped the corresponding end of the transverse stop bars 25, whose form is visible inFlG. 5 and against which the raised weights engage. The crosspieces 26 and 27 are fixed to the supports 23 below the bars and define guiding means in which pins 28 and 29 are slidable in a direction orthogonal to the plane of the weights 8. The pins 28 and 29 constitute the pusher elements for raising the weights and are distributed in such a manner that each pair of diametrically opposing pins supports a single annular weight, the pairs being alternated between one crosspiece and the other as passage is made from one weight to the next. The means for the programmed operation of the pins comprise rotatable annular disc members or programming plates 30, 31, 32 and 33, which each comprise on their upper face as series of profiles or cams 34 disposed according to a precise programme, and on their lower face operating means including a respective annular too thing 35 which meshes with three gearwheels 36, disposed at 120 one to the other. One of the gearwheels 36 of each plate is fixed rigidly to a shaft 37 which emerges from the lateral surface 22 of the base 21 and comprises a bevel gear 38, operatively connected to the knobs 12, 12a and 13, 13a. The other gearwheels 36 of each plate are fixed to respective shafts housed idly in the lateral surface 22 and in the central part 40 of the base 21 and serve exclusively as a support for the programming plates, which thus also lie in a single plane as the weights 8. The disposition of the various gearwheels below the programming plates, and of all other toothed wheels for the operation of the programming plates, is shown in FIG. 3 in which the details above the plates and the weights have been omitted. The entire device 1 is removably mounted on the shelf 41 of the balance.

The internal programming plates 31, 32 33 have ten cam profiles or portions which are repeated identically over the angular development of each of them. The most external plate 30 has instead a different profile and comprises only four cam portions. For this reason only the form of the profiles ofthe plates 31 and 30 will be described hereinafter.

In the example described and shown, with each of the internal programming plates 31, 32 and 33 are associated four weights, multiples of 10 of the two weights of I00 mg, of that of 200 mg and of that of 500 mg. With this values of weights it is possible, as is known, to define an entire weight decade. With the external plate 30 is associated a single weight of 100 g. One turn of the programming plates 31, 32 and 33 corresponds to an entire weighing are from 1 to 9 100-900, [0-90) plus the position 0, so as to obtain all the weight values which are multiples of 100 mg. in order to obtain this each of the plates 31, 32 and 33 has the profiles 34 disposed on five concentric circumferences, the profiles being diametrically symmetrical in pairs. The plate 31 has thus two sections 310 acting on the pins situated below the first weight of IO g, two sections 311) and two sections 310 acting on the pins situated below the second weight of 10 g, two sections 31d acting on the pins corresponding to the weight of 20 g and finally a cam portion 31c and a cam portion 31f, both for raising the weight of 50 g, but situated on different circumferences. This latter weight must in fact be held lowered for one half of a turn and raised for the other half, so that a single cam acting on diametrically opposed pins could not cause the pins to be either both raised or both lowered. There are consequently two separate cams acting each over one half of a turn on one pin so as to simultaneously carry out the same operation. To this end one of the relative pins has its upper end eccentric with respect to its lower end (FIG. 7).

The external programming plate 30 comprises two sections 30b and 30c relative to the weight of 100 g, disposed angularly distanced as the sections 311) and 310 of the plate 31. The drawings show also the corresponding sections 32a, 32b, 32c, 32d, 32e and 32f and the sections 33a, 33b, 33c, 33d, 33e and 33fof the profiles of the plates 32 and 33.

The length of the individual sections of the profiles is such that for each angle of rotation of 36 of the plate, an increase in weight of one relative unit is obtained, in the succession described hereinafter.

Considering for example the plate 31 and the position in which all the pins are lowered, with a first rotation of 36 will correspond the intervention of the section 310 and the raising of the pins 29 of the first weight of 10 g. During a further rotation of 36 the section 31a will remain active and the section 311) will intervene and cause the raising of the second l0 g weight by the pins 28, arranged at 90 to those which keep the first 10 g weight raised. There is thus a total of 20 g raised. During a further rotation of 36 the section 31b is no longer active and the second l0 g weight descends, whereas the first is kept raised by the section 310, and the 20 g weight is raised by the intervention of the section 31d. There is now a total of 30 g raised. On rotation through a further 36 the section 31c intervenes, and raises the second l0 g weight, while the 10 and 20 g weights are kept raised by the remaining sections 310 and 31d. There is now a total of 40g. On a further rotation of 36 all the weights raised up to now by the sections 310, 31c and 31d descend and the sections 3le and 31f intervene, and simultaneously raise the two pins of the 50 g weight. There is now a total of 50 g. Proceeding further, as the profiles are diametrically symmetrical and up to this point one half of a turn has been made, then for every 36 of rotation the previous operations will be repeated, with the difference that the 50 g weight will always remain raised. Thus 60 g, g, g and g are obtained in succession, after which the last rotation of 36 will return all the pins to rest and cause all the weights to descend.

It is evident that the same phases will occur by operating the plates 32 and 33, but in this case the weights will proceed from 100 mg to 900 mg and from 1 g to l0 g respectively.

The last weight of 100 g requires only two positions, one raised and one lowered, and hence the profiles of the external plate 30 comprise in substance two sections 30b and 30c separated by 72, so as to give a position of 0 between two raising positions.

The weights and the positions of the plates and pins shown in the drawings are those relative to a hypothetical weighing of 170.600 g.

In all these operations the raised weights are made to lightly touch the transverse bars 25 with a slight pres sure.

To this end the pins are advantageously composed (FIG. 7) of a lower shank 42 rigid with a body 43 of substantially cup form guided in a corresponding seat 44 in the cross bars 26 and 27 respectively, and an upper shank 45 mobile in the body 43 and supported by a spring 46 inserted in the body 43. One of the two pins for raising weights which are multiples of 500 mg is eccentric, as stated, and it comprise two shanks 42 and 45 olT-centre in the body 43a.

The presence of the spring enables the efiect of the impact of the weights against the bars 25, which could damage the weights, to be dampened, and simultaneously makes the operation of the programming plates more smooth. When the balance is at rest the weights supported by the arms are all engaged with the bars, even if the pins are all lowered.

Rotation of the programming plates by the bevel gears 36 takes place by way of the knobs 12, 12a and 13, 130, each of which (FIG. 3) is associated with one ofthe programming plates. The knobs l2 and 13 act by way of the gearwheels 47 and 48 rigid with the shafts on which the knobs are fixed, and the gearwheels indicated generally by the reference numerals 49 and 50 on the bevel gears 36 of the plate 33 and 30, respectively. The knobs 12a and 13a act by way of the gearwheels 51 and 52, rotably rigid with these knobs, on the gearwheel assemblies indicated generally by the reference numeral 53 and 54, respectively, with which the remaining plates 31 and 32 are associated. Advantageously snap action devices are provided consisting of notched wheels 55 and springs 56 engaged with these notches for the rotation of the knobs through a predetermined angle and their exact arrest in each weighing position. The transmission 47-54 is so calculated in the ratios of the different gearwheels that with one turn of each programming plate there corresponds one turn of the corresponding knob, so that the snap action devices act on each 36 of rotation both of the knobs and of the programming plates, so defining without any possibility oferror the exact position in which each weight is perfectly raised or lowered and not in an intermediate position. With the knobs are associated circular scales numbered from 0 to 9, by which it is possible to directly read the weighing value on a suitable panel at the front of the balance. The scales are one within the other on each side, so as to give the values in the exact order of reading from left to right.

Each weighing position can be locked by the locking device shown in FIG. 8. This is arranged on the shelf4l of the balance in a position corresponding with a cavity 57 in the base 21 and comprises four pins 58, one under each plate, designed to enter relative dead holes 58a provided under the plates at a distance one from the other of 36, starting from a predetermined position. The pins 58 are fixed to a plate support 59 which is mobile above the bracket 60, fixed to the shelf 41 of the balance, and comprises guide pins 61 passing through suitable holes 62 in the bracket 60. For raising the pins 58 a lever 63 is provided pivoted at 64 on the shelf 41 of the balance, and acts on the wheel 65 carried by the rod 66 screwed into the plate support 59 and guided in the sleeve 67 fixed to the bracket 60. The springs 68, arranged between the bracket 60 and enlarged end of the pins 61, remove the pins 58 from their engagement in the dead holes 58a of the programming plates. Control of the locking device is by the rod 69 operating connected to the lever 70 disposed in the lower front part of the balance.

For further increasing the sensitivity of the balance, an optical system may be provided for reading the last figures of the weighing, and comprising (FIG. 3) a graduated scale disposed on the arm 3 in axis with the luminous ray produced by the lamp 73, and a fixed mirror 76 for reflecting the luminous ray coming from lamp 73 through lenses 74 and 75 on to a vernier scale provided on a suitable panel in the upper front part of v the balance. With this fixed mirror and vernier system the possibility of errors in reading the weighing is considerably reduced.

From the description given it can be understood that with the device according to the invention the objects initially stated are attained. In particular the disposition of the weights eliminates with certainty any error due to pressure differences and, together with the disposition of the entire control assembly, considerably reduces the overall size of the device.

Various modifications may be made to the device described within the inventive concept, without leaving the scope of the inventive idea. Thus the device may be applied to types of precision balances different to that illustrated and wherever greater weighing precision and lower constructional cost is required, for example in the field of technical balances, and furthermore the various control means and means for raising the weights may be modified according to requirements. In an advantageous solution, a control system is provided having all pins rigid with one plate, which is raised according to a programme by cams suitably set to raise the various weights in succession. In this case a fixed programming plate is provided, in which a number of holes are disposed in accordance with a set pro gramme, so that the underlying plate carrying the pins brings a certain number of pins under the relative holes in the fixed programming plate for each section of rotation, and when raised pushes the pins into these holes, so raising the relative weights, while the pins not aligned with the holes remain inactive.

I claim:

I. A device for raising and lowering the weights in precision balances of the type having a balance beam, a support member suspended at one end of said balance beam, a plurality of annular weights supported by said support member concentrically to each other in a substantially horiziontal plane, and manually operable control means for controlling the raising and lowering of said weights, the device comprising a base for removable connection to said balance below said support member, guiding means provided over said base and extending below said weights substantially radially thereto, a plurality of pusher elements including pins slidable within said guiding means substantially perpen dicularly to the plane of said weights for raising and lowering said weights, means for operating said pins including rotatable annular disc members arranged concentrically to each other in the same plane below said guiding means and having an upper face provided with cam means for engaging said pins and a lower face provided with operating means for independent rotation of said disc members, said operating means being operatively connected to said manually operable control means of the balance, whereby operation of said control means causes rotation of said disc members and raising and lowering of said weights according to a program defined by said cam means.

2. A device as claimed in claim 1, wherein said operating means for independent rotation of said disc mem bers comprise an annular toothing provided on the lower face of each of said disc members concentrically thereto, each of said toothings being operatively connected to said manually operable control means of the balance by means of gearing.

3. A device as claimed in claim 1, wherein with at least one of said disc members there are associated four weigths having respective values capable of defining an entire weight decade, and wherein said cam means are arranged on the upper face of said disc members along concentric annular paths, said cam means having cam portions located along said paths at angularly spaced of 36 or multiples thereof, whereby after one complete turn of said disc member all the weights of the entire weights decade have been raised.

4. A device as claimed in claim I, wherein said guiding means comprise two crosspieces arranged at right angles to each other in a substantially horizontal plane above said disc members, said crosspieces each having pairs of through bores for receiving respective pairs of said pins, each pair of said pins engaging one of said weights at diametrically opposite points, the pairs of pins relative to adjacent weights being disposed alternatively in the one and the other of said crosspieces.

5. A device as claimed in claim 1, wherein at least one of said disc members has an external cam comprising two cam portions arranged opposite to each other along annular concentric pathes of slightly different radii and each extending for a half of its circumference, with each of said cam portions being associated one pin comprising an upper and a lower shank, the shanks of one of said pins being coaxial to each other and the shanks of the other of said pins being off-centered, whereby the said upper shank engages the corresponding one of said annular weights and the said lower shank engages the corresponding one of said two cam portions.

6. A device as claimed in claim 5, further comprising a spring interposed between said upper and said lower shank.

Claims (6)

1. A device for raising and lowering the weights in precision balances of the type having a balance beam, a support member suspended at one end of said balance beam, a plurality of annular weights supported by said support member concentrically to each other in a substantially horiziontal plane, and manually operable control means for controlling the raising and lowering of said weights, the device comprising a base for removable connection to said balance below said support member, guiding means provided over said base and extending below said weights substantially radially thereto, a plurality of pusher elements including pins slidable within said guiding means substantially perpendicularly to the plane of said weights for raising and lowering said weights, means for operating said pins including rotatable annular disc members arranged concentrically to each other in the same plane below said guiding means and having an upper face provided with cam means for engaging said pins and a lower face provided with operating means for independent rotation of said disc members, said operating means being operatively connected to said manually operable control means of the balance, whereby operation of said control means causes rotation of said disc members and raising and lowering of said weights according to a program defined by said cam means.

2. A device as claimed in claim 1, wherein said operating means for independent rotation of said disc members comprise an annular toothing provided on the lower face of each of said disc members concentrically thereto, each of said toothings being operatively connected to said manually operable control means of the balance by means of gearing.

3. A device as claimed in claim 1, wherein with at least one of said disc members there are associated four weigths having respective values capable of defining an entire weight decade, and wherein said cam means are arranged on the upper face of said disc members along concentric annular paths, said cam means having cam portions located along said paths at angularly spaced of 36* or multiples thereof, whereby after one complete turn of said disc member all the weights of the entire weights decade have been raised.

4. A device as claimed in claim 1, wherein said guiding means comprise two crosspieces arranged at right angLes to each other in a substantially horizontal plane above said disc members, said crosspieces each having pairs of through bores for receiving respective pairs of said pins, each pair of said pins engaging one of said weights at diametrically opposite points, the pairs of pins relative to adjacent weights being disposed alternatively in the one and the other of said crosspieces.

5. A device as claimed in claim 1, wherein at least one of said disc members has an external cam comprising two cam portions arranged opposite to each other along annular concentric pathes of slightly different radii and each extending for a half of its circumference, with each of said cam portions being associated one pin comprising an upper and a lower shank, the shanks of one of said pins being coaxial to each other and the shanks of the other of said pins being off-centered, whereby the said upper shank engages the corresponding one of said annular weights and the said lower shank engages the corresponding one of said two cam portions.

6. A device as claimed in claim 5, further comprising a spring interposed between said upper and said lower shank.

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