US2812173A

US2812173A - Cyclical arrestment device for balances

Info

Publication number: US2812173A
Application number: US395578A
Authority: US
Inventors: Claridge Frederick Arthur; Hinton Norman Frank; Whitcroft Robert John
Original assignee: Stanton Instruments Ltd
Current assignee: Stanton Instruments Ltd
Priority date: 1957-06-05
Filing date: 1953-12-01
Publication date: 1957-11-05
Anticipated expiration: 1974-11-05

Description

F. A. CLARIDGE ETAL CYCLICAL ARRESTMEN'I DEVICE FOR BALANCES 2 Sheets-Sheet 1 Filed Dec. 1, 1953 Nov. 5, 1957 A. CLARIDGE ErAL 2,812,173

CYCLICAL ARRESTMENT DEVICE FOR BALANCES Filed D90. 1. 1953 2 Sheets-Sheet 2 Unitcd States Patent CYCLICAL ARRESTMENT DEVICE FOR BALANCES Frederick Arthur Claridge, Morden, Surrey, Norman Frank Hinton, Upper Norwoo'd, London, and Robert John Whitcroft, West Norwood, London, Engiand, assignors to Stanton Instruments Limited, London, England, a British company Application December 1, 1953, Serial No. 395,578 Claims priority, application Great Britain June 5, 1957 Claims. (Cl. 265-54) This invention relates to the construction and operation of precision or chemical knife edge balances, that is to say balances of the kind comprising a beam which is mounted by means of a knife edge and a plane, radius or'groove type bearing.

It is common practice when making balances of high precision which incorporate one or more knives and planes or similar bearing surfaces to arrange an arrestment mechanism which will relieve or remove the knives from contact with their appropriate bearings between usage. Such arrestment mechanisms take varying forms. A balance is said to be arrested when the freedom of movement is taken from the beam in either its loaded or unloaded state, that is its ability to make either deflection or pendulum type swing is prevented. This is accomplished by separation of the knife about which the beam deflects or swings from its bearing surface.

Generally the remaining knife or knives which carry the pan suspending pieces, pans and the loads are also relieved of their burdens by the same mechanism. For the purpose of this specification the words arrestment mechanism are used to denote any mechanism which relieves or separates all or some of the knives from their appropriate planes or bearings, or which clamps the beam in a fixed position.

A balance is said to be actioned when the reversed procedure is accomplished, that is the knives are allowed to contact their appropriate bearings and the balance has freedom of movement. This is normally accomplished by the same mechanism as arrestment either by its reversal or by continued movement in the same direction.

The details of such arrestment mechanisms admit a wide variety of forms. In some balances the beam is itself raised and lowered substantially. In others the beam, which being held in the fixed position by a bar or pair of pivoted bars, moves but slightly whilst the support bars themselves fall away. Occasionally the mechanism merely clamps or locks the beam without actual relief or separation of the knives from the bearing surfaces.

Such mechanisms have for their principal object the protection of the knife edges when the balance is not in use or during the placing or removal of a load. They are also designed, however, to ensure accuracy of reproducibility of the lines of contact between knives and planes or bearings. For this purpose a wide variety of adaptors are attached to the arrestment bars and beams so that each time the beam is arrested it will also be accurately located if any movement has occurred. The most common of these adaptors is represented by the well known system of three points arranged on vertical pillars from the arrestment bar which engage with a. cone, a V groove, and a plane attached to the underside of the beam.

It is well known that when a knife edge balance is allowed to remain in its action position for more than a few minutes, vibration and other external influences ICC such as draught, lack of perfect levelling and the like cause the knives of the balance to drift or move across or along the planes or bearings which they contact.

When there is a need for prolonged contact of the knives with the planes such as would be required in continuous or continuously recorded weighing with these balances, this movement not only renders it difficult to follow the deflection or oscillations of the beam with any follower type mechanism but also results ultimately in one or more of the knives reaching the extremity of the plane or bearing which it contacts when subsequent separation would cause permanent damage to the knife edge concerned.

For these reasons it has hitherto been considered to be impossible to use a knife edge precision balance for continuous weighing and various proposals have been made for avoiding the use of the conventional knife edge and plane in such circumstances. However such arrangements, which include wire suspensions and cross leaved springs, invariably result in loss of sensitivity and accuracy when compared with the traditional knife edge balance.

According to the present invention, a precision balance of the knife edge type and provided with arrestment mechanism as described above is adapted for use in continuous weighing by the provision of means which operate the arrestment mechanism at regular or irregular time intervals during the weighing process whereby the beam is relocated at each operation.

It is contemplated that the arrestment mechanism may be operated automatically at the required time intervals by any form of electrical, mechanical, thermal or hydraulic source of power, such as electric motors, turbines, clocks, electromagnetic mechanisms, spring or weight driven mechanisms with or without escapements, thermal and hydraulic mechanisms. The word operation is intended to include the complete arrestment and the further reloading or actioning of the balance whether by means of continuous movement of the mechanism in the same direction or by means of its reversal.

The purpose of operating the arrestment mechanism at known time intervals is to reposition the balance beam sufiieiently frequently before drift or movement has become significant. Thus the knives are recontacted frequently with their planes or bearing surfaces and thereby maintain the same relative position with one another, while the beam will show by its deflection a continuous weighing between each operation of the arrestment mechanism. By a follower mechanism of any form this continuous weighing may be translated into a continuous record on paper or film disturbed only by the actual operation of the automatic arrestment operating device, and such disturbances may constitute a valuable indication of time on the record if the operation is effected at accurately timed and regular intervals.

Such a system of operation need not interfere with normal hand operation of the arrestment mechanism, and balances arranged for operation in accordance with this invention may incorporate a device providing for hand or manual overriding operation.

In order that the invention may be clearly understood one form thereof will now be described with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of one form of precision balance,

Figure 1A is a fragmentary view of part of Figure 1,

Figure 2 is a section on the line II-II of Figure 1,

Figure 3 is an under plan view, and

Figures 4 and 5 are wiring diagrams of two alternative arrangements.

Referring now to Figure 1, there is shown as regards the upper part of this figure a knife-edge precision balance of conventional design, the arrangement comprising a beam 1 which is supported by an inverted knife edge 2 (see Figure 1A) secured therewith and which rests when the balance is actioned on a plane 3. This plane is supported on a plate 4 which is spaced by pillars 5 from a second plate 6 and this latter plate is secured on the top of a pillar 7.

f The

lower parts

8, 9 of opposite ends of the beam carry knife edges on which planes secured with the pan suspending pieces Ni, 11, rest.

When the balance is arrested these various knife edges are separated from their planes. In the balance shown this is effected as follows: The pillar 7 is formed with a central longitudinal aperture Within which is a rod 12. As will be described in greater detail below, this rod is movable vertically by means of a cam 13 which engages the lower end of the rod through a follower 14. The upper end of the rod 12 is secured to a platform 15 which is apertured to pass the pillars 5 and extends beneath the beam 1. This platform is provided at the centre of its front and back edges, as seen in Figure 1, with uprights 16 which are formed at their upper ends with V notches. These notches engage, when the rod 12 and platform 15 are lifted, a spindle which extends through the beam normal to its plane and thus lifts the beam to separate the knife edge 2 from the plane 3. In order to locate the beam one side of the spindle is formed with a groove which engages the sides of the V notch in the respective upright 16. two adjustable set screws 17 which engage the lower face of the

parts

8, 9 of the beam as the platform 15 is raised. The combined effect of these measures is that each time the balance is arrested the beam is accurately positioned so that each time the balance is actioned the knife edge 2 is returned to the identical position on its plane 3.

The arrestment mechanism also operates to remove the load from the knife edges carrying the pan suspending pieces and 11 and to position the respective planes on these knife edges. For this purpose the platform is provided with pairs of

pillars

18 and 19 the pointed ends of which engage one a V notch and the other a cone formed in the under face of the pan suspending pieces. The arrestment mechanism also includes plungers 20 which are raised to engage the pans 21 by cams 22 when the mechanism is operated.

The cams 22 and the cam 13 are carried on a shaft 23 which is mounted in bearings 24 on a plate 25 secured on the under side of the base of the balance. One end of this shaft extends through the case of the balance and is provided with a knob 26 so that the arrestment mechanism may be operated by hand as is the case in conventional knife edge balances. The other end of the shaft 23 carries a gear wheel 27 which is coupled to the shaft through a lost motion device permitting a free relative rotation of 180. The gear wheel 27 meshes with a gear wheel 28 mounted on the shaft of an electric motor 29 which is preferably but not necessarily of the synchronous type. The shaft 23 also carries a gear wheel 30 which meshes with a gear wheel 31 of twice the size on a shaft 32. This shaft is carried in bearings 33 parallel with the shaft 23 and is provided with a cam 34 which operates on a two-way electric switch 35.

One form of electric circuit for this arrangement is shown in Figure 4. At the left-hand side of the diagram is the motor 29, the cam 34 driven thereby, and the switch 35. At the right-hand side is shown a second motor 37 driving a cam 33 which operates on a second two-way switch 39. This second motor 37, which is preferably a synchronous motor, operates as a timing device and may be disposed in any convenient position relative to the arrestment mechanism of Figures 1-3.

The operation of the arrangement is as follows: When the main switch 40 connecting the supply with the motor 37 is closed, this motor causes the cam 38 to rotate and the switch 39 is thus moved repeatedly from one posi- In addition the platform is provided with h tion to the other in predetermined time intervals. 7 With the switch 39 in the position shown, the motor 29 is deenergised, but when this switch is reversed the motor 29 will be energised and will remain so until its cam 34 reverses the switch The motor 29'will again be deenergised and will remain so until the switch 39 is again reversed. Since the

gearing

30, 31 between the motor 29 and its cam has a 2:1 ratio, once the motor 29 is energised the shaft 23 will travel through 360 before the motor stops again. The rotation of this shaft causes the balance to be arrested as described above and then to be actioned again, the balance remaining in this condition until the switch 39 is once more reversed and the motor 29 again energised. This cycle of operations will continue for so long as the switch is closed. Each time the beam is arrested it will be relocated and in consequence weighing may be carried out for long periods without any inconvenience apart from the temporary interruptions caused by arrestment. Even this may be advantageous since in the case of continuously recorded weighing the discontinuities in the chart caused by arrestment may serve as timing marks if the timing motor operates accurately as it will if it is a synchronous motor.

Other forms of timing device may of course be used. Thus the motor 37 could be replaced by a suitable clockwork. Figure 5 shows a further alternative which is suitable if accurate time intervals are not required. In this case the timer operates thermally. A bimetallic strip 43 is heated by a heater 44 which is energised by the supply through contacts 45. When the strip becomes hot enough it will bend to open the contacts 46 and close the contacts 47 of a two-way switch and at the same time will open the contacts of its heater circuit. After a certain time the strip will cool sufliciently to reclose the contacts 45 when the cycle will repeat.

The timing of the cycle of operations of the arrestment mechanism will of course be determined by requirements. Thus in one particular case it was arranged that the balance was arrested and at once actioned every six minutes. In another case, however, the balance was held actioned for five minutes and held arrested for the next ten minutes. In such a case the cam 34 would be mounted on the shaft 23 and given an appropriate contour. Other timing cycles may of course be obtained by means of appropriate adjustment of the contour of the earns 34 and 38 and the ratio of the

gearing

30, 31.

What we claim is:

l. A precision knife edge balance comprising arrestment mechanism effective when operated to relocate the knife edge on its bearing, a shaft having a cam thereon for operating the arrestment mechanism, an electric motor for rotating said shaft, a switch arranged to be actuated following a predetermined angular rotation of said shaft to de-energise said motor, and a timing device effective to energise said motor at predetermined time intervals.

2. A precision knife edge balance comprising arrestment mechanism effective when actuated to relocate the knife edge on its bearing, an electric motor arranged to rotate a cam shaft operating the arrestment mechanism, a first switch arranged to de-energise the motor following a predetermined angular movement of the shaft, and a synchronous motor controlling the periodic operation of a second switch effective to energise the first mentioned motor.

3. A precision knife edge balance as claimed in claim 2, in which the said first and second switches are two-way switches so connected that after the said first switch has been operated to de-energise the motor, subsequent operation of the second switch will be effective to re-energise the motor.

4. A precision knife edge balance comprising a beam supported on a hearing by a knife edge and arrestment mechanism effective when operated torelocate the beam and thus the knife edge on the bearing, a shaft mounted f r rotation in bearings and having a cam for operating the arrestment mechanism when the shaft is rotated, an electric motor for rotating the shaft, a lost motion device connecting the motor with the shaft, means for effecting manual rotation of the shaft within limits imposed by said lost motion device, an electric switch movable between two limit positions by means of a cam driven by said shaft and arranged to de-energise the motor following a predetermined angular movement of said shaft, and a timing device effective to energise said motor at predetermined intervals of time.

5. A precision knife edge balance as claimed in claim 4, in which said timing device is a synchronous motor arranged to actuate an electric switch by means of a cam.

6. An apparatus for effecting continuous weighing comprising a precision knife edge balance including an arrestment mechanism which is effective, when operated to the arrested position, to relocate the knife edges relatively to their bearing planes, power operated means for effecting momentary arrestment of the balance, and timing means comprising an electric motor operable for initiating the operation of such power means at predetermined time intervals during the weighing operation.

7. A precision knife edge balance comprising arrestment mechanism effective when operated to relocate the knife edge on its bearing, an electric motor for operating the arrestment mechanism, and a timing device for energizing the motor at predetermined time intervals, said timing device including a thermal switch.

8. In an apparatus for effecting cyclically interrupted continuou weighing, a precision knife edge balance including an mrestment mechanism for effecting arrestment of the balance comprising an arresting member operable to move and to guide the knife edge between an active station on its bearing plane and respectively an arrested station and including means operable for relocating in the arrested station the knife edge relative to its bearing plane, whereby said knife edge will accurately be positioned on its bearing plane when subsequently moved to the active station, power means for actuating said arrest- 6 ing member to move said edge to said arrested station, and timing means operable for cyclically initiating the operation of said power means at predetermined time intervals during the weighing operation.

9. In an apparatus for effecting cyclically interrupted continuous weighing, a precision knife edge balance including an arrestment mechanism for effecting arrestment of the balance comprising an arresting member operable to move and to guide the knife edge between an active station on its bearing plane and respectively an arrested station and including means for relocating in the arrested station the knife edge relative to its bearing plane, whereby said knife edge will accurately be positioned on its bearing plane when subsequently moved to the active station, power means for actuating said arresting membet to move said edge to said arrested station, and means operable for initiating the operation of said power means in accordance with a predetermined time cycle pattern during the weighing operation.

10. An apparatus for effecting continuous weighing comprising a precision knife edge balance including an arrestment mechanism which is effective, when operated to the arrested position, to relocate the knife edges relatively to their hearing planes, power operated means for effecting momentary arrestment of the balance, and timing means for initiating the operation of such power means at predetermined time intervals during the weighing operation, said timing means comprising a synchronous motor.

References Cited in the file of this patent UNITED STATES PATENTS 313,468 Becker Mar. 10, 1885 823,599 Hoepner June 17, 1906 1,132,880 Sartorius Mar. 23, 1915 2,233,868 Kish Mar. 4, 1941 2,260,691 Popov Oct. 28, 1941