GB2097101A - Unbalance compensator and method of distributing balancing mass in same - Google Patents

Abstract

A dynamic balancing system for rotary elements, e.g. grinding wheels, comprises a fluid balancing mass (16) partially filling three or more chambers (5, 6, 7, 8) the vapor of the fluid being free to communicate between chambers. A change in mass distribution is achieved by heating the fluid in a chamber and conducting the vapor so produced to another chamber where the vapor condenses. A warmer chamber thereby loses mass to a cooler chamber. Electronic vibration measuring means are generally employed to determine which chambers and what degree of heating are required to improve the state of balance. <IMAGE>

Description

SPECIFICATION Unbalancing compensator and method of distributing balancing mass in same This invention relates to a balancing system for making repetitive balance corrections on rotary ele mentsofmachines (grinders, high-speed lathes and centrifuges, as examples) that undergo variations of balance during normal operation. Imbalance is corrected by remote control while such elements are rotating.

Certain types of rotating machines which need balancing changes generally require stopping when an unacceptable level of vibration is reached and manually shifting weights to positions indicated by a vibration instrument in order to obtain the desired balance. Several cycles of trial spin-ups, measurement, stopping and readjustment are necessary because the effect of an adjustment cannot be observed while the adjustment is in progress, but only after the adjustment is made as determined by the subsequent spin-up and measurement.

There is a distinct advantage both in reducing procedure time and in greater accuracy of balance by performing the weight adjustment while simultaneously monitoring the effects of such adjustment, i.e.

automatically without stopping the machine. Balancers which operate while the spindle is revolving, commonly known as unbalance compensators, can be broadly classified into two categories, (1) mechanical and (2) fluid.

Nearly all mechanical types share one problem in common which is the inability to make both large and fine balance corrections. Large weights necessary for coarse corrections must be minutely adjusted to make fine corrections. Sensitive adjustment of large weights is even more difficult at high speed due to high centrifugal stresses. Fine balance corrections are easier using small weights, but this limits the correction capacity of the compensator.

Mechanical compensators typically cannot be used on applications where a large through-hole in the device is required.

One type of mechanical balancer uses mobile weights such as two or more ball bearings free to roll to any point in a race. Most machine spindles are mounted "hard," that is the resonant frequency of the spindle is above the normal operating speed, in which case this type of balancer would actually worsen the state of balance.

In the category of fluid type compensators, two main classes are found, (1 ) annular chamber types, and (2) multiple chamber types.

Devices of the first type, after Lebanc U.S. patent no. 1,209,730, have an annular tube or channel par tiallyfilled with fluid free to communicate everywhere along the annulus. Prerequisite to the function of this balancer is "soft" suspension of the spindle. Balance correction cannot be maintained independent of vibration levels. Such a device can never in principle eliminate vibration but only reduce it through the effect of "mass damping".

The other class of fluid balancer incorporate multiple circumferentially disposed chambers which communicate not with one another, but with annular grooves, one groove per chamber. Stationary nozzles direct jets of fluid into adjacent grooves to fill respective chambers. Upon entering a chamber the fluid cannot be removed except by stopping the spindle and allowing the fluid to fall out by gravity.

This is an open-cycle and irreversible process.

According to the present invention there is provided a spindle mounted balancer having a plurality of circumferentially disposed chambers partially filled with fluid having liquid and vapor phases and serving as a distributable balancing mass, said chambers being connected by suitable means to allow free flow of vapor of the fluid between chambers, and means for creating a differential condition between chambers such that vapor of said fluid passes therebetween.

The balancer is of closed-loop, multiple chamber design. Balancing mass may be indefinitely transferred among chambers without loss of balance at stand-still.

Fluid balancing mass is not moved as a body, but incrementally transferred as a vapor, making possible precise balance corrections while retaining high correction capacity. Absence of moving weights and associated mechanisms permit operation to speeds limited only by structural strength considerations.

Balancing mass is transferred between symmetrically and circumferentially disposed chambers.

Mass transfer may conveniently be accomplished by creating a temperature difference between fluids contained in opposing chambers. Higher vapor pressure of warmer fluid impels flow of vapor through a transfer tube to an opposing cooler chamber or chambers wherein it condenses.

Port ends of the transfer tubes are located in the chambers in such a manner as to prevent fluid from entering the tube and passing to another chamber whether the compensator is rotating or at stand-still in any position. Fluid is thus trapped while only vapor is free to move between chambers.

Producing a temperature difference between fluid in opposing chambers may be either by heating or cooling means acting alone or in combination. While not so limited, the heating or cooling means may be electrical in nature such as resistance heating or Peltier Effect cooling. Provision is made on the chambers for dissipation or absorption of heat to or from the balancing fluid and vapor by means such as fins or convolutions exposed to ambient conditions. If electrical heating or cooling means are utilized electric current may be conducted through slip-rings to the rotating compensator from an outside power supply or may originate from a battery within the compensator.

Chamber selection may be by external means such as switches or relays or by signal responsive means internal to the compensator. Such control signals may be electromagnetic, acoustic or other non-mechanical means to obviate direct physical contact of non-rotating elements with the compensator.

Conventional electronic vibration measuring means determine the amount and location of unbalance so that proper chambers may be selected for mass transfer.

A further aspect of the invention provides a method of distributing balancing mass in a spindle-mounted balancer comprising steps of: adding and/or removing heat to cause a temperature difference to exist between fluid contained in generally circumferentially disposed chambers; and permitting fluid vapor pressure difference developed by said temperature difference to cause flow of vapor of said fluid between said chambers.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates schematically a balance compensator embodying the invention applied to a grinding machine; Figure 2 shows diagrammatically a four chamber compensator embodying the invention; Figure 3 is a tranverse sectional view of the compensator of Figure 2; Figure 4 is an axial sectional view of the compensator of Figure 3; Figures 5 and 6 are detail views of corrugated metal hose as used to form the chambers of the compensator; and Figure7 isaviewsimilarto Figure2 butshowing a three chamber compensator; Figure 1 shows schematically a typical application of the invention on a grinding machine. Compensator 1 is mounted adjacent to grinding wheel 22.

Vibration transducer 4 and proximity sensor 5 provide vibration magnitude and spindle positional signals respectively to electronic instrument 3.

Instrument 3 indicates the location and amount of unbalance in wheel 22. This can be done by monitoring the phase angle of vibration signal 4 in relation to the reference signal 3, the phase angle indicating the circumferential location of imbalance. The proper compensator chamber is selected and controlled through slip-rings 21. In some applications the compensator may be controlled automatically by instrument3 as shown in Figure 1.

Schematic diagrams of four chamber and three chamber compensator configurations are shown in Figure 2 and Figure 7 respectively. Partitions 23 define end boundaries of the chambers. Heating elements 9 permit heating individual chambers independently of other chambers.

In Figure 2 opposite chambers 6 and 8 communicate vapor therebetween via transfer tube 10. Similarly, chambers 5 and 7 communicate through tube 11. Figure 7 shows an alternate embodiment where all chambers are in murual communication through transfer tubes 24.

Figure 3 and Figure 4 show transverse and axial sections respectively of the type of configuration represented in Figure 2. Referring to Figure 4, opposing chambers 6 and 8 consist of corrugated metal hose, shown in greater detail in Figures 5 and 6.

Chamber convolutions 15 provide increased heat transfer surface area in contact with balancing fluid 16 internally and with the surrounding medium, usually air, externally. Heating element wire 9, sheathed with electrical insulation, wraps spirally around the chambers between the convolutions.

Element leads are bundled in cable 19 which terminates at brushes contacting slip-rings 18. The sliprings ride in bearings 20 supported by slip-ring housing 21 mounted on face of compensator housing 1.

The brushes rotate with the compensator while the rings remain stationary. Leads from the stationary slip-rings are contained in cable 17 connected to a power supply and control means not shown. Holes 13 and 14, having a difference in radial spacing, serve to pump the surrounding medium such as air around the chambers for heat dissipation purposes.

Figures 3 and 4 clearly show how transfer tubes 10 and 11 terminate with open ends located near the three-dimensional geometric centers of the chambers. Fluid 16 only partially fills the chamber system such that under no conditions is it possible for any chamberto containfluidfilling more than half the total volume thereof. Thus the surface level of fluid 16 never reaches the open ends of transfer tubes 10 and 11 whether the compensator is rotating or at stand-still. The chamber volume not occupied by fluid also functions as a vapor condenser with heat dissipation surface area provided by convolutions 15.

It should be understood that the above description of operation and construction of the unbalance compensator discloses one specific embodiment utilizing the principle of vaporization and condensation of the balancing mass. Any means such as heating, cooling, ultrasonics, chemical or other means for achieving vaporization and condensation of a balancing massforthe purpose of transferring or redistributing spatially such mass in a balancing device lie within the purview and scope of this invention.

Claims (11)

1. Aspindle-mounted balancer having a plurality of circumferentially disposed chambers partially filled with fluid having liquid and vapor phases and serving as a distributable balancing mass, said chambers being connected by suitable means to allow free flow of vapor of the fluid between chambers, and means for creating a differential condition between chambers such that vapor of said fluid passes therebetween.

2. A spindle-mounted balancer as claimed in claim 1, wherein the means to create a differential condition comprises means to cause and permit heat flow into and out of said fluid and said vapor contained in the chambers.

3. A spindle-mounted balancer as claimed in claim 2, wherein said chambers are fabricated with fins to facilitate transfer of heat to said balancing fluid and said vapor and from them to the surrounding medium.

4. Aspindle-mounted balancer as claimed in claim 1,2 or 3, wherein said chambers are fabricated of convoluted tubing, the convolutions providing a large surface area both to said fluid and said vapor inside said chambers and to the ambient medium external to said chambers.

5. A spindle-mounted balancer as claimed in any preceding claim, wherein electric heating element wire, suitably electrically insulated, is wrapped spirally around said chambers for the purpose of heating said fluid contained therein.

6. A spindle-mounted balancer as claimed in claim 1, including transfer tubes or channels connecting the chambers for the purposes of communicating the vapor therebetween.

7. A method of distributing balancing mass in a spindle-mounted balancer comprising steps of: adding and/or removing heat to cause a temperature difference to exist between fluid contained in generally circumferentially disposed chambers; and permitting fluid vapor pressure difference developed by said temperature difference to cause flow of vapor of said fluid between said chambers.

8. A method according to claim 7 wherein balancing liquid contained in a first said chamber is heated in order to produce vapor therefrom; said vapor is transferred to one or more other said chambers; and said vapor is caused to condense in said one or more other said chambers by a cooling process.

9. A method according to claim 7 or 8, wherein said liquid is trapped in said chambers under conditions of rotation or stand-still in any position by locating portends of vapor communicating means substantially at three-dimensional geometric centres of said chambers; and filling said chambers on the average with a volume of said liquid one fourth, or less as determined by the number of chambers and the manner of intercommunication thereof, of the total cavity volume of said chambers.

10. A method as claimed in claim 9, wherein the total volume of liquid in the chambers and connecting passages is not more than half the volume of the chambers and connecting passages.

11. A method of distributing balancing mass in a balance substantially as herein described with reference to and as illustrated in the accompanying drawings.