THE APPLICATION FIELD

[0001] The present method and apparatus relate to the field of balancing rotating disks and in particular gemstone working members.

BACKGROUND

[0002] Rotating cylindrical or disk shaped bodies, although being symmetrical, need to be balanced; otherwise, they may cause undesired vibration. For example, vehicle wheels are balanced. Grinding wheels are balanced and many other examples of balancing can be found. Balancing of rotating masses is called dynamic balancing. Special instruments to measure the balance or unbalance and assist in the balancing process exist.

[0003] Grinding and polishing are the most common gemstone working (shaping) operations. The term "gemstone" includes diamonds, and other precious and semi¬ precious stones. Most commonly, gemstones are polished (worked) mechanically on a fast rotating heavy metal working member or scaife. Scaife, which has a diameter of around 350 mm and masss 15 - 20 kilograms rotates at speeds of 2500 - 5000 rpm. The quality of polished gemstones depends on the lack of vibration in the working member. In order to avoid vibration, each working member is balanced at manufacturing time. In addition to this, it is dynamically balanced when mounted in a gemstone working machine. [0004] The gemstone working industry has been practicing for a long time a working member balancing procedure that uses two sensors and expensive measurement instruments. An optical sensor is used to synchronize measurement of the rotation of the working member and to indicate the angle at which the maximal unbalance of the working member is measured by a second sensor. The balancing masses sometimes termed counterweights are placed at discrete and fixed angular locations and usually some residual imbalance is present.

[0005] Known prior art includes United States Patent No. 5,243,788 to Rossmann et al.

[0006] The diamond working industry would benefit by a method for dynamically balancing working members that would be simple, inexpensive and would result in acceptable working member balancing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The foregoing and other objects, features and advantages of the method and apparatus will be apparent from the more particular description of the exemplary embodiments of the method and apparatus, as illustrated in the accompanying drawings in which like reference numbers refer to the same parts throughout the different figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the method and apparatus.

[0008] Figure 1 is a schematic illustration of a gemstone working member with the balancing article;

[0009] Figure 2 is a schematic illustration of a partial assembly of the balancing article;

[00010] Figure 3 is a schematic illustration of the angular grid of the balancing article; [00011] Figure 4 is a schematic block diagram of an exemplary embodiment of the balancing apparatus;

[00012] Figure 5 is a schematic flow chart of the method of balancing a gemstone working member;

[00013] Figure 6 is a schematic illustration of some stages of iterative masses manipulation of the method of balancing a gemstone working member;

[00014] Figure 7 is a detailed schematic illustration of the counterweight positioning angle determination process;

[00015] Figure 8 is a schematic illustration of a moment vector diagram of the unbalanced forces;

[00016] Figure 9 is a schematic illustration of a prior art gemstone working machine;

[00017] Figure 10 is a schematic illustration of an exemplary embodiment of the gemstone working machine with a balancing apparatus;

[00018] Figure 11 is a schematic illustration of another exemplary embodiment of the gemstone working machine with a balancing apparatus;

DETAILED DESCRIPTION OF THE EXEMPLARY EMBOD YMENTS

[00019] By way of general introduction, before addressing the drawings in detail, it is noted here that certain exemplary and non-limiting implementations of the present disclosure provide a method of a rotating disk-like body and gemstone working member balancing. The disclosure also provides an apparatus enabling the method of a rotating disk-like body and gemstone working member balancing.

[00020] Reference is now made to Figure 1, which shows a balancing article 50 that may be permanently attached to a working member 20. Balancing article 50, a partial assembly of which is shown in Figure 2 includes a flange 54 having a circular groove 56. A pair of masses 60 that may be placed in groove 56 and resides in it permanently. Masses 60 have the freedom of movement along groove 56 and can slide in it. A cover 62 can lock masses 60 that project out of groove 56 in any desired angular position. Alternatively, locking screws 64 threaded in the body of masses 60 may lock masses 60. Generally, other locking means such as magnets, springs or similar devices may be used to lock masses 60 in a desired position. Masses 60 of balancing article 50 may be of equal mass. Gemstone working members are balanced during manufacture or maintenance. Nevertheless, fine-tuning of the working member balance may be achieved on a gemstone working machine.

[00021] Cover 62 bears an angular grid 66. Grid 66 (Figure 3) may have clockwise- directed gradations 70 and counterclockwise-directed gradations 72. In order to simplify the utilization of grid 66, gradations 70 and 72 may be color-coded. For example, clockwise-directed gradations 70 may be red and counterclockwise-directed gradations 72 may be blue. Any other color combination is possible, as well as different gradation shapes and form.

[00022] There are different types of balancing apparatuses that usually measure the balance (or unbalance) of a rotating body. Figure 4 is a schematic block diagram of a balance measuring apparatus. Balance measuring apparatus 90 includes a vibration sensor 92, such as a low cost dual axis accelerometer model ADXL202 or ADXL210 commercially available from Analog Devices, Inc., Norwood, MA, U.S.A., for detecting acceleration or vibration data which measures the magnitude and frequency of vibrations caused by an unbalanced rotating body. Processor 94 such as an 8-bit microcontroller or similar device processes the vibration data according to a predefined sequence. Command panel 96 assists the operator in sequencing the apparatus operation, and display 98 such as 7-segment two-line display, displays the results of processing and gives instructions to the operator.

[00023] Use of an accelerometer as a vibration sensor has some advantages over more traditional sensors. An accelerometer, unlike a microphone or a piezoelectric sensor, is a micro machined solid-state device, which incorporates certain signal processing electronics that makes it easier to use. Such devices are characterized by high linearity, low signal to noise ratio and high reliability.

[00024] Figure 5 is a schematic flow chart of the method of balancing a gemstone working member. Although the following detailed disclosure of the method and of the apparatus by way of example uses a gemstone working member, it is clear that it is applicable to any disk-like rotating body. Initially a gemstone working member 20 (Figure 1), a balancing article 50 (Figure 1) and a balance measuring apparatus 90 (Figure 4) may be provided. Article 50 may be built as a permanent part of a working member or may fit existing working members. For balancing purposes, balancing article 50 may be attached to working member 20. In order to determine the existing unbalance of working member 20 (block 110) vibration sensor (accelerometer) 92 of balance measuring apparatus 90 may be attached to a bearing housing that supports the axis on which the working member rotates and the maximal vibration magnitude value Mo of the existing or natural unbalance is measured. It is necessary to mention that sensor 92 may be attached to any other point enabling reliable unbalance reading.

[00025] Placement of a known mass at an arbitrary angular location on the grid, may introduce a predetermined unbalance of working member 20. The location where the mass was placed may be adopted as a reference angular point (block 114). A pair of masses 60 placed in groove 56 of balancing article 50 and having a freedom of movement along the groove may introduce unbalances of different magnitude. Masses 60 may be of equal mass and manipulation of masses 60 may form a mass equivalent to the difference of the masses, to the mass of one of the masses, and to the sum of the masses.

[00026] Next, an unbalance caused by an equivalent of one mass (unit mass) may be introduced. Positioning masses 60 at an angle of 120 degrees with respect to each other may form a mass equivalent to the mass of one of the masses. Actually it is the sum of the projection of the two equal masses, since cos (60°) = 0.5. The bisector of the angle or one of the positions of masses 60 may be selected as a reference point or line in relation to which the angles are determined. Figure 6B, illustrates this stage of iterative mass manipulation. For simplicity of explanation, balancing article 50 is shown with cover 62 removed. Cover 62 may bear angular grid 66 that assists in positioning masses 60 at a desired angular position. Locking screws 64 of masses 60 lock masses 60 in position. Apparatus 90 may measure the magnitude Mi of the introduced unbalance (block 114).

[00027] It is necessary to mention that determination of working member existing unbalance Mo (block 110) may be performed with or without masses added to working member 20. As shown in Figure 6A by positioning masses 60 on the same line opposing each other or at an angular distance of 180 degrees they may be manipulated to form a mass equivalent to the difference of the masses. Since masses 60 may have equal mass, they are mutually canceling each other and do not affect the existing balance.

[00028] Generally, as will be shown below, knowledge of the existing unbalance magnitude and the magnitude of the unbalance introduced by a mass equivalent to the mass of one of the masses may be sufficient for finding the balancing mass angular positions or simply the counterweights. However, the need to know the angle at which the counterweight has to be positioned and the accuracy of the counterweight determination require introduction and measurement of at least one additional unbalance. Repositioning of masses 60 to a configuration shown in Figure 6C, may introduce an unbalance with a mass equivalent to the mass of the sum of the masses (two unit masses). Apparatus 90 measures the magnitude M2 of the intentionally introduced unbalance (block 118).

[00029] Apparatus 90 may further process the value of the magnitudes of the existing and introduced unbalance to determine the value and angular position of the existing unbalance compensation counterweights. Practically, since the masses are equal and on a known radius, it is the angle at which the pair of masses may be positioned to form an equivalent mass that compensates the existing unbalance. Processing includes filtering vibration data to separate it from noise and other components provided by the two-axis accelerometer, converting it from analog to digital data and making a histogram for statistically determining the most probable vibration magnitude value for each of the unbalances. The histogram may include measurements of at least 200 rotations of the working member or even measurements of at least 500 rotations of the working member.

[00030] The values of the counterweights or balancing masses (block 122) are found (Figure 7) by squaring each unbalance value (unbalance magnitude) caused by vibration Mo, Mi and M2, summing the squares of the existing unbalance magnitude Mo and the unbalance magnitude M2 introduced by the mass equivalent to the sum of the masses (two unit masses). The multiplied by two square of the unbalance magnitude Mi introduced by the mass equivalent to the unit of the masses is subtracted from the sum of the squares and the result is divided by two. The angle at which the counterweight/s has to be positioned is found by summing the squares of the existing unbalance magnitude Mo and of the unbalance magnitude A that may be generated by a counterweight or balancing mass. The square of the unbalance magnitude Mi introduced by the mass equivalent to the unit of the masses is subtracted from this sum, and the result of the subtraction is divided by the multiplied by two values of the counterweight introduced magnitude A multiplied by the value of the existing unbalance magnitude Mo.

[00031] Apparatus 90 may be further characterized in that based on the results of processing; apparatus 90 may directly display the unbalance compensation counterweight (balancing mass) and the angle (block 122) with respect to the reference point at which the counterweight has to be positioned. Actually, since the balancing masses are equal, it is enough to know the angle at which they have to be positioned. According to these readings and with the help of grid 66 masses 60 may be repositioned and locked (block 124) balancing the working member. The same masses 60 placed in groove 56 may be used to introduce a desired counter balance and may be used as unbalance compensation masses or counterweights. There is no need for finding the radius at which the masses should be positioned since the masses are in a groove having fixed and known radius.

[00032] The described operations do not necessary lead to a balanced working member (block 126). If the working member is not balanced, all that is needed is to mirror the angles and reposition masses 60 (block 128). The working member in this case becomes balanced. The repositioning of masses 60 may be easy to make using the opposite grid 66 gradations. For example if the initial reference and positioning of the masses was done according to the clockwise running grid gradations, the mirroring may be done using the counter clockwise running gradation and vise versa.

[00033] The need to mirror the angle and the absence of balance (block 126) are because similar results (countermass and angle) may be obtained from the opposite directed vectors M2 and Mo'. Figure 8 A is a schematic illustration of the moment vector diagram of the unbalanced forces. The unbalance magnitude^ that the countermass has to introduce may be found using the well known cosine relation Mj2 = A2 + Mo2 - 2AMo cos(θ). This equation contains however, two unknown variables. A second equation includes the desired unbalance introduced by the mass equivalent to the sum of the masses and is based on the same variables M22 = (2A)2 + M02 - 2(2A)M0 cos(θ). Resolving both of the equations, it is possible to provide a solution enabling determination of balancing countermasss and/or their positioning angle. It is clear however, that as shown in Figure 8B, similar results could be obtained from the opposite directed vectors M2' and Mo'.

[00034] Generally, balance measuring instruments are expensive and one instrument is used for balancing tens of gemstone working machines. This causes an increase in machine idle time and in the cost of working gemstones. The low cost of the balance measuring apparatus disclosed allows mounting it in each gemstone working machine. Commercially available gemstone working machines usually include a table like frame 150 (Figure 9) supporting the assembly of working member 20 and motor 146. Controller 144 controls operation of such a machine. Controller 144 may include a processor (not shown), display 154 and command panel 156 among other devices.

[00035] One exemplary embodiment of gemstone working machine 160, illustrated in Figure 10, in addition to the earlier described parts, may include balancing article 50, vibration sensor 92, processor 94 (not shown), command panel 96 and display 98. Vibration sensor 92 may be permanently attached to a bearing cover of the motor housing or any other part that supports reliable vibration magnitude sensing. Packaged in housing processor 94, command panel 96 and display 98 may be located in a convenient place for operator access. The operation of the balancing instrument and the balancing method are similar to the earlier described method.

[00036] In an alternative exemplary embodiment of gemstone working machine 160, illustrated in Figure 11, processor 94, (not shown) command panel 96 and display 98 may be combined with analogous units of controller 144 providing further cost savings and simplifying machine balancing and operation. [00037] The built-in balancing apparatus simplifies working member balancing and increases the machine availability. This further reduces the cost of working gemstones.

[00038] The present method enables a fast and easy dynamic balancing of a disk-like rotating body and in particular a gemstone working member. The balancing is performed according to a predefined sequence and does not require skilled employee participation.

[00039] Balancing is performed by counterweights that are permanently attached to the gemstone working member. The counterweights slide in a groove and may be positioned at any desired angle providing accurate balancing of the working member. A grid assists in correct positioning of the counterweights.

[00040] It will be further appreciated by persons skilled in the art that the scope of the present method and apparatus are not limited to what has been shown and described hereinabove by way of example. Rather, the scope of the method and apparatus is limited solely by the claims, which follow.