Patent GB-732438-A (GB)
Title: Apparatus for balancing a rotatable body
IPC: G01M1/30
Filed: 1951-11-16
Abstract: 732,438. Balancing and testing balance of rotary bodies. SJOSTRAND, H. E. Nov. 16, 1951 [Nov. 16, 1950; July 26, 1951], No. 26964/51. Class 106 (2). [Also in Group XXXV] An apparatus testing want of balance and for balancing a rotatable body comprises bearings for the body, means for rotating the body, a tool operable intermittently on the body, means controlled by the vibrations of the body for adjusting the phase angle of the operating cycles of said tool with respect to the rotary motion of the body to successively reduce the unbalance of the body, and means causing the intermittent operation of the tool to be positively controlled by a rotatable member rotating in dependence on the rotation of the body to be balanced. As shown in Fig. 1, a body 20 to be balanced is mounted on a shaft 21 held in bearings 22 and 23. The bearing 22 is fixed relatively to a main base 24 but the bearing 23 is capable of vibrating in a direction at right angles to the shaft 21 in a plane parallel to the base 24. The bearing 23, Fig. 3, may comprise a roller bearing 56 slidable between opposed strips 55, 57 against the action of opposed resilient means such as the rubber members 58, 59. When the unbalanced body 20 is rotated by asynchronous motor 26 the resulting horizontal oscillations of the roller bearing 56 are transmitted by a rod 63 to a leaf-spring 64 having an electrical contact at its upper end. The leaf-spring 64 is secured at its lower end to an oil container 67 wherein is . pivoted at 66 a switch member 65 having a contact 71 biased towards the contact 72 by a spring 70. The switch member 65 also carries at its upper end a switch contact 74 for engagement with an adjustable electrical contact 73. The lower end 68 of the switch member 65 is paddle-shaped and is immersed in the oil 69 in the container for damping purposes. Thus, if the body 20 and hence the rod 63 are vibrating rapidly the spring 64 will repeatedly contact the switch member 65 and hold the contact 74 away from the contact 73 until the body 20 has been balanced and all vibrations cease. The cutting tool 45, Fig. 1, having a single radially directed cutting edge, is mounted on a pair of travelling carriages 39 and 40 and is rotated by a synchronous motor 43 having a speed equal to that of the motor 26. The shaft of the motor 43 carries two slip-rings and a commutator comprising two segments 52, 53 separated by insulation 51 of sufficient width to prevent the segments 52, 53 from being short-circuited by a single brush 54 bearing against the commutator. The apparatus includes an electric motor 31 capable of turning the stator of the synchronous motor 26 about its axis. Method of operation. The two synchronous motors 26 and 43 are set in motion to rotate at equal speeds and the vibrations set up in the bearing 23 by the unbalanced mass of the body 20 causes the contacts 71 and 72 to momentarily close each time the body 20 reaches its maximum horizontal deflection (to the right in Fig. 3). A circuit is then closed through the switch member 65, the contacts 71, 72, the spring 64, the brush 54, the segment 52, the slip-ring 46, the brush 48 and through a coil of a relay which closes the circuit of the motor 31. The motor 31 then rotates in such a direction as to turn the stator of the driving motor 2.6 clockwise as viewed in Fig. 2. The motor 31 will continue to rotate until one of the insulating laminae 51 occupies a position under the brush 54, the circuit to the motor 31 then being interrupted. The arrangement is such that the driving motor 26 and the cutter motor 43 are now in correct phase relationship for a cutting operation whilst still rotating in synchronism. The rotating cutting tool 45 is now fed by a hand wheel 41 into engagement with the body 20, radially towards the axis of the rotor so that for every revolution of the body 20, material is removed from a definite sector of the heaviest side thereof. The unbalance is thereby gradually reduced until it has wholly or mostly disappeared when the contact 74 will engage the contact 73 energizing a relay causing a lever to trip in a manner allowing the cutting too] 45 to be withdrawn from the body 20 by a spring. Alternative modifications. The motor 31 may rotate the stator of the cutter motor 43 instead of the driving motor 26. Alternatively the motor 31 may be replaced by a hand wheel used in conjunction with an indicating lamp or the like for indicating the correct phase relationship between the driving motor 26 and the cutter. motor 43. Instead of a single cutting edge on the cutting tool 45, two or more cutting edges may be arranged together. The cutting tool may be actuated by an eccentric mounted on the extension 44 of the synchronous motor 43 through a link, the tool being axially guided in an extension of the motor body or casing. Instead of the separate synchronous motors 26 and 43, a single common driving motor may be used with a mechanical phasechanging device in the transmission mechanism between the driving motor and the body 20 or the cutting-tool. Balancing atboth ends of the body 20. The balancing arrangement can be modified for simultaneously balancing both ends of therotatable body. For this the bearing 22 is replaced by a bearing similar to the bearing 23 and is associated with a second cutting motor 43 on the usual guides. In this case the motors 43 must have their stators journalled upon their carriages to permit independent adjustment of their phase relationship with the motor 26 in accordance with the oscillations of each end of the shaft 21. Adding material to the. unbalanced body. The unbalance of the body 20 may be removed by applying material to the lightest side thereof. Thus, as shown in Fig. 7, a nozzle 110 may be provided for continually spraying paint, molten metal or the like towards a deflector wheel 107 between it and the end surface of the body 20. At one point on its circumference the deflector wheel 107 has an opening 111 which moves past the nozzle 110 once for every revolution of the motor 43, permitting the spray to pass therethrough and impinge on the end of the body 20. The direction of the spray is preferably parallel to the axis of the body 20. Indicating device. In conjunction with the above, a device may be used to indicate the instantaneous phase relationships and magnitudes of the unbalance at each end of the body. For this purpose an apparatus as shown in Fig. 9 may be used at each end. As before, the shaft 21 is caused to oscillate a rod 136 acting against a contact arm 124, the arm 124 being biased against the rod 136 by a spring 127 and having a spade-shaped end 129 immersed in oil 130. The arm 124 acts against a pointer 156 whose deflection can be read on a scale 160 and the whole is such that, due to the action of the oil 130 on the spade-shaped end 129, the pointer 155 indicates the maximum deflection of the rod 136, at any instant, per revolution of the shaft'21 and thus the out-of-balance of the body at that end. A glow discharge lamp 148 is mounted on shaft 144 rotating in synchronism with the body to be balanced. Through contacts 131 and 135, that close momentarily during every revolution of the body 21 whilst it is unbalanced, the lamp 148 is caused to flash. By means of a scale 150, and knowing the phase relationship between the lamp 148 and the body 21, the position of the out-of-balance load on the body can be determined.