Abstract:
A machine for balancing a rotating member includes hard bearing balancing apparatus for determining the magnitude and circumaxial location of imbalance. A sensor responds to the position of the rotating member. A computer receives signals from the balancing apparatus and the sensor and determines the location of one or more projectiles to be fired at the member. A firing mechanism including a piezoelectric actuator fires the projectiles in timed relationship with the rotation of the member so as to position the projectiles as required for balancing.

Description:
BACKGROUND OF THE INVENTION 
   Attempts to balance members during rotation have not been commercially successful in the past. Accordingly, it is the general object of the present invention to provide a machine for balancing a member during rotation in a procedure much more expeditious and at least as accurate as manual balancing and which is highly efficient and reliable over a long service life. 
   RELATED APPLICATIONS 
   The filing date of Provisional Application entitled Method and Apparatus for Balancing Fan and Blower Assemblies filed Jan. 9, 2004 is hereby claimed for the present application and the Provision Application is hereby incorporated herein by reference. 
   U.S. Patent Application entitled A Rotatable Member with an Annular Groove for Dynamic Balancing During Rotation filed Jan. 9, 2004 is hereby incorporated herein by reference. 
   SUMMARY OF THE INVENTION 
   In fulfillment of the aforementioned object and in accordance with the present invention, a machine for balancing a rotating member comprises apparatus for determining the magnitude and the circumaxial location of the imbalance of the member. A sensor responsive to the position of reference mark on the rotating member is also provided together with at least one balancing projectile of known weight. A computer is connected with and receives signals from the first mentioned apparatus and the sensor and determines the location of one or more projectiles to be fired at the member in timed relationship with rotation of the member whereby to balance the same within a specified tolerance. A fast acting firing mechanism comprises an electrical-mechanical transducer assembly with a reaction time compatible with the speed of rotation of the rotating member is operated by the computer to fire a projectile at the member at the circumaxial location determined by the computer. The balancing machine of the invention is compatible with rotational speeds of a member to be balanced in both lower speed ranges below 1000 R.P.M. as well as higher speeds at least up to 5000 R.P.M. 
   Operation at high speed and with a high degree of accuracy, as much as five times that achieved manually, is attributable at least in part to the use of a piezoelectric stack as a transducer-actuator for receiving an electrical signal from the computer and rapidly converting to a mechanical signal for triggering a momentary valve which releases an explosive burst of air for propelling a projectile toward the rotating member. While it is anticipated that future piezoelectric stack actuators with enhanced output characteristics will accommodate system designs wherein the actuator directly triggers a momentary valve, or perhaps employs a motion amplifier along, the presently preferred design includes a motion amplifier in the form of a lever and a force amplifier in the form of a stored energy device operated by the lever. A loading mechanism operable in timed relationship with the firing mechanism includes a shuttle movable from a loading position to a firing position and which has a chamber for receiving and transporting projectiles and for positioning projectiles to be propelled by the explosive burst of air mentioned above. In the firing position of the shuttle, a through opening communicating with the chamber is open at one end to the momentary valve for receipt of the burst of air and that other end for the discharge of projectiles toward the rotating member. A magnet in the shuttle forms a means for retaining projectiles in position in the chamber during transfer and prior to discharge. 
   A vibratory feeder and supply tube deliver projectiles to the loading mechanism at the loading position. 
   Finally, the method of the invention comprises the steps of determining the location of imbalance of a rotating member, calculating the amount and position of balancing weight required to balance the member, calculating the time to fire based on speed of rotation and total firing time, and firing one or more projectiles as required at the member to balance the same. 
   When the weight required to balance a rotating member is not an integral number of projectiles, the method requires a further determination of two or more locations which are spaced circumaxially from the point of imbalance but which will balance the member. Projectiles are then fired at these locations. 
   The aforementioned condition may occur when less than a single projectile is required at the point of imbalance or when a first integral projectile is required at the point of imbalance with additional projectiles required at spaced circumaxial positions for an additional non-integral correction. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  of the drawings is a schematic view of the balancing machine of the present invention, 
       FIG. 2  is a schematic view of the loading mechanism of the invention, and 
       FIG. 3  is a schematic view of the loading mechanism of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring initially to  FIG. 1 , it will be observed that a member to be balanced takes the form of a centrifugal air impeller indicated generally at  10 . The impeller  10  is mounted on a conventional apparatus known as a hard bearing balancing machine. Various machines may be employed with a SCHENCK machine presently preferred. The impeller shown is rotated at a constant speed of approximately 1700 R.P.M. but the balancing machine of the invention can accommodate rotational speeds from the low hundred to at least 5000 R.P.M. The balancing machine  12  responds to unbalanced forces and reports to a computer  14  via broken line  16  advising as to the magnitude and circumaxial location of imbalance of the impeller  10 . Sensor  18 , preferably a diffuse laser sensor, responds to instantaneous position of the impeller which is provided with a reference mark legible to the sensor and advises the computer accordingly. 
   The computer  14  employing the information from the balancing apparatus and the sensor, and considering the known weight of the balance projectiles, calculates the required number of projectiles and their respective circumaxial locations to balance the rotating member. The computer thus determines the precise instant in time to send a signal  22  to piezoelectric stack transducer-actuator  20  to discharge a projectile so that it will engage the rotating member at the desired location. All time lags resulting from operation of the piezoelectric stack and other elements to be described below are considered by the computer with precise positioning of the projectile resulting. An appropriately programmed computer should be of a high-speed type but may be conventional. 
   The piezoelectric transducer-actuator stack  20  has an exceptionally high reaction time. 
   Mechanical output element  24  of the actuator  20  is operatively associated with the right hand end of lever  26  in  FIG. 1  which has a pivot point  28  providing for amplification of the output movement of the element  24 . At its left hand end, the lever  26  has a small detent  30  engaging a pin  32  on a spring-loaded striker  34  shown in  FIG. 1  in an armed or cocked position. The striker  34  serves as a force amplification means and carries a small pin  36  which engages a trigger pin  38  on a momentary valve  40  when the detent  30  is pivoted downwardly slightly releasing the pin  32  and permitting the striker to rotate in a counter-clockwise direction. The striker  34  is returned to its armed position by a small pneumatic rotary actuator, not shown, but which is connected to and operated by the computer  14  by broken line  39 . 
   Momentary valve  40  which may be conventional serves to release an explosive burst of air to a firing chamber  41  in a loading mechanism  44  best illustrated in  FIGS. 2 and 3 . Supply conduit  42  extending from the valve communicates with a source of air under pressure. 
   Referring now more particularly to the loading mechanism  44  in the left and right hand views in  FIGS. 2 and 3 , a shuttle  46  moves between loading and firing positions illustrated respectively in the left and right hand views in  FIGS. 2 and 3 . In  FIG. 2 , with the shuttle in the loading position, a projectile is shown in the shuttle chamber  41  having been delivered by a tube  50 ,  FIG. 1 , which extends from a vibratory feeder  52 . A magnet  54  holds the projectile in position in the chamber, it being noted that a right portion of the chamber is somewhat smaller than a left hand portion thereof with the projectile approximately fitting the said left hand portion. It should also be noted that the chamber has a through opening which communicates with the supply tube  50  at the left in  FIG. 2  and with a projectile discharge barrel  56  in  FIG. 3 . Further in  FIG. 3 , the chamber  41  communicates at the right with the valve  40 , not shown, for receipt of the burst of air as aforesaid. 
   Air cylinder  58  transfers the shuttle  46  between loading and firing positions under the control of the computer  14  via broken line  60 . As mentioned, projectiles are delivered to the chamber  41  and are held in position by magnet  54 . The projectiles are preferably metallic and at the present time small bearings or BB&#39;s of the type used in a powered BB gun may be used. The weight of the projectiles is of course determined and entered in the computer memory. 
   As the shuttle is moved downwardly to its firing position the chamber  41  is sealed by small annular seals  62  and  64  respectively above and below the chamber which cooperate with a slightly tapered housing opening in which the shuttle slides. Thus, at the firing position of  FIG. 3 , the chamber  41  is conditioned to receive the air burst  43  from the valve  40  whereupon the projectile therein is propelled toward the impeller  10 ,  FIG. 1 . Exit sensor  61  reports successful firings to the computer  14  via broken line  59  and may be employed to determine the response time of the firing mechanism. 
   On reaching the impeller  10 , the projectile is captured and retained in position by an annular groove  66  best shown in  FIG. 1  and more fully described and illustrated in the above-mentioned U.S. Application. 
   From the foregoing it will be apparent that the balancing machine of the present invention as a whole has an exceptionally fast reaction time, due in large part to the incorporation of the piezoelectric actuator, as well as extremely high accuracy characteristics, this due at least in part to the incorporation of a high speed computer. The total time in balancing a rotating member with the machine of the present invention may be as little as one tenth that required in a manual balancing procedure. It is also to be noted, as mentioned above, that the accuracy balancing achieved with the machine may be as high as five times that realized in manual balancing.