Abstract:
The load applied to a scoring wheel to the combined load of a first predetermined constant load and a second variable load. The second load is varied in response to changes in the scoring speed to provide a uniform scoring depth.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to cutting glass sheets and in particular to a cutting head assembly that responds quickly to changes in the load applied to a cutting wheel of a cutting assembly to control the quality of the cut glass edge. 
     2. 2A Technical Considerations 
     The quality of a cut glass edge obtained in a cutting operation using conventional scoring and breaking techniques depends in part upon the quality of the scored line. It is preferred to have a constant scoring depth which provides a uniform edge quality after removing trim from the glass sheet. When scoring a curvilinear line, and in particular when scoring sharp corners of a glass sheet, for example an automotive window, the speed at which the scoring wheel travels along the glass sheet is reduced so that the wheel can better follow the desired contour to be scored. As scoring speed decreases, the load applied to the cutting wheel must be increased to maintain the desired scoring depth. The pressure on the cutting wheel can be provided by a pneumatic cylinder and controlled by varying the load from the cylinder. However, these types of cylinders have a slow response time and cannot increase and decrease the load applied to the cutting wheel at a fast enough rate to optimize cutting speed. As a result, when scoring the glass at optimal speed, portions of the scored perimeter will not be scored at the optimal load required to provide constant scoring depth. 
     It would be advantageous if variations in the loading required to maintain the proper scoring depth could be controlled to precisely provide the necessary loading required for a given scoring speed and further to be able to quickly change the load in response to changes in scoring speed so as to maintain optimal scoring depth and consistent edge quality while providing maximum scoring speed. 
     2B. Patents of Interest 
     U.S. Pat. No. 3,742,793 to Gray et al. teaches a cutter assembly and a double acting pneumatic cylinder and piston. The cutter assembly is connected to the piston which is operable to urge the cutter assembly towards the surface to be scored. 
     U.S. Pat. Nos. 3,756,104 to Bier et al. and 3,760,997 to Bier teach the cutting of glass using a cutter head connected to a constant reluctance motor. Pressure exerted by the cutter head responds to changes in the current supplied to the motor making it possible to vary the depth of the score as desired during the making of the pattern cut. 
     U.S. Pat. No. 3,880,028 to Frederick Jr. teaches a method and apparatus for monitoring and controlling glass cutting. Sound waves produced by scoring the glass in a cutting operation are detected and correlated to the quality of the cut. Scoring speed and pressure on the scoring tool are controlled in response to the detected sound level. 
     U.S. Pat. Nos. 4,137,803 and 4,204,445 to Goldinger teach a scoring device that will maintain a constant cutting force on a glass sheet despite irregularities in glass thickness or oscillation of the scoring head carriage assembly. 
     U.S. Pat. No. 4,171,657 to Halberschmidt et al. teaches a numerically controlled cutting machine. The cutting head is connected to a pressure control tube which in turn is connected to a hydraulic control device which changes the cutting pressure during the scoring operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cutting assembly which provides quick response for changes in cutting pressure required to optimize the quality of a cut edge. Load is applied to the cutting wheel of the cutting assembly by a primary, constant loading assembly and a secondary, variable loading assembly. In one particular embodiment of the invention, the primary loading assembly is a cylinder which provides a constant load on the cutting head. The secondary loading assembly includes a spring member which, when compressed, transfers the load on the spring directly to the cutting head such that the total force on the cutting head is equal to the primary load plus the secondary load. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation, partly in section and partly cut-away of a cutting assembly, incorporating the present invention. 
     FIG. 2 is a front elevation partly in section and partly cut-away of the cutting assembly shown in FIG. 1. 
     FIG. 3 is a view through line 3--3 of FIG. 2. 
     FIG. 4 is a graph comparing the response time of a pneumatic loading system and an assembly incorporating the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention teaches the scoring of a glass sheet but it should be appreciated that the present invention may be used in any type of cutting operation where quick response to changes in the cutting loads are required. 
     Referring to FIGS. 1 and 2, scoring apparatus 10 is secured to a cutting assembly frame 12 (shown only in FIG. 1). Apparatus 10 includes a cutting assembly 14 having a scoring wheel 16, a carrier 18, post 20 and wheel support and bearing assembly 22 which is mounted on slide 24. Slide 24 is slidably positioned within bearings 26 at the downwardly open end 28 (as viewed by FIG. 1) of cavity 30 in jacket 32. Shaft 34 extends from slide 24 through cavity 30 to a primary loading device 36. Although not limiting in the present invention, in the particular embodiment illustrated in FIGS. 1 and 2, device 36 is a hydraulic cylinder secured to the upper end of jacket 32. When cylinder 36 is pressurized, it provides a constant, downwardly directed pressure through shaft 34 to scoring wheel 16 for scoring glass sheet G. As an alternative, other loading devices, such as a spring (not shown) may be used to provide the primary loading. Support 38 is positioned below the glass sheet G, opposite the scoring wheel 16 to support the sheet during scoring. 
     Apparatus 10 is provided with a secondary loading assembly 40 to rapidly change the load on the scoring wheel 16 in response to changes in the scoring speed so as to maintain the proper scoring depth required to control the cut edge glass quality. Although not limiting in the present invention, in the particular embodiment illustrated in FIGS. 1, 2, and 3, assembly 40 includes collars 42 and 44 slidably positioned about shaft 34 such that the collars 42 and 44 can freely slide along shaft 34 within cavity 30 of jacket 32. Tabs 46 project from between collars 42 and 44 through slots 48 in jacket 32. Gear racks 50 are secured to each tab 46 and are engaged by pinions 52 which are driven by a common drive 54 mounted to jacket 32. Gear racks 50 are oriented such that rotation of pinions 52 moves collars 42 and 44 in a vertical direction along shaft 34 within cavity 30 of jacket 32. Spring 56 is positioned within cavity 30 and captured on shaft 34 between lower collar 44 and the upper end of slide 24, preferably in an uncompressed state, as will be discussed later. If required, a spacer 58 (shown only in FIG. 1) is used to secure spring 56 in position if spring 56 does not extend the entire distance between slide 24 and collar 44. 
     The cutting operation is controlled by a controller 60 which includes the coordinates of the periphery of the glass part to be scored as well as processing routines that process the coordinate data to determine the optimal scoring speeds and associated cutting wheel loading for a particular glass part. In operation, cylinder 36 provides the minimal loading for scoring the glass sheet G when the cutting assembly 12 is moving at its maximum speed. When the scoring speed is reduced, for example to better track the pattern to be scored about a radius, the load must be increased to provide the scoring action required to maintain the desired scoring depth. The controller 60 directs drive 54 to move collars 42 and 44 downward a predetermined distance to compress spring 56. The compression of the spring 56 generates an additional loading that is transferred directly to the cutting assembly 14 as can be seen in FIGS. 1 and 2. The magnitude of the additional loading is determined by the compression of the spring 56. The amount of downward movement of collars 42 and 44 corresponding compression of spring 56 required to provide the additional loading is based on the following equation: 
     
         F=K×(ΔL) 
    
     wherein: 
     F=the additional load 
     K=spring constant 
     ΔL=change in spring length 
     Since the spring 56 is initially positioned within jacket 32 at its uncompressed length, the downward movement of collars 42 and 44 by drive 54 will be equal to ΔL. The load resulting from the compression of spring 56 will be in addition to the primary load provided to the scoring wheel 16 from cylinder 36. 
     Because there is no requirement that the spring 56 be compressed in predetermined increments, the spring 56 can be compressed any amount and therefore the additional loading to the scoring wheel 16 is infinitely variable, limited only by the length to which spring 56 can be compressed. As a result, the precise additional loading required to maintain the desired scoring depth may be provided. 
     As an alternative, the loads from the cylinder 36 and compressed spring 56 can be combined to constantly provide the maximum required scoring load with the compression of spring 56 being reduced in response to changes in the scoring speed to reduce the effective scoring load applied to scoring wheel 16. 
     The present invention provides a fast loading response to the cutting apparatus 10 in response to directions from the controller 60, i.e. the lag time between the signal from the controller 60 to change cutting pressure and the time at which the desired pressure is achieved is minimal. FIG. 4 illustrates the response time required to change the loading on the scoring wheel 16 from a load L1 to L2. Dotted line 62 schematically illustrates the approximate response time for a pneumatic cylinder to pressurize and provide the necessary change in loading and dotted line 64 illustrates the approximate response time for a cutting assembly incorporated in the present invention. In particular, it can be seen that the response time for the present invention of ΔT A  is shorter than the response time for the pneumatic loading assembly which is ΔT B . The delays in the pneumatic system are due in part to the requirement that the system must be pressurized or depressurized with a compressible fluid, for example, air, in order to change the load. In the present invention, the change in loading is directly controlled by compression of the spring 56 and any delays which are due to the activation of drive 54 or gear mismatch between gear rack 50 and pinion 52 are minimal. 
     Based on the teachings of the present invention, it would be obvious to one skilled in the art that the rack and pinion drive arrangement used to move the collars 42 and 44 and compress spring 56 may be replaced with any other type linear actuators, such as, but not limited to, a ball screw or cable and pulley arrangement. 
     Although in the preferred embodiment of the invention, cylinder 36 provides a constant minimal pressure and assembly 40 provides a positive additional pressure in the same direction as the load from cylinder 36, based on the teachings of this disclosure it is obvious that the apparatus 10 can be assembled and controlled so that cylinder 36 provides a constant maximum pressure (corresponding to the slowest scoring speed) and assembly 40 provides a negative load, i.e. a load that opposes the load from cylinder 36 such that the total load on cutting wheel 16 is the load from cylinder 36 less the load from spring 56. With this configuration, the controller 60 would allow spring 56 to remain in its uncompressed state when the relative movement of the scoring wheel 16 is slow and would compress spring 56 to reduce the load from the primary loading cylinder 36 as the scoring speed increases. 
     The present invention provides a scoring apparatus that responds quickly to required changes in loading so as to control the cut glass edge quality. As discussed earlier the controller 60 may be used to determine the necessary changes in cutting pressure during a scoring routine to correspond directly with changes in scoring speed as the glass part periphery is scored. Alternatively, a programmer can direct the controller to change the cutting load at predetermined locations about the part periphery. 
     The form of the invention shown and described in the specification represents a preferred embodiment thereof. It is understood that various changes may be made without departing from the spirit of the invention as defined in the claimed subject matter which follows.