Upgrading Existing Machinery

WEBCON, on the other hand, concentrates on individual machineelements, such as mechanisms (cams, linkages), bearings, drives, etc.The concept is to design a one-for-one replacement with superiormechanical and dynamic characeristics. Such upgrades accomplishthe following:

• Improved functionality
  
• Better product handling
  
• Higher speed capability
  
• Increased reliability
  
• Reduced wear and tear
  

Machine Upgrade 1

WEBCON'S METHOD

Study the Problem:

• Limitations of the current operation
  
• Measure the linkage and the cam
  
• Study other elements of the drive
  

Analysis:

• Prepare Autocad drawings of the existing mechanism
  
• Analyze the motion analytically, graphically and/or by modelling
  
• Modify linkage and drive if necessary
  
• Define parameters for redesign
  

Synthesis:

• Generate the motion using the computerised method below
  
• For cams prepare Autocad drawing and N-C code for milling
  
• Prepare drawings of linkages and drives as needed
  

Support:

• Fabrication support as required
  
• Install and verify
  

CAM DESIGN

WEBCON uses a computerised method for designing cams. It is basedon the synthesizing scheme developed by E.S.Buhayar in his paper"Computerized Cam Design and Plate Cam Manufacture", presented atthe ASME Mechanisms Conference, Oct 1966. The shape of theacceleration diagram is postulated in terms of trigonometricfunctions, and integrated twice with respect to time in order todetermine position.

The following are the noteworthy features of this analytical methodof cam design:

• Flexibility of the shape of the acceleration diagram:

  • parabolic motion (constant acceleration)
    
  • simple harmonic motion
    
  • cycloidal (sine)
    
  • modified sine
    
  • modified trapezoid
    
  • hybrid

• Tabulated moves of the cam follower are directly handled
  
• Motions are prescribed as:
  • dwell
    
  • constant velocity
    
  • acceleration/deceleration
    
  • single lobe acceleration

• Sections of the follower motion diagram are blended together maintaining matching values of the first and second derivatives.
  
• Motion is checked out for:
  • peak accelerations
    
  • jerks

• Five primary geometry schemes convert the developed displacement
  • diagram into cam periphery shape:
    
  • slider, in-line or offset
    
  • swing frame with stroke amplification
    
  • swing frame to connecting rod to slider
    
  • four-bar linkage with stroke amplification
    
  • swing frame to cable to rotary wheel
    
  • output at an angle to the cam plane handled by writing
    
  • special purpose Fortran geometry conversion routines

• Cam shape is checked out for:
  • cam radius for sizing
    
  • cam curvature for undercutting
    
  • torque at the cam shaft
    
  • transmission angle at the cam follower contact point

• Following types of cams can be created:
  • plate or external
    
  • internal
    
  • trapped
    
  • conjugate
    
  • open ended
    
  • track cams

• Offsetting routines develop the trajectory of the cutter center.
  
• Automatic conversion of cam periphery to Autocad script file.
  
• Balancing holes or weights are prescribed for high speed cams.
  

The output of the computer program consists of the following:

• Table of values (usually 360) points for:
  • cam radius
    
  • cam curvature
    
  • torque
    
  • pressure angles

• Autocad drawing of the cam specifying:
  • cutter start and end point coordinates
    
  • material specifications
    
  • machining instructions
    
  • hardening instructions

• N-C diskette for milling (G code) for:
  • x-y coordinates for the milling
    
  • cutter approach and departure moves
    

MECHANISMS

In addition to the 5 basic geometry conversions described in thecam design process, WEBCON has a computer library of frequently usedmechanisms in machine design. These include

• Four-bar linkages
  
• Slider-crank mechanism
  
• Drag-link mechanism
  
• Five-bar with 2 inputs
  
• Geneva-crank mechanism
  
• Epicyclic gear trains

Other linkages are handled by creating dedicated Fortran programs.

The output of these programs are the displacement, velocity andacceleration diagrams. Also outputted are the transmissionangles to check for mechanical efficiency and toggling.

BEARINGS, SLIDES, DRIVES, Etc.

The improvement in mechanical elements is geared towards reducingmaintenance and improving accuracy and reliability of motion.The thrust is towards the following replacements:

• Bush bearings to antifriction bearings
  
• Sliding bushings to ball slides
  
• Chains to synchronous belts

Other mechanical improvements, where applicable, include

• Replacing home-made designs by commercial hardware
  
• Improved wear materials
  
• Centralized lubrication
  
• Ease of adjustments and controls
  

CASE HISTORIES

• The above technology has been used successfully for PCMC Series 150 and 200: Meter winding cams, Latch cut-off cams, and turret indexing ('Web Rewinder Turret Swing Control,' U.S. Patent #4, 265, 409; Cox and Singh)
  
• Perini Model 800 type: Diatrol linkage and cams
  
• Improvements in cams and overhead conveyor of Hayssen (5500 type) increased their speeds from 60-70 to 100 packs per minute.
  
• Improvements in cams and linkages of the Lawton paper wrappers increased their speed from 65 to 105 rolls per minute.
  
• Almost half of the air cylinders in the Europack tray wrappers were replaced with mechanical motions for increased reliability.
  
• The above technology has been applied successfully to create a number of proprietary production machines ('Web Accumulator' U.S. Patent # 4, 009, 814; Singh).