Globoidal Cam with Indexing Output-Shaft
We can use Machine-Elements toolbar > Add 3D-Cam to model Globoidal Cams.
This tutorial adds the 5 elements you need in the model before we do Add 3D-Cam
Note: Globoidal Cams are also called Ferguson Cams or Roller Gear Drives.
This Tutorial:
1.Add the Cam-Shaft, the Cam-Follower Shaft, the Cam-Rollers, and Cam-Blank Parts and sketches to four different Mechanism-Editors and Planes.
2.Designs and compares the Modified Sine and Modified-Sine Constant-Velocity 33% motions
3.Adds the Globoidal Cam with Add 3D-Cam.
4.Uses the 3D-Cam dialog-box to configure the cam.
5.Exports the 3D-Cam to SOLIDWORKS®.
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Refer to the image: •Cam-Shaft: The input-shaft. It has a Pink-Axis •Cam-Follower: The output-shaft. It has a Red-Axis. It is also called a Turret, or a Star, because the Cam-Rollers radiate from the center of the Star. •Cam-Rollers: They have Green-Axes. The axes are perpendicular(⊥) to the Red-Axis and they radiate from and intersect the Red-Axis •The Green-Axes are on a Plane. The Pink-Axis lies on the Plane that you can construct with the Green-Axes. |
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Commercial Indexing Cams: 'Indexers' Commercial Cam Indexers are nearly always enclosed in sealed, oil-filled cam-boxes. Cam-boxes are often cast, and machined with a CNC machine tool to accurately locate the bearings for the input and output shafts. There is often an eccentric to adjust the position of the output-shaft relative to the input-shaft. Also, there are shims, or other means, to move the cam along its axis to locate it correctly on its shaft. The output is either a shaft, or a flange-plate. The flange-plate may be hollow. |
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Dynamic Considerations Backlash-free, torsionally-stiff couplings are used to connect the input and output-shafts to other parts of the machine. Often, the input-shaft is connected directly to a geared-motor. It is important the motor and gearbox are either connected directly to the input-shaft or as near as possible. It is important that the input-shaft rotates with as near as possible to constant velocity. This is not as easy as it sounds, because the torque as reflected to the input-shaft varies considerably within each index-period. The torque fluctuations referred to the motor can be reduced significantly with a high gear-ratio worm/wheel gearing. With efficient gearing, the motor behaves as a flywheel. If the input-shaft does not rotate at constant-velocity, the motion of the output-shaft will also not follow the indexing-motion exactly. If the motor input-speed varies within a machine cycle, it will be slower than the average when the load inertia is accelerating and faster than the average when the inertia is decelerating. When motor is accelerating and faster than planned, accelerations and speeds of the output-shaft may far exceed those of the original motion-design. When the speed of the input-shaft is faster than planned, it is called 'over-run'. Over-run can damage the Cam-Box, and/or damage your machine that is connected to the output-shaft. Output Exceptions Usually, the output-shaft moves one time (indexes) as the input-shaft rotates one time. The output-shaft may also index two times for each full input-shaft rotation when the index angle is small, and there are many angular movements to do one complete rotation. Read the catalogs carefully. A Cam from Destaco® North America.
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In MechDesigner, a Globoidal-Cam is built on four Planes. We add these elements to the Planes.
The elements on each Plane are easy to add. The skill you will need is to add each Plane correctly. Notes: 1.The image shows the four planes with their names shown SolidWorks®. In MechDesigner, we use the Mechanism name-tabs as the labels for each plane. 2.We only export the 3D-Cam to SolidWorks®. We add the Cam-Follower, the Cam-Roller, and the frame-bracket in SolidWorks® to make an assembly. We can import these SLDPRT models into MechDesigner. |
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STEP 1: Add the Cam-Shaft ( see example: Tutorial 1)
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 MS-CV33 Motion: |
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See image above for the motion Modified-Sinusoid-Constant-Velocity33% See FULL DETAILS : MotionDesigner Tutorials > Tutorial 1 : Indexing Motion In MotionDesigner :
See image below to compare the Peak Velocity and Acceleration Value in a Modified-Sine with those values of the Modified-Sine Constant-Velocity 33% |
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MODIFIED-SINE CONSTANT-VELOCITY 33% (MSC33) In the catalog page, the MSC33 and the MS motion-laws have an Index-Period(β) = 180º. <<< the image shows the Modified-Sine(MS) ( Orange ) AND the MSC33 ( White ) with an Index-Period = 180º.
The advantage of the MSC33 is its low peak velocity, NOT its high Peak acceleration! The advantage of a Reduced Peak Velocity is •Reduced Peak Pressure-Angle •Increased Width of Cam-Ribs |
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When there a small Number-of-Stops, such as four or fewer, the Pressure-Angle can be high and the width of the rib between the cam flanks can be small. To increase the width of the rib between the Cam-Flanks, you can reduce the Cam-Follower Roller diameter, or use a Cam Motion-Law with a Low Constant-Velocity. For information only: Compare the Peak Velocity and Acceleration Values of a Modified Sine Index-Period(β) 180º with those values when the Index-Period is 270º The image compares the two Modified-Sinusoid segments. Orange : Index-Period(β) = 270º , Dwell-Period = 90º Blue : Index-Period(β) = 180º , Dwell-Period = 180º Peak-Velocity : Modified-Sine (β=180º)=~315º/s ; Modified-Sine (β=270º) = ~235º/s Peak-Acceleration : Modified-Sine (β=180º)=~2200º/s/s ; Modified-Sine (β=270º)= ~980º/s/s. Ratios are ~134% Peak-Velocity, ~225% Peak-Acceleration. |
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The output-shaft: 1.The output-shaft is on a different new Mechanism-Editor 2.The axis of the output-shaft is offset from the input-shaft by 110mm. 3.The axis of the output-shaft is 90º , and perpendicular to the input-shaft (Cam-Shaft) 4.The Plane of the Cam-Rollers intersects with the axis-of rotation of the cam-shaft |
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STEP 1: Add a Line to the Base-Part
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STEP 1: Add a Plane to the Line
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 Image of the new Plane - +Z-axis is up. |
Plane •+Z-axis •Origin(0,0) : start-Point of Line STEP 1: Add a Mechanism to the new Plane
You are now in the new Mechanism-Editor. To See kinematic and sketch-elements in each Mechanism-Editor, you must:
The image shows the •Base-Part •Base-Part |
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STEP 4: Add the Cam-Follower to the new Mechanism-Editor (Cam-Follower)
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STEP 5: Add Function-Blocks to plan the Motion of the Cam-Follower
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STEP 6: Edit the Motion-Dimension FB The Cam-Follower (output-shaft) rotates 4 x 90º to rotate a total of 360º. We want to move it in the negative direction.
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STEP 7: Edit the Motion FB
STEP 8: Rename the three(3) elements to Cam-Follower:
MechDesigner will add a number to the end of each new name each time you enter the New-Name. e.g.: Cam-Follower1, Cam-Follower2, Cam-Follower3, ... |
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Note: The Globoidal Indexer is a Body Closed Cam. During its dwell-period, two cam-rollers brace across the cam-flanks on the sides of the cam, to give the Body-Closed construction. Also, a third cam-roller runs inside a groove during the dwell-period. Thus, a total of three cam-rollers are in contact with the cam during the dwell-period - which is over-constrained. The groove for the third-roller that runs in the middle of the cam may be cut wider than the roller during the dwell-period. The L10 life of the roller is longer and it will not scuff the cam surface as much, during the dwell. This cam-follower has eight cam-rollers. They are at equal angles around the cam-follower as a dial, a turret, or a star. We will see we need to add two 3D-Cams to the model. For this, we can add two rollers, or we can design one 3D-Cam with one cam-roller, then move the Cam-Follower to do the other 3D-Cam with the same-cam-roller. It is easier to see with 2 × 3D-cams with two cam-rollers in one model at the same time. We can use a Pattern to show the other 6 cam-rollers. The axis-of-rotation of each Cam-Roller is normal(⊥) to the axis-of-rotation of the Cam-Follower. To add 2 × Cam-Rollers, we must add 2 × Planes that are normal to the Cam-Follower Part. The Planes must at 45º to each other. We will add Lines, and Planes to the Lines, and Mechanism-Editors to the Planes . We will then add the cam-rollers in these new Mechanism-Editors. |
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STEP 1: Add 2 × Lines to the Cam-Follower (output-shaft) (See 3 above)
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STEP 2: Add 2 × Planes to the short Lines
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Note: Plane dialog-box: the order of the X,Y,Z parameter boxes can change! |
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The Blue Z-axes <<< The model after STEP 2. The view shows the edge of the two Planes. They are perpendicular to the Front-View (F3) |
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STEP 3: Add 2 × Mechanism-Editors to the 2 × Planes
STEP 4: Rename elements
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Do STEPS 1, STEP 2 and STEP 3 in Mechanism-Editors Cam-Roller-A and Cam-Roller-B STEP 1: Add a Circle and Profile
STEP 1: Add a Profile/Extrusion for the Cam-Roller
STEP 2: Edit the Extrusion for the Cam-Roller.
STEP 4: Do STEPS 1 -3 again to add the extrusion for Cam-Roller B Notes:
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The Model status (Note: To edit the element colors, use: Application-Settings > Graphic tab > Display colors > Background) Display of Elements
The image shows:
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). We must add a sketch for the Cam-Blank. It is a sketch of the Cross-Section of the steel immediately before the Cams are cut in the steel. In MechDesigner, the Cam-Blank does not move. We must add it to a new Mechanism-Editor. We will add it to the Top Plane, in the Model Editor |
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STEP 1: Add a new Mechanism-Editor to the Top Plane
You will jump to the new Mechanism-Editor. |
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STEP 2: Edit the Base-Part to add the Cam-Blank sketch
<<< The image shows the Front-View (F3) of the Mechanism-Editor (Cam-Blank). Notes: •Cam-Blank must be a sketch-loop. •Rotational-axis - you must add a Line to indicate the rotation-axisof the Cam-Blank. The critical dimensions for the Cam-Blank: A)The Arc should be concentric with the center of the Cam-Follower. B)The radius of the arc should makes sure the top of the cam-rollers are outside the surface of the cam-blank C) The width of the cam-blank should engage with the sides of the cam-rollers in the dwell-period. |
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<< The image shows the sketch of the Cam-Blank with the model and mechanism elements. The Master Machine Angle is set to put the cam-rollers at the end of one index motion cycle. STEP 3: Add a Profile/Extrusion to the Cam-Blank
STEP 4: Edit the Extrusion for the Cam-Blank.
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The image shows the model after we have added the Cam-Blank sketch and a Profile/Extrusion to the sketch. I have used my arrow-keys to spin the model. The Cam-shaft Part is not at 0 to make it easier to see. |
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Add two 3D-Cams. |
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Note: I have made a mistake in the starting-position of the Cam-Follower. Earlier, in the Cam-Follower Mechanism-Editor, we entered Motion-Dimension FB | Base-Value = -135 At this angle, the Cam-Roller is in contact with the Cam-Blank when the Master-Machine-Angle is at 0°. It is much better to edit the Base-Value so that the Cam-Roller moves to enter the Cam-Blank, and then also exit the Cam-Blank later in the machine-cycle. We can correct the error now: 1.Click the Mechanism-Editor : Cam-Follower 2.Edit the Motion-Dimension FB | Base-Value = -90 |
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The image shows the Cam-Follower in the correct position. You must select the Mechanism-Editor Cam-shaft. STEP 1: Click the Mechanism name-tab : Cam-Shaft STEP 2: Prepare the view so that you can see all of the elements you need to select to add the 3D-Cam. •Use the Visibility toolbar > Show other Kinematic and Sketch-Elements •Click in the Selection-Window, then use the up/down; left/right keys on your keyboard to rotate the model-view. << The view of the model should be similar to the image to the left. |
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STEP 3: Click Machine elements toolbar > Add 3D-Cam |
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The Command-Manager needs you to select five elements:
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STEP 4: Add Cam-1: Make the Selections in order, 1 to 5. 1.Select the five elements in order. Refer to the image to the left. 2.Click |
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Q: Why is the 3D-Cam similar to a Worm-Cast (at low-tide on a beach) A: Because we calculate the 3D-Cam (in the same way as 2D-Cams) for the full 360º of the Master-Machine-Angle (MMA). The Cam-Shaft rotates 4 × 360 = 1440° in one Cycle of the MMA. To rotate it four times, we used a Gearing FB and entered Gearing-Ratio=4, as the input to the Motion-Dimension FB. The Cam-Follower also indexes 4 × 90 = 360°. Again, we used a Gearing FB and entered Gearing-Ratio=4 as the input to the Motion FB. Q: Why did we increase the rotations of the Cam-Shaft and the Cam-Follower by four? A: The Cam-Follower must index and move completely across the rotating face of the Cam-Blank. One(1) index-cycle is not enough. Two(2) may also not be enough. Three(3) is usually enough. Four(4) cycles is an insurance policy. |
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Q: How do we remove the 3D-Cam data that we do not need to calculate the flanks of the 3D-Cam? A: Use the 3D-Cam dialog-box... Cam tab > Flank-Length STEP 1: Edit the 3D-Cam 1.Click the 3D-Cam element in the graphic-area or the Assembly-Tree 2.Right-click the 3D-Cam element in the Selection-Window 3.Click Edit element in the contextual-menu The 3D-Cam dialog-box will open. The 3D-Cam dialog-box has three tabs: •Cam / Display / Export |
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STEP 2: Click Cam tab: Flank-Length The angles are the limits of Master Machine Angle over which we calculate the 3D-Cam 1.Start Angle 2.End Angle |
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When you add a simple extrusion, it is easier to see where the 3D-Cam-Track and Cam-Roller enters and exits the Cam-Blank. << here, there is a simplified Cam-Blank - an Extrusion of a Circle on the Cam-Shaft Start Angle = 15 End-Angle =120 |
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STEP 3: Add Cam 2 Prepare the View again : 1.Visibility toolbar > Show Solids in Mechanism - to hide 2.Click the Selection-Window, then use the arrow-keys on your keyboard to rotate the model to see all 5 elements you must click to add the 3D-Cam. Add 3D-Cam 2 3.Click Machine elements toolbar > Add 3D-Cam 4.Click again the 5 elements 5.Click |
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6.Open the 3D-Cam dialog-box 7.Edit the Display tab : Display in Graphic-Area > color to choose a different color for Cam-2 8.Edit the Cam tab : Flank-Lengths. Start Angle = 30 End-Angle =200 Explore the different parameters in the 3D-Cam dialog-box. Close the 3D-Cam dialog-box or see below: 9: Export the 3D-Cam to SolidWorks |
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We recommend in MechDesigner 14 and later releases, you follow these instructions. Start SOLIDWORKS®: 1.Start a new SLDPRT part document 2.Save the Part as an empty file. In MechDesigner : 1.Edit 3D-Cam Cam-1 to open the 3D-Cam dialog-box. 2.In the Export tab: SolidWorks Data-Transfer > Send Cam-Blank In SOLIDWORKS®: The Cam-Blank should be in the SOLIDWORKS® part document ( see MechDesigner > 2) 1.Save the Cam-Blank document as e.g. Cam-Blank.SLDPRT. Do not close it. |
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MechDesigner : Make sure you have entered the Parameters as required in the 3D-Cam-dialog-box 1.Click the Rebuild button, at the top of the dialog, to apply the latest parameter values 2.Click the Save button. In the Windows® dialog: 3.Select Save as Type > STEP file-type, enter a file-name (e.g. Cam-1), click the Save button 4.Close the 3D-Cam dialog-box Do 1 - 4 again. to edit and save Cam-2 as a STEP file-type. SOLIDWORKS®: 1.Do File menu > Open> STEP file-type > Cam-1 (see 5 above) It may be necessary to: a.In the Feature-Manager: Right-Click Cam-1 b.In the contextual-menu, click Dissolve Feature , and Yes, break the link c.In the Feature-Manager: Right-Click Surface-Imported1 d.In the contextual-menu, click Import-Diagnostics, in the Import-Diagnostics Property-Manager click the Attempt to Heal All button, and then 2.Save Cam-1 document as Cam-1.SLDPRT file-type. Do not close it. Do 1 and 2 again to save Cam-2 as Cam-2.SLDPRT. Do not close it. |
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Return to the Cam-Blank SOLIDWORKS® part document. Then do: 1.Insert menu > Part... and Cam-1 as the Insert Part document The 3D-Cam should be in the correct physical location. You should be able to: 2.Click 3.Insert menu > Part... and Cam-2 as the Insert Part document 4.Again, click |
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Finally: 1.Do Insert menu > Feature > Combine, and use subtract radio-button. 2.As the Main Body select Cam-Blank 3.As the Bodies to Combine select Cam-1 and Cam-2 You should now see the tracks of Cam-1 and Cam-2 in the Cam-Blank. |
STEP 1.Open the 3D-Cam dialog-box and Edit the 3D-Cam settings: 1.Double-click the 3D-Cam in the graphic-area. The 3D-Cam dialog-box should open. If the 3D-Cam dialog-box does not open, then we recommend this method: 1.Click the 3D-Cam element in the graphic-area or the Assembly-Tree 2.Right-click the 3D-Cam in the Selection-Window 3.Click Edit element in the contextual-menu The 3D-Cam dialog-box will open. The 3D-Cam Separators
STEP 2.Send the Cam to SOLIDWORKS See 3D-Cam dialog-box: Cam Transfer |