Objectives Upon successful completion of this lesson, you will be able to:
I Use of a spline curve to control the motor.
I Create a trace path of a point to get the CAM profile.
I Create a SolidWorks part with this CAM profile.
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CAMs SolidWorks Motion can be used to create CAM profiles based on tabular data or input function such as STEP function. We can work backward by driving the follower with the desired motion, then use the motion of the follower to create the CAM profile.
Case Study:
CAM Synthesis
In this case study we will generate a CAM profile based on an input follower
displacement from a data set.
Problem Description
Create a CAM that will move the follower based on the following curve.
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Stages in the Process
To create the CAM, we will follow the steps below:
I Define the motion of the follower.
This can be done from a table of values and drive the follower through a motor.
I Create a Trace Path.
The trace path will be in the exact shape of the CAM surface.
I Export the curve to SolidWorks as a sketch.
The trace path can be imported into SolidWorks as a curve and used in a sketch.
I Extrude the sketch to create the CAM.
1 Open the assembly file. Cam Synthesis.sldasm. Open Cam Synthesis located in the Lesson06\
Case Studies folder.
The assembly consists of a undefined CAM and a follower.
2 Verify the document units.
Verify that the units are set to MMGS (millimeter, gram, second).
3 Create a Motion Study.
Generating a CAM Profile
To generate a CAM profile, the follower motion is prescribed to the path profile while the CAM component rotates 360°. Both are specified in the next two steps.
4 Define a motor to drive the CAM.
Add a rotary motor to drive the CAM shaft at a constant speed of 120 deg/sec. This will rotate the CAM once every 3 seconds.
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5 Examine the profile data.
Open the file CAM Input.xls located in the
Lesson06\Case Studies\CAM Synthesis folder.
Part of the file is shown at right. It consists of X and Y coordinates for the position of the CAM follower.
The file also contains a plot of the CAM profile based on the tabular data. Review it, then close the file.
6 Define a motor to drive the Follower. Add a linear motor to the top face of the
Follower_Guide. Make sure the direction is as shown in the image.
Select Data Points to open the Function Builder window.
Select Displacement for Value (y), Time for Independent variable (x) and Akima for the Interpolation type.
Click Import Data and select the CAM Input.csv file. This file contains just the X and Y data that was in the Excel file.
7 Add gravity.
Add gravity in the negative Y direction.
8 Simulation Study Properties.
Change the study properties to save 100 Frames per second. 9 Run the study.
Run the study for 3 seconds.
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Trace Path SolidWorks Motion allows you to graphically display the path that any point on a moving part follows. This is called a Trace Path and it was already used once in Exercise 3: Trace Path on page 71. In this lesson we will use it to generate a profile of a CAM.
You can select the part that will be used to generate the trace curve by selecting it in the box labelled Select Trace Point Component.
Optionally, you can select a reference component that defines a reference frame for the trace path. The default reference frame is the global reference frame defined by the global coordinate system.
Where to Find It I Create a new plot and select Displacement/Velocity/
Acceleration, then Trace Path.
This field enables you to select a face, edge or a vertex to define a point generating the trace.
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10 Create a trace path which will define the CAM profile.
Click Results and Plots on the MotionManager toolbar.
Select Displacement/Velocity/Acceleration, then Trace Path.
Select the vertex on the Follower-1 to define the CAM profile and the surface of the cam to define the reference component.
Leave the Component to define XYZ directions empty.
Click OK. to show the trace.
Notice how a CAM profile is generated. We will now copy this trace path curve directly onto the
SolidWorks part from SolidWorks Motion.
Exporting Trace Path Curves
Now that we have the shape of the CAM, we can use this path in SolidWorks to create the CAM itself. The trace path curve can be exported to a SolidWorks part.
Introducing: Create Curve From Trace Path
The Trace Path curve can be used to create a curve in a SolidWorks part to create geometry. This can be done in two ways:
I Create curve from path in reference part.
A part already exists, so the trace path curve can be imported to the existing part.
I Create curve from path in new part.
If a part has not been created, it can be done directly using this command.
Where to Find It I In the MotionStudy tree, right-click a Trace Path plot under the Results folder and select Create curve from trace path.
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11 Copy trace path curve to SolidWorks Part.
Right-click the Trace Path plot under the Results folder and click Create curve from trace path, then Create curve from path in reference part.
12 Open the CAM part.
Open the CAM part in its own window.
The curve has been inserted into the part as a new feature.
13 Extrude the profile.
Create a new sketch on the Front plane.
In the SolidWorks FeatureManager, select Curve1.
Click Convert Entities on the Sketch toolbar to project the curve onto the sketch plane.
Also select the outer cylindrical edge of the CAM profile and use Convert
Entities to project this edge into the active sketch.
Extrude the sketch to a mid-plane depth of 50 mm.
Make sure that the Merge results checkbox is unchecked.
14 Save and close the part.
Return to the main assembly.
In the last part of this lesson, we will re-run the simulation with the 3D Contact and verify that the cam profile was generated correctly.
We will need to create solid body contact between the follower and the cam, and drive the motion with the rotary motor on the cam and turn off the linear motor on the follower.
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15 Add solid body contact.
Add Solid Bodies Contact between the follower and the cam. Specify Steel (Greasy) for both materials. Clear Friction. 16 Remove the motion for the follower.
Right-click LinearMotor1 and click Suppress. 17 Add gravity.
Add gravity in the negative Y direction.
18 Motion Study properties.
In the Motion Study Properties, select Use Precise Contact. Whenever we have point contact, we should use precise contact.
19 Run the simulation.
Notice how the follower traverses vertically based on the CAM profile.
20 Examine the motion.
Change to the Back view.
The image is at 1.7 seconds. Notice that the follower is not touching the cam. This separation is the result of the momentum of the follower. Just prior to this time, the follower was driven up by cam. The cam profile requires the follower to change direction rapidly, however the only thing holding the follower in contact is gravity.
Is this a problem? Probably not as the follower will eventually have additional components on top of it to force contact with the cam.
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21 Plot the vertical displacement of the follower-1.
Create a plot of the Y Component displacement of the center of mass of the follower and compare it to the plot in the Excel file. For clarity, the Excel plot has been inverted. Both plots have the same shape.
Cycle based motion
In machine design the independent variable TIME is often not the most convenient choice. It may be more comfortable to design all tasks in terms of one master cycle. Typically, the duration of the master cycle is set to 360 degrees.
Introducing: Cycle Based Motion
Cycle based motion allows user to easily modify the duration of the action, or productivity, in the machine design.
Where to Find It
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Constants and select CycleAngle.
The duration of the cycle is then specified in the Motion Study Properties.
22 Edit rotary motor.
Under Motor Type select Segments to open the Function Builder. In the Function Builder dialog, make sure that the Segments button is selected.
Keep Displacements for Value (y) and set the Independent variable (x) to Cycle Angle.
Add a row and enter 0deg and 360deg cycle angle for the Start X and End X columns, respectively.
Enter 360deg for the final value of the rotational displacement.
Note
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The four graphs indicate the linear increase of the displacement, constant velocity and zero acceleration and jerk.
The 360 degree rotation in 360 degree cycle angle indicates one revolution per output cycle.
Note The duration of the cycle angle (or output cycle) will be specified in the next step.
Click OK to close the Function Builder.
Click OK to save the new definition of the Motor. 23 Study properties.
Set the Cycle time to 3s.
24 Run the simulation.
Notice that the resulting motion of the follower-1 is the same as in the step 21. This is to be expected as both simulation are identical, the former solved using time as independent variable, the later one then using cycle angle as independent variable.
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25 Analyze results.
Notice that the resulting motion of follower-1 is the same as in the step 21. This is to be expected as both simulations are identical the
definition of the independent variable. The former one solved the simulation using time as the independent variable, the later one then used cycle angle.
26 Adjust the cycle time to 1.5s.
27 Run the simulation.
28 Analyze results.
Notice the cam now rotates twice in 3 seconds (study duration).
However, reviewing the trace path we see that follower-1 detaches from the cam - this is unacceptable. The cycle time of 1.5 seconds is therefore too small for this mechanism.
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29 Save and close the file.
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Exercise 10:
Desmodromic CAM
The mechanisms can be actuated and controlled in various directions using various mechanisms. One conventional solution is using springs to return the
mechanism to the original position (i.e. valve springs in engines). An alternative solution may be a system of cams called desmodromic cams.
In the following exercise, we will build a simple mechanism using a traditional torsional spring first. Then we will build a second cam replacing the torsional spring in the system. This way the mechanism will be driven using a system of cams only.
This exercise reinforces the following skills:
I see Generating a CAM Profile on page 167.
I see Trace Path on page 169.
I see Create Curve From Trace Path on page 170.
Project Description
In this project, we have already designed a cam that will drive the link in a predictable motion. As the cam rotates, it will push the link counterclockwise through contact. As the cam continues to rotate, some force is required to have the link follower stay in contact with the cam. In the first part of the exercise, we will apply a torsional spring to the link to keep it in contact.
Spring
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1 Open an assembly file.
Open Desmodromic CAM from the Lesson06\Exercises folder.
The first cam (cam1) is already created and mated to the follower roller1 with a cam mate.
2 Units.
Confirm that the assembly is set to use MMGS units.
3 New study.
Create a new motion study.
4 Restrict axial motion.
The shaft is currently free to move in an axial direction. Add a linear motor to prevent any axial movement of the shaft.
Set the Duration time to 10 s.
5 Add rotary motion.
Add a rotary motor to the shaft to have it rotate 360 degrees in 10 seconds.
6 Cam mate.
Examine the mates in SolidWorks and notice that there is a cam mate between cam1 and the cam follower (roller<1>). While this mate is acceptable for animation, it is unrealistic for analysis because it forces the two surfaces to stay together even if they would not in reality.
7 Run study.
Set the study length to 10 seconds and run it. The study will run and show the motion we desire.
8 Remove the cam mate.
In the FeatureManager design tree, suppress the cam mate.
Note You must return the timeline to zero before suppressing the mate.
9 Run study.
The cam1 still rotates, but the link does not move because there is no connection between the cam1 and the upper follower roller<1>.
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10 Add a spring.
Explode the assembly to make it easier to select the correct surface on the link.
Add a torsional spring to hold cams together.
Use a Spring Constant of 10 N-mm/deg, and 30 degrees for Free Angle. The direction should be clockwise when viewed in the Front view.
11 Add contact.
Apply solid body contact between cam1 and the upper follower roller<1>. For Specify Material select Steel (Greasy) and select Friction.
12 Run the study.
The motion is correct and the design works well at slow speeds.
If we run this system at higher speeds, we could run into a problem where the spring cannot keep the follower in contact with the cam. If we get separation, we could then run into additional problems with the follower bouncing of the cam and getting a motion other than that which we were trying to design.
To force contact, we will design a second cam. When our system is viewed from the Front view, our first cam was able to rotate the link counterclockwise through contact, but clockwise motion depended on the spring. In the next part of this lesson, we will replace the spring with a second cam which will be able to rotate the link in the clockwise direction. The two cams work together to maintain positive contact between the cams and followers.
13 Suppress the torsional spring.
Note You must return the timeline to zero before suppressing the spring.
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14 Delete contact and unsuppress the cam mate.
We are going use the Trace Path function to generate our second cam path. As we need to generate a path that maintains contact throughout the full rotation, we will use the cam mate to force the contact.
Delete the contact between cam1 and its follower roller<1>. In the FeatureManager design tree, unsuppress the cam mate.
15 Run the study.
16 Trace Plot.
Create a new plot to generate the curve of the second cam.
We need to select the center point of the second follower roller. We can do this by selecting the edge of the second follower roller which will define the center point. Also select the face of cam2.
17 Examine the plot.
We now have the basic path, but it is too large because we had to trace the center of the second follower roller<2>. Measure the second follower roller<2>. As it is 52 mm, we will have to reduce the size of the cam2 by half of this, or 26 mm.
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18 Export the curve in the reference part.
19 Open the part.
Open the part cam2 in its own window.
20 Extrude the new cam.
Create a sketch on the Front plane of the part.
Use Convert Entity to create a circle in the sketch based on the outer edge of the existing part.
Use Convert entity again to create a curve from the trace. Set the type of this converted curve to For
construction.
Select the For construction curve
from the trace plot and create an Offset Curve, 26 mm to the inside.
Extrude the new cam2 a depth of 10 mm so that the two solids coincide. Merge the results.
21 Motion Study.
Return to the assembly window.
We will now run the study using the two cams to drive the motion.
Suppress the cam mate.
Add contact between each of the cams and its respective follower.
User Steel (Greasy) for the material and select Friction.
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23 Examine the results.
Both cams stay in contact with their rollers throughout the rotation as one takes care of counterclockwise rotation of the link and the other controls clockwise rotation.
Tip Use a vertical split screen to be able to watch both the Front and Back views as the shaft rotates.
24 Save and close the file.
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Exercise 11:
Rocker CAM Profile
In this exercise we will create a multi-piece cam that is used to control the motion of a slider.
The toothed wheel rotates and has attached to it a drive plate and guides for the slider.
The roller will ride in a path between two stationary cam plates. This system uses the inner cam to move the slider radially outward and the outer cam to move the slider radially inward.
This exercise reinforces the following skills:
I see Generating a CAM Profile on page 167.
I see Trace Path on page 169.
I see Create Curve From Trace Path on page 170.
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Project Description
The assembly rotates at 8,000 deg/sec. On each rotation, the rocker will move radially based on a predefined schedule which is provided in an attached file.
Create the cams from the existing parts based on a predefined motion path provided in the separate file.
1 Open an assembly file.
Open rocker cam profile exercise from the Lesson06\Exercises folder.
2 Examine the assembly.
If we hide the toothed wheel and drive_plate assembly. We can see that the two cam plates are in place, but the cam paths have not been defined.
3 Units.
Confirm that the assembly is set to use MMGS units.
4 New study.
Create a new motion study.
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5 Define the rocker motion.
Add a linear motor to the bottom face of the rocker.
This motion must be specified relative to another component, so select the guide plate (699-0431) shown.
Use Data Points, Displacement and load the file Slide Translation Motion.csv. For Interpolation type, select Cubic.
Make sure that the direction is radially outward.
Make sure that the direction is radially outward.