NX Motion Simulator

Fachgebiet Maschinenbauinformatik - Bergische Universität Wuppertal

CAD knowledge base 2011 1 NX Motion Simulator

Fachgebiet Maschinenbauinformatik

Modeling and Kinematic Simulation of the linkage Ko-U-02

Christian Bartschies Matrikelnummer 824570

Translated by Narendra Komarla

Matriculation number 950763



Contents

1. Objective ....................................................................................... 03 2. Basics of handling NX 7.5 ........................................................... 04 3. Modeling of the components 3.1. Modeling – Base-plate ...................................................... 05 3.2. Modeling – 50mm Link ..................................................... 08 3.3. Modeling – 75mm Link ..................................................... 08 3.4. Modeling – 100mm Link ................................................... 09 3.5. Modeling – Slotted bar, 200mm ........................................ 11 3.6. Modeling – Rod ................................................................ 13 4. Creating the assembly ................................................................. 14 5. Kinematic Simulation – The motion simulator 5.1. Creating the Kinematic-Simulation ................................... 17 5.2. Creating graph plots ......................................................... 26 5.3. Dynamic distance and angle measurement ...................... 29 5.4. Interference check ............................................................ 32 5.5. Tracing the simulation ...................................................... 33 5.6. Recording the simulation .................................................. 35 6. List of NX functions used ............................................................ 36



1. Objective The following Documentation describes the creation of the individual components, assembly and the Kinematic-motion simulation of the linkage Ko-U-02 with the help of various commands in NX. The document is a detailed report explaining the commands and the options used in the software.



2. Basics of handling NX 7.5 Before the Kinematic - Motion Simulation could be started, the following settings have to be made in advance. For complete menus to be available throughout the work, a role with “Advanced with full menus” has to be activated. This can be achieved from the “Roles” menu available in the home page of NX. The menu and toolbar customization will be overwritten once this option has been used.



3. Modeling of the components 3.1 Modeling – Base-plate

In order to create new components, “New” has to be selected from the main menu. The window as seen in the figure below is opened. The template “Model” is selected from this window. The component name and the path are then confirmed with the “OK” button.

There are several possibilities for creating a new part. The first method is based in the fundamental approach of constructing a sketch. The base plate is constructed in

this approach. A new sketch can be created by selecting “Sketch” from the icons, or can be inserted from the main menu (Insert > Sketch). In this example, the YZ plane is selected. Once the plane is selected, it is displayed in the sketch window. The selected plane is highlighted in blue and the view is isometrically oriented at this point of time. Simple and quick sketches can be sketched in this orientation itself. However, when the sketches are a bit more complex, it is recommended to be sketched in the orthogonal orientation. This can be achieved using the “Open in sketch task

environment” icon. There are additional options available for the sketch. Other orientations can also be achieved using the orient option as seen in the picture below



The base plate is created by creating a rectangle in the first step. The “Rectangle”

button give further options (by two points, three points or by the center) to create one on the sketch plane. The “Two points” option is selected as it is the most common method. The sketch created is dimensioned automatically. However, it is better to right click on the dimension and convert it to a “Driving dimension”. These dimensions are adjusted accordingly. The edges of the plate are rounded using the

“Fillet” option. Two lines have to be selected to create a fillet between them. The radius of the fillet is dimensioned automatically, but however, they are converted into driving dimensions later. The sketch looks as seen in the picture below. The radii are then adjusted to the required value by a double mouse click on the dimension.

Once all the dimensions have been adjusted the button “Finish sketch” will exit the sketch dialog.

To create a volume model, the “Extrude” option is selected (which can be found in the “Feature” menu). The extrude window opens.



The new sketch is created on the top surface of the base plate. Once this sketch is created and constrained completely, it is ready for the subtract operation. The

“Extrude” command is again used for this. The additional feature created should

be subtracted from the first solid by using the Boolean operation “Subtract” . The material removing technique is analogous to the manufacturing procedure. The first part is completed with this operation.

Under the menu, “Section” the sketch which has to be extruded is selected. The direction of extrusion can be selected from the “Direction” option. In this example, the default values are retained. The thickness of the base-plate is 8mm. This is input under the “Limits” menu. The window is then exited by the “OK” button. The volume model now appears on our screen.



3.2 Modeling – 50mm Link The next part to be modeled is a link with two holes.

A rough sketch is made using the “Profile” command by drawing a horizontal line. For creating the round, we can change the “Object type” from “Line” to “Arc”. The object type is again changed to line to draw another horizontal line and changed back to arc finally, to complete the profile.

The holes are sketched in the same sketch using two “circles”

The default option of creating a circle with “Center and diameter” is used in this case. The feature allows the user to specify a point, which would be its center and then create a circle with the require diameter. When the mouse is held at an approximate point near the center, the actual center of the required circle is automatically detected. The diameter of the circle can be adjusted and converted into a driving dimension later. Once the sketch is finalized, it is extruded similar to the first model, but with a thickness of 5mm. 3.3 Modeling – 75mm Link

The next component is a similar link, with a different overall length. An alternative way of modeling this component is presented here.

A rectangle is created in the first step, using a rectangle command, which is already familiar to the user. The dimensions of the rectangle are fixed. Once the sketch is extruded to the required thickness, the edges are blended using the “Edge

blend” option. The window seen below opens for edge blend.



The radius is input and the edges are selected. In this example, all four edges are selected and the radius is input as 10mm. NX preview enables the user to visualize how the model looks once the operation is completed.

The two holes are then created in similar fashion as before. 3.4 Modeling – 100mm Link The next model is another link with a different length. This gives an opportunity to model this component in another style, which is demonstrated here. Volume elements can be created in NX without creating sketches, this can be found under Insert > Design Feature > ….. For creating this link, a block is used. This block feature prompts the user to input parameters as seen in the picture below.



The edges are blended similar to the previous model.

The holes are created using “Hole” feature. The window seen below opens for the hole feature.

As “Type”, the default option of “Origin and Edge Lengths” is used. The “Origin” of the block is the origin of the co-ordinate system (WCS) by default. However, this option can also be changed as per requirement.

In this window, the user has the possibility to create holes in different styles. The default Type, which is a “Central hole”, is used in this example. It is required to fix a position for the hole on the surface of the solid.



3.5 Modeling – Slotted bar, 200mm The “200mm lever” is again identical to the previous three parts. In the process of creating this part, geometric constraints, which can be used to create fully constrained sketched are demonstrated. Once a new sketch is inserted in a selected datum plane, it is oriented orthogonal to

the viewing place using “Open in sketch task environment” The options exclusive

to a sketch are activated with this. The “Automatic dimensioning” is turned off in

this example. The first step is to construct a “Rectangle” .The rectangle has to be so placed, that its center point should be located at the origin of the co-ordinate

system. This is done by using the option “Symmetry” . Once the symmetry option is selected, the following window opens:



Once the rectangle is rendered symmetric about the co-ordinate axis, a “Circle” with three points is constructed. The center of the circle must lie on the horizontal axis. The circle is constructed approximately at the first instance. To ensure that the circle lies exactly on the line, a constraint has to be specified. The user has to click

on the icon “Constraints” (alternatively also the key “c” on the keyboard). Once the “Constraints” button is clicked, the form of the cursor changes (Cursor with constraint form). The user is required to click on the center of the circle now, which opens a small “Constraints” window, indicating the possibilities of constraining that circle. The horizontal axis of the co-ordinate system is now selected. On selection, the Constrains automatically change, with new entries, such as “Point On Curve”, “Midpoint”, etc. In this example, the “Point On Curve” option is chosen.

The step is repeated with for all three circles. As before, the “Continuous automatic dimensioning” was turned off. The other dimensions are specified manually. The dimensions of the holes have to be specified as 8mm. This is done using the

“Inferred Dimensions” option. The specific dimensions (Like horizontal, vertical, parallel) can be used directly, from the small drop down arrow present in the “Inferred Dimensions” icon. These are used only when it is not possible to dimension directly using the “Inferred Dimensions”. Once the hole is dimensioned, the sketch is fully constrained. It can be extruded into a volume body, as illustrated in the previous examples.

Under the menu “Primary object”, the first horizontal line of the rectangle is selected. In the “Secondary object”, the second horizontal line (The line below) is selected. As the “Symmetry center line”, the horizontal axis which is located at the center is selected. This would make the two horizontal lines symmetric about the axis. The same is repeated for the vertical lines too.



3.6 Modeling – Rod This component is created using a sketch.

The sketch is extruded to a thickness of 6mm. A hole at the center, with a diameter of 8mm is created. The hole can also be included in the sketch.

Note: The modeled components may be colored differently for better clarity. This can be done by “Edit” (Right mouse click)

(The whole component must be selected. “QuickPick” can be used). For precise selection, the “QuickPick” Menu can be used. When the user waits for 2-3 seconds before the mouse click, the cursor changes its form (three dots precede the cursor). Upon a mouse click now, a new window appears with a list if selection possibilities for the user. Precise selection may be made through this list.



4. Creating the assembly To create the required assembly, the individual components are loaded into a new environment, where they are assembled. The assembly module is available through the main menu. A new “Assembly” is created as seen below.

The assembly data can be named appropriately. The window is closed by confirming “OK”. A new window opens at this stage. Using the options in this window, all parts which are supposed to be a part of this assembly can be selected. A mouse click on “Open” browses through the computer storage, from which the individual components are selected and loaded into the new environment. The window is closed with the “OK” button



The components of the assembly must be positioned appropriately. This can be done by selecting one of the planes in the co-ordinate system. Then, the window is confirmed and closed through “OK”. It is now seen that all the components of the assembly lie in one plane. To distinguish these parts and to move them in space, the

command “Move Components” is used.

Subsequently, more components may be added using the “Add Components”

command.



The assembly is constrained using the “Assembly constraints” . The completed assembly looks as seen in the picture below:

The “Move components” window allows the user to select the component to be moved. When the Transform Motion option is set to “Dynamic”, the components can be moved with respect to the selected co-ordinate system.



5. Kinematic-Simulation – The motion simulator

5.1 Creating the Kinematic-Simulation Some pre-settings have to be done before the kinematic-simulation could be started. The assembly, which was created in the previous steps, is loaded first. The environment is changed to kinematics through the main menu, “Start”.

The kinematics module in NX is called “Motion Simulation”

The user has to Right click on the loaded assembly and select a “New Simulation”. A new window “Environment” now opens.



At this point of time, the “Motion Joint Wizard” will prompt the user if the constrains have to be transferred from the assembly. For the purpose of getting familiar with this workbench, it is recommended to cancel this operation. The constraints can now be redefined.

A new simulation “motion_1” is thus created as seen in the picture besides

The analysis type is selected in this window as “Dynamic”. The dynamic analysis type is confirmed with the “OK” button.



As the first step in motion analysis, the “Links” must be defined. Defining the links allows the user to set which parts of the assembly should have movement. This is one of the important requirements to construct the motion model.

Three more links are now defined. The part “link_75mm” is defined as the second link and the part “link_100mm” is defined as the third link, with appropriate names. The model tree now looks as seen below:

The subsequent step is to define “Joints” , which simulates a rotating motion in between these links. A joint describes the relative movement of bodies, relative to the other. A mouse click on the “Joint” button opens a new window, which looks as seen in the picture below.

A click on “Link” option opens a new window as seen in the picture besides. The user can select one or more objects from the assembly. If more than one component is selected as a link, they always move together in the simulation. In this example, the “base_plate” and the “link_50mm” are selected. The selection can be made by a direct mouse click on the component, or through the model tree. A meaningful name is given to the created link, to facilitate further changes, which are in-evitable. A mouse click on “OK” would confirm the actions and the link appears in the model tree.



Under the Menu “Base”, the base link has to be selected. The base link has to be connected with the “Joint”, which is created in the first step. The appropriate link is selected, which is “Link_100mm”. The same is step is repeated for the other links too. Hence four joints are created, which appear in the model tree, as seen in the picture below.

Under the “Type”, the type of joint is selected, in the first instance; a

“Revolute” joint is defined. Under “Action” menu, the connecting body movements have to be defined. The body has to be selected as a whole. It is in our example, the edge of the hole left by the component “link_50mm”. For precise selection, the “QuickPick” Menu can be used. When the user waits for 2-3 seconds before the mouse click, the cursor changes its form (three dots precede the cursor). Upon a mouse click now, a new window appears with a list if selection possibilities for the user. Precise selection may be made through this list.



If the visual appearance (symbol) of the joints is very small, the scale can be increased through “Preferences > Motion”, where the value of the “Icon scale” can be increased from the default value of 1.00 to 5.00 (as an example)



It is recommended to save the simulation at this stage using the “Save” command. Once the links and the joints have been defined, the system must be informed as to which parts should remain stationary (fixed). In this example, the “Base_plate_link_50mm” is fixed by a right mouse click on the link, and selecting “Fix the link”.

The motion simulator now requires a “Drive”. Gravity can be a driver at the first instance. The acceleration due to gravity can be simulated and for this purpose, the



direction of the gravity must be input. This is done as follows: Preferences > Motion > Gravitational constants and input the value Gz = -9806.65, for defining the acceleration due to gravity in the negative “Z” direction.

The button “Solution” (Which is a command in the motion menu) is clicked upon. The following information window opens:

With the command (button) “Solve” the entries are calculated. An information window appears indicating the redundant degrees of freedom (or constraints). A redundant constraint means that the degree of freedom of the system is over-determined. The over-determination of complex assemblies can lead to conflicts. To make sure that we arrive at a conflict-free solution, these provisions are eliminated automatically by the motion analyzer.

As solution type, the “Normal Run” is selected and as the Analysis type, “Kinematics/Dynamics” is chosen. As an example, the “Time” is input as 2 seconds and the number of “Steps” is defined as 100. All parameters are confirmed with “OK”. The motion navigator in the model tree will now have a new entry “Solution_1”, with relevant sub-entries.



Changes may be made for the simulation. Right mouse click > “Edit” , the joint

type for “J003” is changed from “Revolute” to “Spherical” . The joint type of

“J004” from “Revolute” to “Cylindrical” . After this change, the system must be

re-calculated (“Solve” ).

The simulation cannot be started with the “Play” button at this stage, since the system still does not have a “driver” (excluding gravity), it just oscillates under gravity.

The animation can be stopped using “Finish animation” . Right mouse click on “motion_1”, Information > Motion Connections provides information relevant to this simulation. One of the important information listed here is the number of degrees of freedom. In this example, the system should have one degree of freedom, which is rotation. The animation shows clearly that the mechanism can rotate around the axis. A “driver” has to be added for the mechanism for complete rotation. This is done by right click on the first joint, “J001” and “edit”. The tab “Driver” in the menu is selected. At this point of time, the driver is “None”. The dropdown menu has other options, where “Constant” is selected.

The system has to be calculated with the new parameters using “Solve” ). The animation can be started with “Play” . Our animation is controlled using the “Animation Control” menu, as seen below.

The “Initial velocity” is set to 360 deg/sec. The “Constant rotation” executes a simulation with constant motion and acceleration with respect to time.



If the animation ends too quickly, the “Animation” button has options, where it could be controlled. To slow down the animation velocity, a higher value (for example 50) for the “Animation delay” could be given. Other options include “Play

once” , which would run the simulation only once. The option “Loop” allows the user to view an endless animation and the option “Retrace” runs the simulation once forwards and once backwards respectively. Once the settings are entered as required, they are confirmed and the window is closed with “OK”. The animation can now be started with the “Play” button in “Animation Control” as discussed before. Once the simulation meets all requirements as desired, it can be terminated with

“Finish Animation”



5.2 Creating graph plots

A useful tool in Kinematic simulation is the creation of graphs. The advantage of graphical notation is that the designer can get a quick overview and make necessary changes.

The function “Graphs” will now be demonstrated using the angular variation of “Joints”.

The “Graphing” icon can be found in the

“Animation” pull- down menu . A mouse

click on the option “Graphing” , opens the graphing window.



The window is closed and parameters are confirmed, with the “OK” button. We immediately get a graph, which looks as seen in the picture below.

The user would be prompted to select an object, which is “Joint-J004” in our case. In the request field, “Displacement” is selected. Under component, “Euler Angle 1” is selected. The option is set to “Relative”. The parameters chosen

are input using the “Add on curve” option. (The “Relative” option allows the change in viewing angle. The “Absolute” option is based on the co-ordinate system in the joint Optionally several “Joints” can be supplemented with different

settings



The user can leave the “Graphing” module using, “Return to Model”

There is a possibility to re-use the function “Play” . It is difficult to clearly spot the displacement with respect to a particular time instance. To read the values clearly

from the graph, the “Probing Mode” could be used, additionally the option “Peak-

Probing Mode” could also be used, where the extreme values could be read easily. If the measurement of the data was successful, the graphing environment is

abandoned through the option, “Return To Model” . However, the data can be accessed through the model tree at any instance. On using the function “Return To

Model” , it is sometimes observed that the previous animation does not work

anymore. When the “Play” button is pressed, we get the following information window:

When the animation is not active in the model tree, or when there is no animation created, the warning message as seen besides is displayed. This situation can be set right by double mouse click on the “Animation” in the model tree (in this example “Solution_1”) this opens a window, which can be directly closed with “OK”. The animation works normally now (as before).



5.3 Dynamic distance and angle measurement Often, it is useful to measure the dynamic change in distance or the angle of the linkage. This may be of special interest during a collision. The following description demonstrates the usage of this option.

The command “Measure” (NOTE: Not to be mistaken with “Measure distance”

) opens a new window. The “Measure” command may be found in the “Interference” menu

The solution which was created in the previous steps is now revised. Double mouse click on the “Solution_1” in the Motion-Navigator opens the solution window as seen in the figure besides. A new value for “Time” is keyed in as 1, and the value for “Steps” to 360. The window is closed with “OK” and the solution is re-calculated using

“Solve” . Alternatively the user can retain the previously selected values, but the resulting numerical values may be inaccurate.





The “Type” is chosen as “Minimum distance”. The function “Angle” can be chosen when we need the dynamic measurement of an angle. We must now select two objects, between which the measurement has to be made. As seen in the figure, for this example, each of the lateral surfaces of two holes for the “First set” the lower-left and for the “Second set” the upper right area. (Order of selection does not influence the result). For dynamic measurements to be visible, it has to be activated in the “Animation”. It can be seen in the picture below that “Measure” has been activated. The dynamic distance between the selected holes is seen in the other picture. A ruler appears on the screen, which aids the user. In case of dynamic angular measurement, a protractor appears on the screen. The dynamic measurement created is automatically located in the “Motion navigator”. The name is “Me001” in our case, which is a default first name for a new measurement.

If two such points should be considered, which cannot be detected through the existing geometry, they must be added subsequently to a measurement that can lead

to (eg: “Marker” ). The user should have set the type to “Spot”, and then the edges, which should be observed must be selected. Under “Settings” the user can enter a different value for “Threshold”, example a value of 50. The “Measure condition” to “less than” and the tolerance to “0.01”. With these settings, the simulation can be automatically stopped when the threshold is reached.

The “Pause On Event” option is activated in the “Animation” (at the bottom of the window).

The window is closed with “OK”. The animation is started using the “Play” . An example, where the simulation stops at a threshold of 50, gives the message as seen in the picture above. If new dynamic measurements have to be created, the first measurement “Me001” can be de-activated, or deleted from the “Motion Navigator”.



5.4 Interference check UGS NX 7.5 has extra features, which allows the user to determine interference between two components. Interference can be analyzed using the dynamic distance and angle measurement as illustrated in the previous section. However, detection using the dynamic distance measurement is not the best way to ensure it. Therefore, for our present analysis, an additional protruding cylinder is modeled to demonstrate this feature.

In the function “Animation” the option “Interference” had to be activated. Once

the solution has been re-calculated (“Solve” ), the animation is started as in the

previous examples with the “Play” button. It can be viewed that the animation flashes, during collision. Optionally, the user can check animation by “Stop on collision” option too. When this option is activated, the following information is displayed in case of collision.

Another possibility to demonstrate collision is using the “Section curve” option.

In this option, the border lines of the intersecting parts are highlighted in red.

This option required the “Pause on event” option to be activated in “Animation” . With a double click on the interference entry “In001”, in the model tree, this option can be selected. The other options remain the same. Playing the animation using

“Play” would now highlight the areas of intersection in red color. The third alternative to check for interference is by creating an interference solid

“Create interference solid” . The following simulation now indicates the volume to be cut. It should be noted that the appropriate components are selected in the “First Set” and the “Second Set”. If the user notices that the wrong parts have been selected, the generated volume will be deleted. The cursor must be kept on the volume until it changes (with three preceding dots). When the cursor is clicked now, the “QuickPick” menu opens as seen in the picture below.

With the function “Interference” we have a new window, which can analyze the interference, if present.

The type “Highlight” is chosen. Under “First and second Sets” the components which have to be analyzed have to be selected. In this example, the “Cylinder” (which is purposely modeled on the base-plate) and “Link_200mm” are chosen. The window is closed with “OK”.



5.5 Tracing the simulation Siemens NX 7.5 has possibilities to generate images at each step of the simulation. (Generates images of one or more components of the assembly).This option can be loaded into the design environment by the user, where they are processed further. To

use this function, the button “Trace” is used. In the newly opened window, one or more objects can be selected, whose path has to be traced. In this example, the “Link_200mm” is selected. The result of this function can be represented. The trace

function must be activated in “Trace” under “Animation” (other picks can be

removed). A mouse click on “Play” starts the simulation creating solid body trace. It is suitable for reduce the increment of “Solution_1”, In the model tree from

360 to around 50. The linkage is solved again (“Solve” ) which is necessary. Once complete, the trace of the link appears as seen in the picture below:

The “Construction objects” option is selected, followed with a right mouse click, so that the whole group is selected. The group can be deleted.



To return to the original presentation, we must use the “QuickPick” – Menu again. We can right-mouse click on the group and “Hide” can be used to hide the whole group. Alternatively, the entire application can be undone. This is easily done by pressing on

the “Undo” button, or “Strg+z” using the keyboard.

By changing the construction environment, these newly produced solids are processed. As before, the entire group can be selected (By right mouse click) and using the “QuickPick” menu and “Copy” is selected. Subsequently, a new “Model” can be created to “Paste” the result there. The new model represents the trace of “Link_200mm” in our case.



5.6 Recording the simulation

In this chapter it is demonstrated how generated simulations could be combined into

one video. With the right-click on the created simulation, “motion_1” > “Export” >

“Mpeg” , a new window is opened.

Sometimes, it is more advantageous to record movie files as desired. The work area is directly recorded in this case, and the user has complete control. The following is the process for such recording:

“Tools” > “Movie” > “Settings”

In the field “Capture area”, “Desktop” in chosen and a desired value for “Speed” is also specified. The window is closed with the “OK” button. The recording can now be started with the shortcut “Alt+F5” or “Tools” > “Movie” >

“Record” . A new window opens, which prompts the user to specify the path. The save path is confirmed with “OK”. The “Desktop-recording” thus begins and the video will be added at every step. All desired steps can be included. With the Shortcut “Alt+F7” or

“Tools” > “Movie” > “Stop” , the recording can be stopped at any instance.

In the new window the file name is entered in “Specify File Name” and the location for saving the file is specified. Subsequently, the window is closed with “OK”, and subsequently, the video is saved in the specified location. A useful tip during recording a video is to fit the assembly into the screen and then record.



6. List of NX Functions used

Function Page No.

"New" 05

"Sketch" 05

"Orient" 06

"Open in sketch task environment" 06

"Rectangle" 06

"Fillet" 06

"Finish sketch" 06

"Extrude" 06

"Extrude" (Boolean Operation) 07

"Profile" 08

"Circle" 08

"Rectangle" 08

"Edge Blend" 08

Design feature "Block" 09

"Hole" 10

"automatic dimensioning" 11

"Make symmetric" 11

"Constraints" 12

"Inferred Dimensions" 12

"Point on Curve" 12



"Edit Display" 13

"Move Component" 15

"Add Components"

15

"Assembly Constraints" 16

Kinematics: Start > Motion Simulation (Functions only, when the assembly module had been started).

17

"Link" 19

"Joint" 19

"Revolute" 20

"QuickPick"- Menu 20

"Icon Scale" 21

"Save" 22

"Fix the link" 22

"Solution" 23

"Solve" 23

"Edit" 24

"Spherical" 24

"Cylindrical" 24

"Finish Animation" 24

"Animation" 25

"Play once" 25

"Loop" 25

"Retrace" 25



"Graphing" 26

"Add one curve" 27

"Probing mode" 28

"Peak – Probing Mode" 28

"Return to Model" 28

"Measure" 29

"Measure Distance" 29

"Marker" 31

"Interference" 32

"Highlight" 32

"Show Intersection Curve" 32

"Create Solid" 32

"Construction Objects" 33

"Trace" 33

"Undo" 34

"Export" 35

"Mpeg" 35

"Settiings" (Movie) 35



"Record" 35

"Stop" 35

Documents

NX Motion Simulator