Ken YoussefiMechanical Engineering Dept. 1 Degrees of Freedom Any component that is unconstrained in...

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Ken Youssefi Mechanical Engineering Dept. 1

Degrees of Freedom

Any component that is unconstrained in space has six degrees of freedom.

• Translation – movement along X, Y, and Z axis (three degrees of freedom)

• Rotation – rotate about X, Y, and Z axis (three degrees of freedom)

JointsA mechanism is a mechanical portion of a machine that is responsible for transferring motion, force, and torque from an input source to an output source. A mechanism consists of linkages and joints. Links are considered rigid parts. Joints are movable connections between links and allow relative motion between links.

The Revolute joint (pin or hinge joint) - one degree of freedom

It allows pure rotation between the two links that it connects (R joints)

JointsThe Sliding joint (prism or piston joint) - one degree of freedom

It allows linear sliding between the two links that it connects (P joint)

JointsThe Helical joint (helix or screw joint) - one degree of freedom

The sliding and rotational motions are related by the helix angle of the thread (H joint)

JointsThe Cylindrical (cylindric) joint - two degrees of freedom

It permits both angular rotation and an independent sliding motion (C joint)

Joints

The Spherical (spheric) - Three degree of freedom

It permits rotational motion about all three axes, a ball-and-socket joint (S joint)

Joints

The Planar (flat) - Three degree of freedom

It permits rotational motion about the Z axes axis and sliding motion in x and y axes (F joint), used seldom in design

JointsA cam joint allows both rotation and sliding between two links.

A gear connection also allows both rotation and sliding as the gear teeth mesh

Motion Analysis

In general, there are two types of motion analysis that should be performed to check the design.

Kinematics: deals with the study of motion without regard for the forces that cause the motion. The analysis provides information about the position, velocity and acceleration of all links.

Kinetics: deals with the action of forces on the mechanism. It provides information about the forces at the joints and the required input torque.

Motion Analysis

The process of analyzing the motion of a mechanism.

• Geometric modeling of all parts and creating an assembly model of the mechanism with proper mates.

• Generate the motion model:

Define ground (fixed) components

Define moving components

Define joints and connections

Specify driver(s) component

Specify loads; external loads, body force (gravitational)

• Perform motion analysis

Motion Analysis

• Results visualization (post-processing)

Graphs – study the position, velocity, and acceleration of any link or any point on a given link

Animation – check the overall motion and interference

Prepare reports – graphs and charts

Query – results at specific locations for a given time

AVI and VRML – convert the motion to an AVI or export animations to VRML format for distribution on the Internet

Motion AnalysisTools → Add-Ins and check SolidWorks Motion or COSMOSMotion

2009/102008

Motion Analysis

Motion Analysis combines motion study elements with mates in motion. It also calculates loads that can be used in finite element analysis.

Basic Motion option approximates the effects of Motors, Springs, Collision and Gravity on assembly. This is a physics based simulation

Animation option creates simple animations based on point to point motion of parts in assemblies. Motor could also be used.

Select Motion Study 1

Motion Analysis - Toolbar

No Filter, shows all items

Filter Animated, shows only the moving items

Filter Driving, shows only the items that cause motion

Filter Selected, shows only the selected items

Filter Results, shows only simulated result items

ground

Motor Selection

Select Motor type

Choose the driver, Motion type and specify speed

4-Bar in motion

Results of Motion Analysis – 4 Steps

1. Select a category 2. Select a sub-category

Results of Motion Analysis

Ken YoussefiMechanical Engineering Dept.

3. Select a result component

4. Select a component, 9 in. bar. You can also select a face, an edge, a vertex, or a mate

Plotting the angular velocity of the 9 in. link against the angular displacement of the 2 in. link (input)

Force Analysis

Path Analysis

Disable Orientation and Camera Views

Motion Analysis – Slider Crank MechanismSlider-Crank components, each made in separate files.

Bearing

Slider (piston)

Connecting rod

Assembled Slider-Crank Mechanism

The last mate eliminates rotation and allows only translation between ground (Top plane) and the piston

The first three mates assemble the crank to the fixed bearing and the Right plane

The next two mates assemble the rod to the crank

The next two mates assemble the piston to the pin, allowing the piston to rotate about the pin

Animation WizardCreate simple animations automatically: rotate model about any axis, Explode and collapse model

Animation Wizard

Rotation

Explode

Collapse

Animation Wizard

Fixing or Floating Components in Assembly

“f” stands for fixed component

“-” stands for moving component

Right click the component to change it from fixed to float

2 in link is fixed and 7 in link is the driver

Hinge Mate

COSMOSMotion – Joints, 2007/8 SW

COSMOSMotion

Straight line mechanism

Each rod drawn in a separate file and assembled using various mates. All connections are pin joints (Revolute).

Straight line mechanism

COSMOSMotion - IntelliMotionAt the top of the FeatureManager, select the Motion tab

Select IntelliMotion option

Set units

Select force and time units, mass and length will be set automatically according to your selections

COSMOSMotion – IntelliMotion (gravity)

Specify the magnitude and direction in which gravity acts

This means that a vector of 0,-1, 0 defines the direction

IntelliMotion – Moving and Ground Components

Designate the moving and fixed components

Select and drag over

IntelliMotion – JointsMates specified during assembly will be displayed. You can add or modify joint type.

Linear or torsion spring can be included

IntelliMotion – Motion

Select the driver joint

Select input motion type

Select the velocity function

Specify velocity value

IntelliMotion – Simulation

Select duration and the number of frames.

Start the simulation

Warning – motion not completed due to mechanism discontinuity

IntelliMotion – Animation

Create and save the animation in the AVI format

Check for interference

Motion analysis

Path of any point on the mechanism could be traced

Linear velocity of any point could be graphed

Motion analysis - Velocity

Display the graph

Select component and a point on the component to measure velocity

Motion analysis – Position of ComponentsAn angular displacement between any two components could be plotted.

Motion analysis – Select MotorRotary Motor

Linear Motor

Motion analysis – Apply Forces

Motion analysis – XY plots

Motion analysis – NX5Type of jointsSelect Motion Simulation module

Motion analysis – NX5

First select the Solution and then the Solve option

Potato cutter (french fries)

Main body

Chrome handle

Red slider

Plastic handle

Side bar

Cutting blade

Chrome back plate

Pusher

After creating assembly model, select Motion Simulation module from the Start menu

Assign a driver, right click on joint j006 and select Edit

Select Constant and specify velocity (deg/sec)

Select Driver Type

After assigning the driver, select Solution and then select Solve

Select Animation

Interference Check

Select Type of detection

Select 2nd body

Select 1st body

Just before interference

Check Interference and Pause on Event

Motion analysis – NX5 (example)

Ken YoussefiMechanical Engineering Dept. 1 Degrees of Freedom Any component that is unconstrained in...

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