Tài liệu Exercise Machine Repeated Assembly Analysis docx

You can add a servo motor to a joint axis or a geometric entity, such as part planes, datum planes, and points.. You can use the following types of servo motors: • Joint Axis Servo Motor

Exercise Machine Repeated

Assembly Analysis

ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN

Exercise Machine Repeated Assembly Analysis

Pro/ENGINEER Wildfire 2.0 - MECHANISM

Dr Herli Surjanhata

Servo Motors

Servo motors are used to impose a particular motion on the

of freedom You can add a servo motor to a joint axis or a geometric entity, such as part planes, datum planes, and points

You use servo motors to impose a particular motion on a mechanism Servo motors cause a specific type of motion to occur between two bodies in a single degree of freedom You add servo motors to your model to prepare it for analysis

Servo motors specify position, velocity, or acceleration as a function of time, and can control either translational or rotational motion For example, a servo motor starts in a specific configuration After one second, another configuration is defined for the model The difference between the two configurations is the motion of the model

By specifying your servo motor's function, such as constant or ramp, you can define the motion's profile You can select from several

predefined functions, or input your own function You can define as many servo motors on an entity as you like

Note: If you select or define a position or velocity function for your

servo motor profile that is not continuous, be aware that it will be ignored if you run a kinematics or dynamic analysis However, you can use a discontinuous servo motor profile in a repeated assembly

analysis When you graph a discontinuous servo motor, Mechanism Design displays messages indicating the discontinuous points

You can place servo motors on joint axes or on geometric entities such

as part planes, datum planes, and points You can use the following types of servo motors:

• Joint Axis Servo Motors—Use to create a well-defined motion

in one direction

• Geometric Servo Motors—Use to create complex 3D motions

such as a helix or other space curves

Force Motors

Geometric Servo Motors

If you select points or planes to define the servo motor, you are

creating a geometric servo motor Use geometric servo motors to

create complex 3D motions such as a helix

If you select Point or Plane, you must also select a point or plane as

a reference

If you select a point for the reference entity, you must also select a motion direction

You can create the following geometric servo motors:

• plane-plane translation servo motor

• plane-plane rotation servo motor

• point-plane translation servo motor

• plane-point translation servo motor

• point-point translation servo motor

REPEATED ASSEMBLY ANALYSIS

Repeated Assembly analysis was called Kinematic analysis in previous releases of Mechanism Design It is a series of assembly analyses

driven by servo motors Only joint axis or geometric servo motors can

be included for repeated assembly analyses Force motors do not

appear in the list of possible motor selections when adding a motor for

a repeated assembly analysis

Note: If you edit an analysis that you created as a Kinematics analysis

in a previous release of Mechanism Design, the definition will now specify it as a Repeated Assembly analysis

A repeated assembly analysis simulates the mechanism's motion,

satisfying the requirements of your servo motors profiles and any

joint, cam-follower, slot-follower, or gear-pair connections, and

records position data for the mechanism's various components It does not take force and mass into account in doing the analysis Therefore, you do not have to specify mass properties for your mechanism

Dynamic entities in the model, such as springs, dampers, gravity, forces/torques, and force motors, do not affect a repeated assembly analysis

• positions of components over time

• interference between components

• trace curves of the mechanism's motion

Force Motors

You use force motors to impose a particular load on a mechanism You can create force motors for your mechanism if you have a Mechanism Dynamics Option license Force motors cause a specific type of load to occur between two bodies in a single degree of freedom You add force motors to your model to prepare it for a dynamic analysis

Force motors cause motion by applying a force on a translational or rotational joint axis

You can place force motors on joint axes You can define as many force motors on a model as you like You can turn force motors on and off within the definition of each dynamic analysis

Download the Component Parts for Assembly

In a system window, create a new directory and download the zip file

exercise_machine.zip

Unzip the file, and set the working directory

Create A New Subassembly Called raiser_subasm.asm The raiser_subasm.asm is consisted of raiser.prt and

raiser_shaft.prt

Click on

Enter the name raiser_subasm

OK

Open raiser.prt, and assemble it at

default location – click

OK

Open raiser_shaft.prt, and click

on Connect tab

Create Pin type connection as the following:

Axis alignment: Axis of the

raiser_shaft ( A_2) is aligned with the axis (A_3) of the hole on

the raiser

For Translation constraint, pick

FRONT datum plane of the

raiser_shaft, and then pick

FRONT datum plane of the

raiser

OK

Save the raiser_subasm.asm

Create A New Subassembly Called pedal_left_subasm.asm

The pedal_left_subasm.asm is consisted of pedal_left.prt and

roller.prt

Click on

Enter the name

pedal_left_subasm

OK

Open pedal_left.prt, and assemble it at

default location – click

OK

Open roller.prt, and click on

cylinder cut) on the pedal_left

For Translation constraint, pick

FRONT datum plane of the roller, and then pick FRONT datum

plane of the pedal_left

OK Save the

pedal_left_subasm.asm

Create A New Subassembly Called pedal_right_subasm.asm

The pedal_right_subasm.asm is consisted of pedal_right.prt and

Open pedal_right.prt, and assemble it

at default location – click

OK

Open roller.prt, and click on

cylinder cut) on the pedal_right

For Translation constraint, pick

FRONT datum plane of the roller, and then pick FRONT datum

plane of the pedal_right

OK

Save the

pedal_right_subasm.asm

Create A New Assembly Called exercise_machine.asm

The complete Mechanism Design Model of exercise machine will be created in this step The total assembly will be consisted of

components and subassemblies created in the previous steps

Click on

Enter the name

exercise_machine

OK

Open chasis.prt, and and

assemble it at default location – click

OK

Create a Slider Connection Between raiser_subasm and chasis

Open raiser_subasm by selecting

Select the Connect tab

Choose Slider type connection

Align axis A_4 of raiser.prt with

A_4 axis of chasis.prt

For Rotation constraint, select back surface of the block of the

raiser.prt, then select the back

inside surface of the vertical

column of the chasis.prt – see

figure below

OK

Note that the raiser_subasm

should slide inside the hollow front column of the chasis

Create Connections Between ramp and raiser_subasm

Left and right ramps should be assembled in this step Each ramp will have two connections which are pin and slider connections

Open ramp.prt by selecting

Select the Connect tab

Choose pin type connection

Align axis A_1 of ramp.prt with

A_2 axis of chasis.prt

For Rotation constraint, select

front surface of the ramp.prt,

then select the front surface of the

chasis pin

OK

To add another connection, click on

Choose slider type connection

Align axis A_3 of ramp.prt with

A_3 axis of raiser_shaft.prt

For Rotation constraint, select

bottom surface of the ramp.prt,

then select the TOP datum plane

of the raiser_shaft

OK

Repeat the same technique to assemble the right ramp with the same type of connection

Create a Pin Connection Between fly_wheel and

Axis alignment: A_2 axis of the

fly_wheel is aligned with the

axis A_1 of the right support of

the chasis – see figure

For Translation constraint, pick

Create Connections Between pedal_left_subasm & Left ramp and pedal_right_subasm & Right ramp

Two connections are needed – pin and slider connection

Open pedal_left_subasm.asm by selecting

Select the Connect tab

Choose pin type connection

Align axis A_1 of pedal_left.prt

with A_4 axis of fly_wheel.prt

For Rotation constraint, select front surface of the

pedal_left.prt, then select the

front surface of the pin of

fly_wheel.prt

OK

To add another connection, click on

Choose slider type connection

Align axis A_2 of roller.prt with

A_2 axis of ramp.prt

For Rotation constraint, select

TOP datum plane of the

roller.prt, then select the top

surface of the ramp

OK

Repeat the same procedure for the right pedal

Open pedal_right_subasm.asm by selecting

Select the Connect tab

Choose pin type connection

Align axis A_1 of pedal_right.prt

with A_5 axis of fly_wheel.prt

For Rotation constraint, select back surface of the

pedal_right.prt, then select the

pin end surface of the

fly_wheel.prt

OK

To add another connection, click on

Choose slider type connection

Align axis A_2 of roller.prt with

A_2 axis of ramp.prt

For Rotation constraint, select

TOP datum plane of the

roller.prt, then select the top

surface of the ramp

OK

Assemble cover.prt to Rear Part of the Machine

Open cover.prt, and assemble it to the machine as shown in the

figure below

Mate the bottom surface of the cover with the top surface of the bottom part of the chasis – see figure below

Align the right surface of the cover with the right surface of the bottom part of the chasis – see figure

Align the front surface of the

Transfer the assembly model to Mechanism

Applications -> Mechanism

Test the Connections

This model has been fully assembled as a MDX (Mechanism Design Extension) model with the appropriate connections To test these connections select

Mechanism -> Connect

Click on Yes Note: If Yes is selected, the bodies in the model will be repositioned such that the assembly

connections have been aligned according to their definition and constraint references If No is

selected, the bodies in the model are returned to their original position

Select from the toolbar The drag dialog box appears

The mechanism has two degree of freedom, the motion created by dragging one

component may be erratic

For this model type it would be prudent to lock one body while

moving the rest In this instance we will lock raiser.prt so we can

independently observe the motion of the other components of the assembly without moving the aforementioned part

Select the Constraints tab in the

Drag dialog box

Select the Body-Body Lock Constraint icons

Select chasis.prt

as a reference part for locked body and then select

raiser.prt as

selected parts to lock to reference

Now that raiser.prt has been

locked, select the Point Drag icon

in the Drag dialogue box

Using the left mouse button, select somewhere on

fly_wheel.prt and drag the

If the middle mouse button is selected the drag operation will be cancelled and the components will return to their original positions

Select Close from the Drag

dialogue box to finish with this step

Closing this dialogue box will automatically cancel the body locks and free up all the bodies to move according to their

connection definitions

Apply the Servo Motors

At this stage, this model has been assembled successfully and the motion of the components has been checked by dynamically

dragging the components Next, servo motors will be applied to certain connections in the model and a Repeated Assembly

analysis will be run to further demonstrate the motion of this model and allow for interference checking during playback of the motion

From Mechanism toolbar, select Define Servo Motors icon

The Servo Motors dialogue box appears

Select New button to create a new driver

Pick the slider joint for raiser.prt

as the Driven Entity Joint Axis

Under Magnitude, select

Cosine

This will display a function and create input fields to assign constants to each of the coefficients in this function

Enter 4.5 for A , 4.5 for C , 10.0

for T (period) and leave the other coefficients at their defaults

Under Graph, select

to plot the motion

of the slider with respect

to time

Note:

Magnitude Settings

Depending on the type of motion you want to impose on your

mechanism, you can define the magnitude of your servo motors or

force motors in many ways The following table lists different types of

functions that Mechanism Design uses to generate the magnitude You

need to enter the values of the coefficients for the functions The value

of x in the function expressions is supplied by the simulation time or,

for force motors, by either the simulation time or a measure you

select

Function

Constant Use if you want a

where

A = Constant

time where

A = Constant

B = Slope Cosine Use if you want to assign

a cosine wave value to the motor profile

q = A*cos(360*x/T + B) + C

Acceleration is chosen

This profile is not applicable for force motors

Cycloidal Use to simulate a cam

profile output q = L*x/T – L*sin (2*Pi*x/T)/2*Pi

where

L = Total rise

T = Period Parabolic Can be used to simulate

a trajectory for a motor q = A*x + 1/2 B(x

2) where

B = Linear term coefficient

C = Quadratic term coefficient

D = Cubic term coefficient Table Use to generate the

magnitude with values from a two-column table

If you have output measure results to a table, you can use that table here

User

Defined Use to specify any kind of complex profile defined

by multiple expression segments

Custom

Load This option is only available for the force

motor definition Use it to apply a complex,

externally-defined set of loads to your model

Use a single profile if possible But you can use a combination of

profiles to generate certain types of motion For example, a

combination of ramp and cosine generates a sinusoidal motion that ramps up over time For more information, see figure shown below which shows different types of motion the motor creates

Example: Types of Motor Profiles

The following graph depicts different types of motion the motor

creates

Following are the values from the formulas that were used to generate the profiles in this graphic:

Select OK to complete the servo motor definition

The Servo Motor icon is created

on the slider joint

The zero position for the joint should be defined

Select Mechanism ->Joint Axis Settings

Then select the slider connection of the raiser and check the

Specify References box

For the Green Body Reference select the top surface of the base

From Mechanism toolbar, select Define Servo Motors icon

The Servo Motors dialogue box appears

Select New button to create a new driver

Select the pin joint for fly_wheel.prt as the driven entity – see

figure below

Then select the Profile tab to define the driving function

In the Profile tab set the specification to Velocity Leave the Initial Angle setting as

Current

This setting would allow you to adjust the initial position of the component with respect to the zero reference prior to the driver starting The driver being

created only needs to spin the

fly_wheel.prt and therefore the

initial position is of no importance

Fill out the Profile tab by entering

a Constant angular velocity A of