ME 301 Final Project

1
ME 301 Final Project

• Scissor Lift Analysis
• Chris Knaack

2
One Degree of Freedom

• One Input- Length of Hydraulic Actuator
• One Output- Height of
• Load

3
Kinematic Diagram

• Small Change in Length of Hydraulic
• Gives Large Change in Height of Deck
• Hydraulics Offer Large Force and Small Range

4
Geometric Symmetry

• Two Scissor Links can be of as diagonals of a
  rectangle
• Thus the angle of Link 1 is the same as Link2
  (Demonstration)
• Lifting Deck always remains Level !!

5
Double Vertical
6
Double Horizontal
7
Forcing Function D(t)

• User selected time domain
• Linear change through Full Range of Motion
• Constant Velocity
• Zero Acceleration

8
Theta(t) Phi(t)

• Theta(t) is Blue
• Phi(t) is Green
• 0 lt Theta lt90
• 0 lt Phi lt 90
• Non-Linear

9
Table Height(t)

• 0 lt TH(t) lt 2m
• Change starts very rapidly
• Change decrease as Table Lifts

10
Path of Linking Point

• Follows Ellipse Path
• Minor Axis is Min D
• Major Axis is Max D

11
Angular Velocities

• Relatively small in working Range
• Explodes to infinity at joint limits

12
Angular Accelerations

• Relatively small in working Range
• Explodes to infinity at joint limits

13
Acceleration of Point C

• Relatively small in working Range
• Explodes to infinity at joint limits

14
Required Actuator Forces

• Must supply this Force to maintain D(t)
• Explodes at Limits
• Roughly 4-6 X Load in Real Range
• Green is Load

15
Shaking Forces

• BLUE is Load
• FN1x is almost zero
• FN1y Fn2y explode at upper limit
• Positive is Crushing
• Negative is Pulling Anchor

16
Internal Joint Forces at Point C

• Infinite at Limits
• Constant is LOAD
• Y in RED
• X in Blue

17
Conclusions

• Joint Limits Prevent Exploding Values at
  Overlapping links (Theta 0 or 90).
• Forces needed is about 5 X Load and fairly
  constant.
• Placement of Load on Table effects dynamics
  drastically.

18
Internal Joint Forces at D E

• Constant Line is Load
• Again Forces Explode at Upper Joint Limit
• Point E in RED
• Point D in Blue
• Both Strictly Vertical
• FD goes negative when D under Load Point