- 微博 QQ QQ空间 贴吧
BASIC MACHINES = intro-Lever-screw -wedge-MA
1 . Topics to discuss today • Simple machines • Compound machines • Lever • Linkage • Wedge • Mechanical Advantage • Inclined plane • Screw
2 . To do in class • Mechanical design is an important component of this class – how it relates to your project • What you want to learn? • What you plan to do?
3 .• This material is easy and part of it you can read by yourself. • When you read it, please think how you can apply these ideas in practical robots. • Look also to internet to find who sells these and similar items that can be used in your robot
4 . Conclusion on projects • Mechanical design is an important component of this class • This class is not only programming, you have to pay more attention to mechanical and interfacing aspects of robot design. • Robot programming is different from standard programming, it is a real time application programming.
6 .Stages of robot design
7 . Levels of robot creation Robot System Integration Robot Application Programming Robot Teaching Robot Language Robot System Architecture MOTORS and ACTUATORS Sensor and Vision Internet Mechanical Robot Design • A class as a whole covers all of the above • Your project(s) should cover few of these
8 .Homework: Kinematic Model of the robot
11 . Part of your Homework • Create a model, as in the previous two slides, for your robot • Write all necessary data for torques, angles and length of arms etc.
12 . Kinematics • The study of motion without regard to the forces or mass of the things moving. • Kinematic diagrams are scaled drawings symbolizing how mechanisms work. • We study robot kinematics in Fall • We study dynamics in Winter
13 . 1. Gears 2. Pulleys 3. Chains 4. Cams 5. Bearings 6. Wheel and Axle Examples of 7. Inclined Plane machines 8. Wedge 9. Screw 10. Lever 11. Cranks and sliders 12. Ratcheting mechanisms 13. Clutches 14. Brakes
14 . Machines and Tools 1. Machines and tools are mechanical devices that work by transmitting or converting energy. 2. Machines are made up of a variety of mechanisms. 3. What are some examples of machines?
15 . Simple Machines Screw Inclined Plane Wedge Pulley Wheel and Axle Lever All of these are related to robotics. Think how?
16 . Mechanisms 1. Mechanisms help extend human capability by creating some desired output or motion. 2. A mechanism takes an input motion or force and creates a desired output motion or force. Motion MECHANISM Motion or force or force
17 . Types of Motion • Common types of motion: – Linear – Reciprocal – Rotary – Oscillating All these have applications in robotics
18 . Definitions: Energy: Ability to do work Work = Force * Distance Force: A Push or a Pull
20 . Rotating Arms Torques in arm design are large gear bolted to arm Use counterweights and gears to compensate cou n we ter igh Attach the gear to the arm motor t Attach the motor to the robot driven gear
21 . Role of Linkages • Linkages transmit the motion or force to the desired output location. • Linkages: 1. change the direction of the force 2. Change the length of motion of the force 3. Split the motion and force over multiple paths
23 . Lever – Downward motion at one end results in upward motion at the other end. – Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the Pivot point, fulcrum force is applied http://www.csmate.colostate.edu/cltw/cohortpages/viney/balance.html
24 . Explanation Simple Lever Machine • This simple machine is based on the position of the effort force, resistance force, and fulcrum. • First class lever – Fulcrum located between effort force and resistance force – Usually used to multiply a force This kind of lever – Example: Example Seesaw changes the direction of force. R Resistance force E Effort F length1 force length2 R * length1 = E * lenght2
25 . Engagement Simple Experiment: Balancing Act • Using only a meter stick and a wooden block, balance two masses in a seesaw kind of structure. Do this by • How did you get them to balance? yourself, not in – Could you do it in one try? class • Compare your setup with other possible setups This is useful in robot arm design
26 . Exploration Simple Experiment: Balancing Act Lever Forces • Materials – Computer/calculator – Force Probe – 500g mass – String We do such projects in – Meter stick High school robotics – Wooden Block Do not discuss next 2 slides in class
27 . Exploration Lever Forces Simple Experiment: Balancing Act • Measure the Weight of the 500g mass (in Newtons). • Balance the middle of the meter stick on the wooden block. • Place the 500g mass at the 90 cm line. • Attach the string to the meter stick at the 10 cm line. • Attach the string to the force meter and pull down on the sensor until the meter stick is balanced. • Record the force needed to balance the meter stick. • Repeat the above steps with the 500g mass at the 70 cm line and the 60 cm line.
28 . Exploration Simple Experiment: Balancing Act Lever Forces • After recording your data in a table, perform the following calculations for the three trials: – Divide the weight of the 500g mass by the force required to balance the meter stick. – Divide the distance between the force meter and the wooden block by the distance between the 500g mass and the wooden block. • How do these numbers compare? • What do these numbers indicate about the lever system?
29 . Explanation Why use a Simple Machine? • Simple Machines make work easier by giving the user a mechanical advantage. • How do we calculate the mechanical advantage for a lever system? • Ideal Mechanical Advantage (IMA) = L effort / Lresistance Leffort is the distance between the effort force and the fulcrum Lresistance is the distance between the resistance force and the fulcrum • Why do we stipulate that the MA is ideal? Because we’ve assumed that the machine puts out exactly as much work as we put in. This implies 100% efficiency • This situation is never possible…why? Mechanical Advantage = MA 100% efficiency is never possible because of FRICTION.