introduction to lifts and manipulators

7/28/2019 Introduction to Lifts and Manipulators

http://slidepdf.com/reader/full/introduction-to-lifts-and-manipulators 1/24



Lifts

Four Bar Mechanisms

Rotary Jointed Arms

Scissor Lifts

Telescoping Lifts

Combined Systems

Lift Concepts



Overview

Unique: no straight support; but rather linked and folding supportsstretch platform upwards

Powered by hydraulics or motors; bumpy ride

Doesn’t travel at constant velocity; faster during middle ofjourney/slower with more extension

Pros

Max height of platform is adjustable

Height determined by # and length of linkages

Great for straight lifts

Cons Requires huge force to start the lift

Synchronizing two scissors is difficult

Complex design

Scissor Lifts Lifts



Overview

Basic principle of human arm: shoulder, elbow, wrist

Different types of manipulators (i.e. gripper) can be attached

Pros

3 axes of motion: pitch, yaw, roll

Can emulate human arm

Useful when gripping objects is objective

Cons

Failure of joint caused by pressure at shoulder and base plate Each joint requires a motor; operated independently

Thus, programming is tricky

Rotary Jointed Arms Lifts



Overview

Simple and effective

Opposite bars remain parallel, retaining orientation of object

Pros

Simple, effective

Object retains orientation Only one joint to motorize

Easily programmed

Provides reach

Cons Joint may endure heavy pressure

Required to lift “outside of the box”

Vulnerable to side hits

4 Bar Mechanisms Lifts



Overview

Commonly used within forklifts and cranes

Extend in one direction

Powered by chain or piston

Also referred to as extension lifts

Pros

Extends “within the box”; mechanism protected by base

Operates on a relatively uncomplicated system

Requires only one power sourceCons

Multiple segments translate up; higher center of gravity

Can become complex

Telescoping Lifts Lifts



Overview

Combining systems can help when one doesn’t cut it

Pros

Combines the pros from the various lift mechanisms used

Cons

Can quickly become too complex

Combined Systems Lifts



Strategy

What is being manipulated?

Types of Intake

Continuous

Single

StorageAcquisition Zone

Placements / Alignments / Accuracy

Grip of Object

How much friction is needed?Motors and Servos

Limits

Gear Ratios

Manipulators Manipulators



1. Find out about the game

2. Make requirements

3. Determine drive train

4. Determine best lift mechanism

5. Determine best manipulator

If robot doesn’t drive efficiently, arm and manipulator will beuseless.

K.I.S.S.

Strategy Manipulators



Ball

Continuous and single object grabbers are useful

Types of Manipulators

2 tank treads horizontally / vertically aligned 3 / 4 prong grabber

2 point grabber / fork

Bucket intake

Roller

Use soft grip to effectively control and contain the ball

What Is Being Manipulated? Manipulators



What Is Being Manipulated?

Ring



2 tank treads horizontally / vertically aligned 3 / 4 prong grabber

2 point grabber / fork

Bucket intake

Roller

Use soft grip to effectively control and contain the ring

Manipulators




Square



3 / 4 prong grabber with grip

2 point grabber

Use strong grip to effectively control and contain the square

Manipulators




Triangles

Single object grabbers are useful


3 / 4 point grabber

Flat bottom and X shaped intake roller

Use strong grip to effectively control and contain the triangle

Manipulators



All items of same size can be similarly stored

Stack

Tank treads

Divide

Dump tank (basket)

Simply grab and drop to goal

Storage of Objects Manipulators



Must be decided with base so arm and

manipulator can be stored when

Trying to fit the size

Effectively obtain objects

U-shaped base

360˚ pivot joint (& arm extender) Manipulator attached to base

Storage of Arm & Manipulator Manipulators



Intake area of the object

Large intake area is optimal

During match, easiest and fastest for driver(s)

Get multiple objects at once

Keep in mind type of object that will bemanipulated

Acquisition Size Manipulators



Scoring object on/into goal must be accurate

and easy

Optimal stability and accuracy during scoring

Alignment: know how mechanism works and

where it needs to be positioned

Drivers should easily be able to work with

placement; manipulator should be accurate

Placements, Alignments, Accuracy Manipulators



Why is grip important?

Manipulator has to efficiently contain the object

How do you obtain grip?

Friction

Grip of Object & Friction Needed Manipulators

M d S



Enable arms and manipulators to move

Motors

Can turn a shaft CW and CCW as many degrees as

desired

Used for continuous intake

Servos

Can turn a shift CW and CCW, but only 180˚

in eachdirection

Used for <360˚ pivot joints

Motors and Servos Manipulators

Li i



Types of Stops/Limits

Hard stop Sturdy metal part of robot

Physically doesn’t allow arm / manipulator to go any

further May burn a clutch / break motor

Soft stop Limit switches

Limits should be placed anywhere where there is ahard stop

Limits Manipulators

G R i



Gear the ratio down Working against a lot of weight

1:2 – one shaft revolution = two motor revolutions

Gear the ratio up Working with less weight and quicker speed

2:1 – two shaft revolutions = one motor revolution

Must have enough torque to pull arm and manipulator

up and down Must have enough torque to contain object that’s being

manipulated

Gear Ratios Manipulators

THANK YOU!



Beach Cities Robotics

Northrop Grumman

OCRLC

Orange Coast College

FIRST

VEX, IFI, VRC

THANK YOU!

CHALLENGE!



CHALLENGE!

24 ft. 3 in.

Object: Ping Pong BallGoal: Obelisk

Objective:

Score ping pong balls into obelisk

Challenge:Design an arm and manipulator

for this task.

d: 2 in.

introduction to lifts and manipulators

Documents