ME 20N: Haptics: Engineering Touch Autumn 2017

Week 2:Haptic device design and

kinematics

Allison M. OkamuraStanford University

3D printing introductionby Melisa Orta Martinez, Kaitlyn Gee, and Tyler Cloyd

Hapkit introduction

Kinematics describes the motion of points, bodies, or groups of bodies

Kinematic analysis does not require any knowledge about what forces cause the motion

Kinematics is a branch of classical mechanics

Our goal is to find equations that describe the kinematics of a mechanism

Kinematics

In this class, a key kinematic relationship is:

Kinematic Relationships

s = r✓arc length radius angle

(in radians!)

✓r

s

radians = 180 degrees⇡

Belt-on-pulleys example

Kinematic Relationships

✓1 r1

✓2r2

s1 = r1✓1

s2 = r2✓2

x = s1 = s2

x

✓2 =r1r2

✓1

Q: if , which pulley rotates more?

r1 > r2

pulley 1

pulley 2

Hapkit Kinematics: Motions

✓pulley

✓sector

rpulley

rpulley

✓pulley

= rsector

✓sector

x

handle

= r

handle

✓

sector

x

handle

=r

handle

r

pulley

r

sector

✓

pulley

rsector

rhandle

xhandle

Q: The sensor measures . Would you make larger or smaller to more accurately compute ?

x

handle

= r

handle

✓

sector

rpulley

✓pulley

= rsector

✓sector

x

handle

= r

handle

✓

sector

Torque, or moment, is the tendency of a force to rotate an object.

If a force is perpendicular to r (the vector connecting the point about which the torque acts to the point at which the force is applied),

this is the scalar relationship between force and torque:

Force-torque Relationships

torque radius

⌧ = Fr

force

r⌧

F

Q: Why are transmissions (like the cable drive in Hapkit) typically designed so that the force will be perpendicular to r?

Belt-on-pulleys example

Force-Torque Relationships

r1

r2

⌧1

⌧2

F1

F2

⌧1 = F1r1

F1 =⌧1r1

F1 = F2

⌧2 = F2r2

⌧2 =r2r1

⌧1

Hapkit Kinematics: Forces/Torques

rpulley

rsector

rhandle

Fhandle

⌧pulley

⌧sector

⌧pulley

rpulley

=⌧sector

rsector

Fhandle

=⌧sector

rhandle

Fhandle

=rsector

rhandle

rpulley

⌧pulley

⌧ = Frrelationship between

force and torque:

Q: Say the motor can generate a torque . What radius would you change to increase ?

⌧pulley

= ⌧max

Fhandle

=⌧sector

rhandle

Solidworksby Melisa Orta Martinez, Kaitlyn Gee, and Tyler Cloyd

Your TO DO list• If you have not done so already, complete Product Realization

Lab safety training by Thursday (http://webshop.stanford.edu).

• This Thursday, meet at 1:30 pm SHARP outside Room 36 in the Huang Center (this is the PRL Room 36). WEAR CLOSED-FOOT SHOES!

• Personalize and 3D print your Hapkit handle.

• On Tuesday, bring your laptop and power cord to class, along with your printed Hapkit handle.