week 2: haptic device design and kinematics · week 2 slides author: allison okamura created date:...
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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.