Harmonic drive llc robotics symposium presentation-designing from the inside out; defining robot performance requirements

Defining robot performance requirements and learning how
customized solutions can be the key to success.
Designing From the Inside-Out
Doug Olson
President / CEO
Harmonic Drive LLC
Copyright 2018 Harmonic Drive LLC - All Rights Reserved
1

Empower Your Robot!®
Agenda
• Brief Company Overview
• Product Line Overview
• Technology Overview
• Your Design Requirements
• Mechanical Modifications & Implications
• Performance Customizations
2

Harmonic Drive Systems
(Japan)
Company Overview
Harmonic Drive LLC
(Peabody, MA)
Harmonic Drive AG
(Germany)
3

Component Sets ActuatorsGear Units & Gearheads
Product Line Overview
4

Harmonic Drive® Gear Characteristics
• Zero Backlash
• High Reduction Ratio
• In-line Configuration
• 30:1 To 160:1 Reduction In A Single Stage
• Gear Ratios Determined By Number Of Gear Teeth
• Weight And Size Are Independent Of Gear Ratio
Technology Overview
5

Circular Spline
Wave Generator
Flexspline
Harmonic Drive® Component Set
The Gear is Comprised of Just Three Basic Components
Harmonic Drive® Component Set
6
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Your Design Requirements
Physical Constraints
• Dimensional
• Weight
• Inertia
Environmental
• Operating Temperature
• Vacuum
• Corrosion Resistance
• IP Rating
• Radiation
Life Requirements
• Duty Cycle
• MTBF
• Emergency Stops
Performance Requirements
• Torque / Speed
• Accuracy
• Repeatability
• Dynamic Response
• Velocity Ripple
7

One Size Doesn’t Fit All
• > 70% Of The Products We Produce Are “Specials”
– Therefore, Specials Are Standard
• Our Discussion Today is About Component Sets, but
the Principles Are Common To All Product Lines
– Mechanical Modifications
– Performance Customization
8

Mechanical Modifications
9

Modification Difficulty Cost Tradeoff
CS Hole Pattern Easy Minimal
Fixtures needed if test
data is required
CS Outside Diameter Difficult Production Tooling
Fixtures needed if test data
is required
CS Weight reduction Easy Moderate
Excessive weight reduction
will lower torsional stiffness
CS Material Change
(Stainless Steel)
Easy Moderate None
Circular Spline Modifications
BCD ø
BH ø
• Torque transmission must be evaluated if
smaller or fewer screws are used.
10

OD ø
data is required
data is required
CS Material Change
(Stainless Steel)
Easy Moderate None
• Rabbet or OD can be used to pilot the CS.
• The rabbet can be eliminated.
Rabbet ø
11

data is required
data is required
CS Material Change
(Stainless Steel)
Easy Moderate None
• Typical Weight Reduction
• T cross section
• Pocketing of CS
12

data is required
data is required
CS Material Change
(Stainless Steel)
Easy Moderate None
• Typical Weight Reduction
• T cross section
• Pocketing of CS
• Standard Material – Ductile Iron
• Options
• Low temp chrome plating
• 17-4PH, 15-5PH
13

Flexspline Modifications
BCD ø
BH ø
Pilot ø
FS Hole Pattern Easy Minimal
data is required
FS Pilot Diameter Easy Minimal
data is required
FS Material Change
(Stainless Steel)
Moderate More Significant
Possible reduction in life
depending on load
conditions
• This is the weakest connection point
• If modifying, verify torque transmitting
capacity
• Consider use of Dowel Pins
14

Flexspline Modifications
FS Hole Pattern Easy Minimal
data is required
FS Pilot Diameter Easy Minimal
data is required
FS Material Change
(Stainless Steel)
Moderate More Significant
Possible reduction torque
specifications
• Standard Material: 4340
• Options: 15-5PH, 17-4PH
15

Wave Generator Modifications
WG Bore ø
WG Bore change
(w/ Oldham coupling)
Easy Minimal
data is required
WG Bore Change
(Solid wave generator)
Easy Production Tooling
data is required
WG Material Change
(Stainless Steel)
Easy Moderate None
WG Weight / Inertia
Reduction
Moderate Moderate
Excessive weight
reduction will lower
torsional stiffness
Stainless Steel Wave
Generator Bearing
Easy Significant
Long lead time
Reduced bearing life
Bearing Separator
Material Change (Brass,
Phenolic…)
Moderate
Moderate to
significant
depending on
quantity
Lead time
• Semi-standard sizes are readily available
• Custom sizes available up to max
diameter limit
16

WG Bore change
Easy Minimal
data is required
WG Bore Change
data is required
WG Material Change
(Stainless Steel)
Easy Moderate None
WG Weight / Inertia
Reduction
Moderate Moderate
Excessive weight
torsional stiffness
Generator Bearing
Easy Significant
Long lead time
Bearing Separator
Material Change (Brass,
Phenolic…)
Moderate
Moderate to
significant
depending on
quantity
Lead time
• Standard Material: Steel
• Options: 15-5PH, 17-4PH
17

WG Bore change
Easy Minimal
data is required
WG Bore Change
data is required
WG Material Change
(Stainless Steel)
Easy Moderate None
WG Weight (Inertia)
Reduction
Moderate Moderate
Excessive weight
torsional stiffness
Generator Bearing
Easy Significant
Long lead time
Bearing Separator
Material Change
(Brass, Phenolic…)
Moderate
Moderate to
significant
depending on
quantity
Lead time
• Wave Generator weight reduction is highly
effective in improving the dynamic
response of the system. Precision in
assembly is required if no Oldham
18

WG Bore change
Easy Minimal
data is required
WG Bore Change
data is required
WG Material Change
(Stainless Steel)
Easy Moderate None
WG Weight / Inertia
Reduction
Moderate Moderate
Excessive weight
torsional stiffness
Generator Bearing
Easy Significant
Long lead time
Bearing Separator
Material Change
(Brass, Phenolic…)
Moderate
Moderate to
significant
depending on
quantity
Lead time
• Wave Generator weight reduction is highly
effective in improving the dynamic
response of the system. Precision in
assembly is required if no Oldham
• 440C Bearings are typically only used for
space flight applications
• Environmental conditions sometimes
requires bearing separator material
changes (temperature extremes, vacuum,
radiation)
19

Mechanical Modifications
20

Performance Customization
Accuracy
Torsional Stiffness
Starting Torque
Back-driving Torque
21

• Repeatability is defined as ± ½
the maximum difference in
position when returning to the
same point multiple times from
the same direction.
(Single Direction Repeatability)
Accuracy vs Repeatability
• Accuracy is defined as the
difference between the
commanded position and
the actual position of the
gear.
• 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 =
∅𝑖𝑖 𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖
𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
− ∅𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
• We measure the accuracy of
the gear throughout one full
revolution of the output and
define that as
transmission error
22

Positional Accuracy
High Accuracy Relatively easy Minimal None
Increased Torsional
Stiffness
Relatively easy Minimal Increased starting torque
Low Starting Torque Relatively easy Minimal
Lower torsional stiffness
(depending on
requirement)
Low Back-driving
Torque
Relatively easy Minimal
(depending on
requirement)
• Typical Accuracy* <1 arc-min
• Improved Accuracy < 30 arc-sec
• High Accuracy specification is beneficial for:
• Precise positioning applications
• When low velocity ripple is required
• Velocity Ripple ~ d/dt (Position Error)
• When vibration is of critical concern
• Vibration ~ d2/dt2 (Position Error)
• Test data can be provided
• Repeatability is typically ± 5 arc-sec
27.72 arc-sec
1 Wave Generator
Revolution = 2 Cycles
* Size 20 and larger
23

Torsional Stiffness
Increased Torsional
Stiffness
(depending on
requirement)
Low Back-driving
Torque
(depending on
requirement)
• Torsional Stiffness of Harmonic Gearing is
non-linear
• Broken into three regions K1, K2, K3
• Catalog values are typical and not
guaranteed minimums.
• High stiffness specification is beneficial for
• Precise positioning applications where
load conditions may vary (minimize
deflection)
• Vibration reduction due to increase in
resonant frequency of the system
• Values are verified with test data providedK1 Stiffness is the region where the greatest
increase is achieved
24

Starting & Back-driving Torque
Increased Torsional
Stiffness
(depending on
requirement)
Low Back-driving
Torque
(depending on
requirement)
• Low starting torque beneficial to minimize
dead band when in current mode
• Low Back-driving torque is beneficial when
the robot arm need to be manually
positioned by a user – such as for a cobot
or surgical robot
• The size of gear, reduction ratio as well as
the type and amount of lubricant will also
have a large influence
• Both of these characteristics are inter-
dependent with torsional stiffness
• Typically with careful selection of the gear
type, size & gear tooth profile, all
requirements can be met
• In applications where back-driving is not permissible, a brake or other
failsafe device must be used. In no circumstance should the gear set’s
published Back Driving Torque value be relied upon to prevent
movement of the assembly
25

Custom Actuators & Gear Units
• Custom actuators and gear units are also available
• Minor modifications to completely custom designs
26

In Closing
• Conceptual and Preliminary design reviews are
invaluable to identify opportunities for improvements
to assure a successful implementation.
• We are always available to
provide design & engineering
support –free of charge.
• Our Goal is Your Success
27

Learn More About the Inventor!
https://www.youtube.com/watch?v=1sQK1dmzT04&feature=youtu.be http://www.waltmusser.org
28

Doug Olson
Harmonic Drive LLC
DOlson@HarmonicDrive.net
Questions?
Chris Simo
Electromate (Toronto)
Chris@Electromate.com
(905) 850-7447
Rich Kawko
Harmonic Drive LLC
Rkawko@HarmonicDrive.net
(978) 573-3482
Stamati Georgaris
Electromate (Montreal)
Stamati@Electromate.com
(905) 850-7447
29

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