commercialization of robotic prototypes: improving the concept for manufacturability and sale

Commercialization of Robotic Prototypes:

Improving the Concept for

Manufacturability and SaleJon Appleby

Engineering Manager, Boston

Acorn Product Development

Commercialization of Robotic Prototypes:

“The big problem is production. They overestimate how easy it is to do. It’s really hard.”

- Dimitry Grishin, xconomy 9/24/14

Late 2010

3 Employees

3 Robots

Mid 2012

70 Employees

100+ Robots

Improving on the Concept: Our Case Study

Improving on the Concept: Who we are

• Goals and requirements

• Breadboard development, component

selection

• Packaging options

• Drive-Train analysis

• Thermal modeling

• Structure – materials, process capability,

tooling approach?

• Manufacturing plan

• Cost analysis

• Down-selection of concepts, layouts,

performance metrics.

Improving on the Concept: How to Get There

• CAD design

• Updated analysis, thermal,

structural, tolerance

• Mfg Qualification, sourcing

plan.

• DFM integration from supply

base.

• Prototype build



selection





tooling approach?


• Cost analysis




• CAD design

• Updated analysis, thermal,

structural, tolerance

• Mfg Qualification, sourcing

plan.

• DFM integration from supply

base.

• Prototype build

• “Test” – Validate, don’t test.

• Production design, analysis

updates.

• Vendor management

• Tool reviews, mold-flow, First-

Article inspection

• Qualification

• CM build support



selection





tooling approach?


• Cost analysis




The Prototype

Phase 1: Concept Generation, Evaluation

• Defining Realistic Goals/Objectives for the Commercial Product

• Designing for Manufacturing & Challenges

• Weight

• Strength

• Performance

Phase 2: Detailed Design

• CAD Implementations

• Analysis refinements

Phase 3: Test, Production Design

• Supply Chain Challenges

• Testing, Reliability

The Results

Improving on the Concept: A Case Study

The starting point:Machined aluminum

chassis. CNC,

expensive, heavy.

Compression, flat gasket

sealing

Bolt-in-place, all at once

assembly process.

Functional! Runs great, performs all basic tasks.

Too expensive, too heavy

Not a product, yet.

COTS / Commercial drive

components.

Poor reliability, hand-wired

Over-stressed components

The Prototype

• Weight targets –

• Prototype was 35+ lbs.

• Target = <25lbs. This includes “fixed” weight metrics like battery, motor, electronics.

• Rugged

• Needs to be run by un-trained operators on unknown terrain.

• Durable, pull it out, use, put it back.

• 60” repeated drop test requirement, thrown deployment

• Custom treads

• Modular payloads

• Need space, lots of it! Future expansion possibilities

• Common interface, power, high-speed signal, water-proof

• Costs

• Needed a reduction of ~>50% in BOM (Bill of Material) costs

• This is a must for the business case

Phase 1: Goals, Realistic and Otherwise

At the concept level:

How do we fit all the required components, and meet the

performance requirements?

Evaluated several different layouts, each with:

• Thermal solutions – solar load, internal power

dissipation

• Payload capability – how big, how many?

• Climbing performance - FWD, RWD, CG, traction,

balance

• Cost

Phase 1: Concept Generation

How to we design around the CNC chassis, what are the alternatives?

Plastics: Low cost

High complexity, feature rich

Good impact, low strength

Major risks to structural & tolerance goals

New supply chain

Thixomolding: Licensed magnesium die-cast process

~Low cost, high complexity

High strength, light weight.

More accurate than aluminum die casting

New supply chain

These choices impact our concept – we need analysis at the system level.

Gaining in popularity, camera shells,

transmission cases, consumer products.

Phase 1: Concept Generation - Materials

• Will this survive the ambient conditions?

>45C ambient, desert solar load

Multiple levels & Increasing effort and reward:

• Hand-Calcs – quick, can rapidly apply to several

concepts. Rinse, Repeat as concepts evolve.

• CFD – for times when you need better than ~+/-

25% accuracy. This are slow, time-consuming,

and not 100% accurate either.

Phase 1: Concept Generation – Thermal Evaluation

We were very concerned on the drop impact:

• High cantilevered loads

• Can we use SST for the shafts, aluminum, Ti?

• Relationship between shaft OD and attachment

method?

• Will our plastic construction concepts be strong

enough?

g

Phase 1: Concept Generation – Structural Evaluation

Took several concept iterations to support the cold

temperature drop performance.

Goals

+

Brainstorming

+

Layout Options

+

Material Choices

Analysis:

Thermal

Structural

Tolerance

Performance

Down-select,

Refine, Repeat

Phase 1: Concept Generation – Synthesis and Analysis

Centerpiece of the re-design effort was a common, single-molded chassis solution.

Early concept Model

Used for basic strength

calculations, molding

feedback, vendor RFQ

process

Production Design Model

Final FEA simulations

Tolerance analysis

Phase 2: Detailed Design - Chassis

Tolerances are a key aspect of the detailed design.

There are several approaches here, each with their own advantages:

Worst-Case

Analysis:

“RSS”, Root Sum

Squared

Direct Linearization

Method

Monte-Carlo

Setup Time

(fast)

(slow)(high)

Accuracy

(low)

In everyone’s toolbox. Not realistic, doesn’t hold up for

multi-part solutions. Can’t plan for the worst!

Good approximation, weights all variables the same.

Difficult to get a predicative value.

Good balance of speed, accuracy. Combines actual

process capability into a predictive approach.

“Holy Grail”. Iterative, simulation to predict results. This

is only as good as your input data. Not recommended

unless you have measured manufacturing data on your

parts.

Phase 2: Detailed Design – Tolerance Analysis

Direct Linearization Method Approach:

Element 1:

Plastic

Feature

Element 2:

Shaft

Dimension

Element 3:

Bolt fit in

clearance

hole

Sum generates a

composite

Gaussian curve

Adding up

our

elements,

based on a

sketched

loop

New Predicted Gaussian

3 sigma = 99.9%,

or 1350 DPPM

4 sigma =

99.997%, or 32

DPPM


Element n:

Hole clearance,

biased by gravity

Gear Mesh Tolerance

Loop generation, from one side of the

gap to the other.

Expected

Center

distance?

Solving for our predicted distances:

Z (Sigma) = 3.98 @ +/- 0.27mm

Or, 99.997% of the time, we expect

+/- 0.27mm of the CAD distance.


Revisit our thermal solutions, at a systems level.

Early runs shown – safe plastic touch limits exceeded!

Verification of motor peak

temperatures

Phase 2: Detailed Design – Thermal Refinement

Plastics are not an overnight solution.

SLA, 3D print, machined equivalents are good mock-ups, but not functional equivalents.

We decided to build an iterative option, with a sheetmetal core chassis.

This gave us a working platform, with the similar weight profile, in a short amount of time:

Interim path:

Production path:

Phase 2: Detailed Design - Chassis

• 4-slide, large molded chassis in 8

weeks?

• Yes, it can be done!

• Global Sourcing, Vetting

suppliers remotely

• Tooling < $80k investment

• Vendor Management is key

• Tooling approvals, design

approvals, be involved.

• In process photos are a must

• Weekly communication at a

minimum

In process B-plate

In process slide

Phase 3: Supply Chain Challenges

• Tooling Drawing Reviews

• Inserts as needed, materials

• Cooling lines, gating, runner systems, ejection

Typical tool construction

drawings

Typical cooling and runner

visualizations


• Mold-Flow Studies

• Gate & Process

verification

• Venting, Air Trap

concerns

• Done ourselves, and/or

cross-checked from

vendor provided data.


First Article Inspection

• Just because it’s done – doesn’t mean it’s right!


• Drop Test – this was a challenge with a high mass

object…

• Aggressive 5ft drop requirement onto pavement

Phase 3: Testing, Reliability

• Still break a few eggs!

Traced back to material issue

at supplier.

Wrong level of impact modifier

not present in the parts

provided.


Empirical measurements of thermal solutions.

Done @ max power conditions, per CFD models.

CFD modeling assumed max power

@ ½ speed. Testing did not include

airflow over robot. Predicted values

are 20% lower.

Good correlation otherwise (10-20%

resolution)


Lighter, Cheaper, More Capable!

• Weight savings of >10lbs

• Reduction in cost by > than an order of magnitude!

• BOM Cost Start: $10,000’s per system

• BOM Cost End: $100’s per system

• Final part count:

• 3x Die-cast/Thixo

• 25x Injection Molding

• 7x CNC

• 19x Sheetmetal

• 2x Extrusion

• Passed ruggedness/durability tests

• Payload support increase by >100%

The Results:

In Action….

The Results:

• This is hard! Production design requires different tool kits, different

approaches to meet the cost, manufacturability, performance targets.

• Production design doesn’t mean limited functionality!

• The concept – it all starts there.

• Analyze, proceed with confidence, & validate

The Results:

Q and A

Thank You

(Come see the robot in Booth 520!)

Address Contact1 Broadway, 14th Floor Barry Braunstein

Cambridge, MA 02142 P 617-475-1541

E [email protected]

mailto:[email protected]