Round Baler Weighing SystemCNH Design Team

R. Andrew HackendornChris MeehanDan TraubJohn ElliottPhil Zandona

Project Goal• Determine if a load cell based weighing system is a feasible and marketable design.

• Using the three load cells provided by CNH, develop a kit to modify the round baler so that it may dynamically weigh hay bales. 

• Develop a method for accurately filtering and analyzing data.

Project Benefits

• Real time bale weights– Can determine bale size by 

more than simply diameter

– Can track more productive areas of farm land with GPS

• CNH will have an advantage over competitors by offering a round baler with the option of obtaining a dynamic bale weight

~6 ft

System View

Axle Load Cell

Axle Load CellHitch Load Cell

Inclinometers

SignalConditioner

Filtering/Processing  Algorithm & Display

Free Body Diagram

R2

R1R3

Total Weight = W = R1 + R2 + R3

W

Error Due to Incline

• Load cells read normal to baler/ground

• True weight will not be reflected

• Inclinometers will attempt to compensate for this

Weight of Baler

Load Cell Readings

Error Due to Incline

Angle (degrees)

Error(%)

-Because of error we chose inclinometers in two orthogonal directions-We multiply the reactions by the cosine of the angles read by each inclinometer

Concept Generation

Wants, Metrics, and Target Values

Ranked Top Metrics Rate of Importance

Target Value

Parts Changed on Current Baler 14% < 1Number of Parts of Kit 13% < 15.0Manufacturing Cost 13% < $1300.0

Maintain Existing Dimensions 13%Hitch ‐Within 2” any directionAxle ‐ Only move back (< 6”)

Number of Steps in Assembly 11% < 50

Dynamic Weight Accuracy 7% 5 percentStatic Weight Accuracy 7% 5 percent

Ranked Project Wants 

Easy to Attach Kit 

Accurate Weight 

Modification of Baler 

Time to Fail  Cost  Simplicity  Size 

Rate of Importance 

25% 20% 20% 15% 10% 5% 5%

Hitch Concept• Concept shaped to “hug” existing hitch structure.

• Hitch location is identical to existing design. 

Load Cell

Connection to Tractor

Bolt holes for attachment to hitch ‐1000

0

1000

2000

3000

4000

5000

Hitch 1 Hitch 2 Hitch 3

Concepts vs. Score

Hitch Concept

Hitch Concept ‐ Analysis

• Dynamic load factor of 2 applied (2270 lbs)

• Stress analysis shows FOS of 1.4

Axle Concept

• Load cell would plug into “sleeve” that would be bolted into the existing hole in the orange axle. 

• Simple design – 2 Parts

‐2000

0

2000

4000

6000

Axle 1 Axle 2 Axle 3

Concepts vs. Score

Axle Concept

• The blue arrow indicates the far end of the load cell in the sleeve. 

• Because of the positioning of the load cell, the new axle keeps exact camber angle as the existing axle. 

Load CellSupport Bracket

Axle Concept ‐ Analysis

• Dynamic load factor of 2 applied (5500lbs)

• Stress analysis shows a factor of safety of about 1.5

• Weakest point was located in load cell itself, not in axle structure

Blue is a FOS greater than 1

Installation of Selected Concepts

Hitch Installation

• Removed old hitch attachment and installed our concept.

• Metrics Satisfied – Only 2 parts

– 5 bolts to install 

– Original dimensions unaltered 

Axle InstallationLoad Cell and Sleeve Assembly

Load Cell / Wheel Hub Assembly Complete Assembly

• Metrics Satisfied– 4 parts per wheel

– Half hour installation

– Original dimensions unaltered

Cost AnalysisRaw Material 

($ / lb)Weight (lb)

Assemblies (#)

Total Cost ($)

Axle  1.35 7.2 1 9.72

Hitch 1.35 15.2 1 20.52

Number of Raw Pieces

Time to machine raw pieces (hrs)

Time to assembly raw pieces including welds(hrs)

Cost ($)

Hitch 7 4 1.5 165.00

Axle 4 4 .5 135.00

300.00

*NOTE: 1 Man Hour = $30

Labor

Parts

Cost ($) Quantity (#) Total ($)

Load Cell 130 3 390

Inclinometer 31 2 61

Conditioner 300 1 300

Total: 751

Hardware

Target Value

• $1080.00 standard cost• Standard cost includes material and plant labor to install•Satisfies metric target value (< $1300)

• Retail price of ~$3,240 for factory installed option

Testing and Analysis

System Calibration• Testing load cells with mower at 

the UD Agricultural School (could achieve same PTO speed as baler)

• Confirmed mode of collecting data 

• Preliminary data acquired to gain insight on filtering techniques

• Determined load cell scale factors

• Similar method used for inclinometers

Final Testing PlanAll tests with PTO engaged:

1) Baling 

2) Flat ground* 

3) Bump Track*

4) Changed Roll*

5) Changed Pitch**Full bale in chamber

Sample Results

Right Axle Load Cell

• Data acquired while baling

Roll (left/right) Inclinometer

• Bump Track Raw Data

•At 4o, less than 1%        error induced w/o corrections

Increasing weight

4 degrees

-4 degrees

150 sec

Bal

e W

eigh

t, lb

s

1500

Data Analysis

Frequency, Hz

Am

plitu

de

PTO Freq

Fourier TransformAfter converting from time domain to frequency domain, we observe some of the dominating frequencies contributing to the data noise, such as the PTO.

Error AnalysisFiltering Technique

Flat Ground  and Baling Testing

• We used the Butterworth lowpass filter to remove the high frequency noise

• We found that a 5th order filter with a cut off frequency of 0.00075Hz best fit our data

• BLUE – Raw data

• GREEN – Data after filtering

Flat Ground, Bale in Chamber

Time, s

Bal

e W

eigh

t, lb

s

Baling

Time, s

Bal

e W

eigh

t, lb

s

Data Analysis

Flat Ground  and Baling Testing

• Preliminary analysis utilized running averages and interval averages (after combining all components)

• RED – Raw data

• GREEN – Data after interval avg.

• BLUE – Data after running avg.

Flat Ground, Bale in Chamber

Time, s

Bal

e W

eigh

t, lb

s

Baling

Time, s

Bal

e W

eigh

t, lb

s

Error AnalysisAveraging Technique

5 Second Intervals1 Second Intervals

• Increasing time interval• Made curve smoother and reduced maximum error• Error = 2.83%

• Shorter time interval• Curve still noisy• Error = 7.55%

Error Analysis

Using only averaging techniques the accuracy metric (< 5%) was satisfied

Interval of 3.48 seconds is within 5% errorEach load cell is off by a constant factor, leading to a correction factor of 1.08

Target Interval = 3.5s

Prototype Conclusion

ALL Initial metrics for design have been satisfied!

– With prototyped concept proven feasible, a productionlevel design can be developed

Production Level Design

• Both designs contain minor differences from prototypes

• Elongated load cell is the major difference

Production Hitch Production Axle

Questions?

Concept SelectionUDesign

Benchmarking

• CNH Criteria 

• CNH Grinder / Mixer Machine 

• Two Online Journals – www.elsevier.com 

• Vermeer 605 Super M Cornstalk Special Baler

InclinometersChange in Pitch:

z

xѲ

ground

axle

Ѳ

hitch

Lh

La

h

• Looking at the Baler geometries we are capable of solving for the weight of baler and hay given one force measurement.

Preliminary Hitch Concepts

Concept 1

Concept 2

Concept 3

Preliminary Axle Concepts

Concept 1 Concept 2

Concept 3

Concept Selection

• Using our metrics and target values, we used UDesign to give each of our concepts a score.

• Benchmark score: 1660 

• Winning Hitch score: 4556

• Winning Axle score: 5853

Axle Installation

• Contrary to CNH’s drawings, the bolt hole to attach the spindle was oriented 25o off

– Did not allow for correct load cell orientation

• Needed to install a new axle

º25

Actual Location

Required Location

Original hole location on old axle

Axle Installation

• New axle required modified support bracket

• Installed 2 strips connecting the brackets

• Metrics Satisfied– 4 parts per wheel

– Half hour installation

– Original dimensions unaltered

Original Support BracketNew Support Bracket

Prototype Data Acquisition Overview1. Load Cell‐ Output Rating:  1.0 mV/V = 9382 

lbs‐ Accuracy = 99.75%‐ Max. Excitation Voltage = 20 V 

(AC or DC)‐ Input Resistance = 350 +20/‐0 Ω‐ Output Resistance = 350 Ω

2. Conditioner‐ Model:  Somat 2100‐ Allowable Input Voltage = 7.5–

18 V‐ Use Analog for mV/V 

Calibration

3. Cab Display‐ Laptop‐ USB Powered‐ Filtering and Signal Processing‐ Display Bale Weigh

Project TimelineTasks

1‐Sep 8‐Sep 15‐Sep 22‐Sep 29‐Sep 6‐Oct 13‐Oct 20‐Oct 27‐Oct 3‐Nov 10‐Nov 17‐Nov 24‐Nov 1‐Dec 8‐Dec 15‐Dec

Week 1  Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 Week 9 Week 10 Week 11 Week 12 Week 13 Week 14 Week 15 Week 16

Phase 1 Phase 1

Design Requirements and Project Scope

Phase 2 Phase 2

Concept Generation

Concept Selection

Phase 3 Phase 3

Detailed Designs

Select Conditioner

Have final solid drawings ready to send to CNH

Have prototype Manufactured

Have prototype installed and ready to test

Phase 4 Phase 4

Software Acquisition and Programming

Testing 

Data Analysis

Data Phases Concepts CNH Testing