Senior Design:Tachometer Calibration Device

Team 4: Jennifer Egolf, Matthew Hagon, Michael Lee, Christopher Pawson

Sponsor: DuPont

Advisor: Dr. Glancey

Mission Statement

Design and manufacture a portable device for

the relative calibration of multiple surface

tachometers.

Surface Tachometers

Shaft

Encoder

Wheel Bracket

Surface Tachometers

V1 V2 V3 V4

Surface tachometers measure surface velocity

Detect small differences in speed across a system

Calibrated tachometers used as diagnostic tools

Reduce downtime of continuous processes

V1=V2=V3=V4

Desired Features with Metrics

Constant Speed % Variation in Speed

Portable Size / Weight

Ease of Use Set up time

Adaptable # of tachometers mounted

Adjustable # of attainable speeds

Durable # of cycles until failure

Inexpensive Cost

Wants Metrics

Benchmarks

High inertia devices Lathe

Current method used + Low variation in speed - Only accommodates one tachometer at a time - Cannot calibrate tachometers relative to one another - Not portable

Drum Previous method employed for calibration + Low variation in speed - Large and not portable

Hand-held calibration devices + Portable - Cannot calibrate tachometers relative to one another

Initial System Concept

Tachometers

User interface

Motor Controller

Motor

Tachometer mounting brackets

Subsystem Configuration

Three concepts for the critical subsystem were developed through benchmarking and brainstorming

Conveyor Belt Rotating Disc Rotating Drum

Metrics and Target ValuesDesign Specifications

< $20,000

> 105

at least 3

< 5 minutes

4

< 0.05%

< 3' x 3' x 3' & < 90lbs

0 5 10 15 20 25 30 35 40

% of speed variation

size & weight

# of tachometers mounted

set up time

# of attainable speeds

# of cycles until failure

cost

Met

rics

Rate of Importance (%)

Concept Selection

•Advantages

•Easy to mount multiple tachometers

•Disadvantages

• Vibrations associated with belt and linkage joints

• Difficult assembly

•High cost

•Advantages

•Ease of assembly

•Consistent performance

•Low cost

•Disadvantages

•Machining accuracy of disc crucial

•Advantages

•Ease of assembly

•Consistent performance

•Easy to mount multiple tachometers

•Disadvantages

• Large / Heavy

•Machining accuracy of drum crucial

Conveyor Disc Drum

Choosing the Best Solution

The disc was chosen as the best concept because:

Easy to assemble Consistent performance throughout life Low Cost Smallest / Least material

Chosen Concept of Subsystem

Tachometers

Motor & Gearbox

Tach mounts

Disk and Shaft

System Component Considerations

Tachometer mounts Positioning

Must be able to accommodate tachometers of circumference:• 6”• 12”• 30”

Disc Dimensional variability

Motor and Controller Selection Speed

Must be able to achieve specified surface velocities• 16 fpm• 110 fpm• 240 fpm

Torque Inertia Ripple

Motor and Controller

SGDH Servo Drive

Yaskawa SGMPH Servo Motor

Power requirements Start-up torque = 0.66 N-m

Inertia requirements System Inertia = 0.03 kg-m2

Speed requirements Three speed options

12 rpm 84 rpm 183 rpm

Velocity Ripple

Velocity Ripple

Fluctuations around the steady state velocity

Exact relationship between motor speed and % velocity ripple unknown 100 rpm: ± 5% Above 1000 rpm: <1%

Need to maintain high motor speeds but output relatively low disc speed Solution Gearbox

Gearbox Selection

Allows motor to run at optimal speeds 1000 - 5000 rpm

CGI, Inc. Planetary Gearbox 22:1 ratio

Motor speed of 2000 rpm = Disc speed of 91 rpm

Motor speed of 4000 rpm = Disc speed of 182 rpm

Design of Subsystem Components

Disc 5” diameter 2” thickness Machined in house

Tachometer mounts Purchase framing

materials from Bosch Machine mounting

blocks in house

Eccentricity Testing

Results: 0.0005” < variations <0.001” Create variations in speed

< 0.02%

Positioning Testing

Prototype

Locking handle

Gearbox

Motor

Tachometer

Disc and shaft

Slider Carriages

* Controller and user interface not pictured

Testing Method

Mount tachometer to rotating disc

Record speed variations over time

Peaks on graphs indicate Amplitude of recurring

speed variations Frequency of speed

harmonics

Time

Spe

edA

mpl

itude

Frequency

Speed in Time Domain

Speed in Frequency Domain

Full System Testing

Testing of the system revealed Large variations in

speed Many frequencies

Need to determine cause of variations

Spe

ed A

mp

litu

de

Speed

Tachometer speed variations from disc:

Testing of Motor and Gearbox

Remove disc and shaft Mount tachometer

Directly to shaft of gearbox Directly to shaft of motor

Record speed variations for each case

Tachometer speed variations with gearbox:

Tachometer speed variations without gearbox (just motor effect):

Direct Drive System Testing

Objective: Confirm that the gearbox is

the problem source (not bearings or coupling)

Procedure: Mount tachometer to directly

driven shaft Record variation in speed

Results: 0.2 – 0.6% speed variation Located at a distinct

frequency

Speed

Spe

ed A

mp

litu

de

Tachometer speed variations with directly driven shaft:

Similar variations to motor testing

Observations

The purchased gearbox is inappropriate for the application Creates many and large speed

variations (2.5%) Multi-stage construction

creates problems

The purchased motor exhibits acceptable performance Speed variations few and small (0.2%)

Recommendations for Further Development

Eliminate multiple stage gearbox Test system using worm gearbox Consult custom gearbox manufacturers

Rino GAM Andantex

Expense Summary to Date

Item Quantity Cost

Motor and Drive System 1 $3100

Bearings-NTN pillow block 2 $70

Coupling 1 $100

Gearbox 1 $540

Aluminum Bosch profile 3800 mm $190

Bosch Accessories Many $690

Total Cost 1 ~ $4700

* $1500 under budget – use toward carrying out recommendations for further development

Questions?