wheel balancing machine

8/12/2019 Wheel Balancing Machine

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Wheel Balancing MachineSubmitted to Dr. Bhat and Dr. Cheung

Patrick Brunelle #5975913, Aerospace and Propulsion, Mechanical Engineering

Andrei Jones #9505792, Aerospace and Propulsion, Mechanical Engineering

Ricky Kwan #5982634, Aerospace and Propulsion, Mechanical Engineering

Joshua Klauber #9554750, Aerospace and Propulsion, Mechanical Engineering (modified?)

Sbastien Parent-Charette #9178821, Software Engineering

10/15/2013


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Table of ContentsTable of Contents 2

Abstract 3

Introduction & Background 4Literature Review 7Design Constraints and Alternative Solutions 10Statement of Work 21Expected Results and Contributions 22Prototype Testing Methodology 22Schedule 23Budget 23Conclusion 25Bibliography 25Table of Figures 26


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AbstractBalancing automotive wheels is an important part of safe and comfortable driving of modern day

road vehicles. Current wheel balancing machines are limited in scope due to a lack of portability

and inexpensive yet precise options. The design proposed here looks to improve in these areas.

Having researched current designs several high cost models with potentially useful features have

been identified. Subsequently an initial idea for a machine was proposed. Now the various

technical challenges involved are being overcome. Design decisions are being made, such as

motor selection, force sensor selection, and mainshaft support structure. Work is being carried

out according to preset task and skill distribution. This should lead to improvements to the

industry. Before the machine can be safely used on the market a set of tests, building up from

simple, single component tests to complex, full machine functionality will be performed. A Gantt

chart and schedule for design and manufacturing are included. The current budgeted cost of this

project is approximately $1300


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Introduction & BackgroundBalancing automotive wheels is necessary because non-uniform mass distribution of a wheel will

cause vibration. The vibration can be severe enough to damage components such as ball joints,

wheel bearings, and the steering linkage. Wheel vibration is a contributor to Noise, Vibration and

Harshness (NVH).

The objective of this capstone project is to create an automatic wheel balancing machine for

wheels from automobiles, motorcycles, and ATVs. The machine shall be able to measure and

correct both static and dynamic imbalance of a wheel. Properly balanced wheels contribute to a

smooth ride at high speed. Here are our general design criteria:

Ensure the safety of the machine operator Make the machine durable and high quality Make the machine lightweight and inexpensive Make the machine easy to use

General Specifications (subject to change)

Maximum wheel weight 75 lbs

Balancing RPM Continuously variable, 500 RPM max

Gearmotor type hp, 90 VDC, permanent magnet, brushed

Power supply 120 VAC, 50/60 Hz (240 VAC with small modifications)

Enclosure construction plywood


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Figure 1: Initial Conceptual Sketch

Figure 2: Lego Maquette


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Typical Wheel Balancing Procedure:

1. Install the wheel on the end of the mainshaft.2. Manually enter the coordinates of the desired balancing mass locations.3. Close the safety cover.4. The machine will rotate the wheel, record the vibration forces, and calculate a

Balance Solution. The balance solution is the combination of balancing masses and

installation locations that will balance the wheel.

5. When the wheel stops spinning, lift the safety cover.6.

The machine will present the balance solution to the operator.

7. Rotate the wheel manually to the correct angles, and install the balancing masses asper the balance solution.

8. Begin another balancing cycle to confirm that the wheel is balanced. A high-qualitybalancing job may be an iterative process.


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Literature ReviewMarket Analysis:

Looking at the website of HunterEngineering Company. Hunter is a well-known brand of

automatic wheel balancer. Below are the features provided with the cheap, midgrade, and

expensive wheel balancers:

- Cheap model (DSP7705) Basic static & dynamic balancing. Display panel. Arm for semi-automated balancing mass coordinate entry. Move the arm until the

end touches the desired balancing mass mounting locations. Using position

sensors on the arm, the balancing mass coordinates can be read by the machine.

- Midgrade model (SmartWeight Touch SWT22) Touchscreen interface. Laser indicator that shines on the wheel/tire assembly to indicate 12 o-clock

angular position.

Printer output. Data/results can be sent to a printer.- Expensive model (ForceMatch HD FM03)

Wheel lift to raise the wheel off the ground and onto the mainshaft. This is toreduce the risk of injuries from heavy lifting.

Correction for out-of-round error. A roller follower applies radial force to thewheel, and the roller followers movement is recordedby the machine.


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Scientific research:

These equations are conditions for wheel balance. Assume a Cartesian coordinate

system, with the z-axis collinear with the shaft centerline.

= 0and = 0(1 pp. 222-223) for static balance = 0and = 0 (1 p. 497)for static and dynamic balance

This is an equation for the equivalent spring constant at the wheel mounting location. This was

derived from equations found at the listed source:

= 34128 (2 pp. 530-539) where L is the distance between support bearings and thedistance from the center bearing to the wheel mounting location.

Rewriting the standard natural frequency formula to give a result in RPM:

= 3(3 p. 134)ACME Threads will be used for mounting the wheel-holding components on the mainshaft.

Standard dimensions for 1-10 ACME threads were found on the ATI Metals website. (4)

For appropriate bearing mounting fits, the following information was used:

NTN Corporation uses glass-reinforced polyester. (5) One way to select bearing fits was shown in NTN Corporation documentation. (6) AST Bearings offer an excellent resource for selecting bearing fits. (7)


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The only problem is a lack of data on appropriate fits for plastics. To compensatefor plastics greater compliance (versus metal), the plastic will be given a tighter

fit. The load will be fixed (a non-reversing load) relative to the plastic bearing

housing, which will make the bearing housing fit not so critical.

Mainshaft bearing information (R20 size):

The specifications were taken from the supplier sourcing documentation (8)subsequent to purchase; real measurement of the components will be used.

Electronic components:

For all electronic components their datasheets were used (See Mini-PDM)


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Design Constraints and Alternative Solutions- There is a potential safety risk with the wheel spinning at 500 RPM. A wheel cover will be

included to guard the spinning wheel, but what happens if someone tries to open the cover?

Braking the rotating assembly to a rapid stop may be possible. Unfortunately, thewheels polar mass moments of inertia are unknown, and a brake adds extra

complexity to the project.

A computer-controlled wheel cover interlock will prevent opening the cover until themainshaft is stopped. There is some added complexity in this case, but the wheel

cover interlock requires relatively little integration with the rest of the project,

simplifying project management. Also, the unknown wheel inertia is no longer a

concern. A wheel cover interlock was chosen.

- Wheel rotation direction. Because there will be dynamic braking, peak torque applied to thewheel (by the mainshaft) should be close to equal in either direction. Therefore, there is no

preferred direction in terms of the wheel retaining nut loosening. Wheel directions are

defined looking at the wheel, with the motor behind:

CCW CW: If the mainshaft snaps during rotation, and the spinning wheel falls to the

ground, it should continue rolling to the rear, away from the operator. Due to this

CW rotation was chosen.


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Figure 3: Wheel Rotation Schematic

- Question: What range of mass imbalance do we want to measure? This will affect: Balancing RPM range Force sensor sizing Motor hp rating Smallest possible detectable imbalance

- Question: How much wheel backspacing do we want to accommodate? This will affect: The cantilever length of the shaft. Too much cantilever length will reduce the shafts

critical RPM.

With a short cantilever length, the range of wheels that can be accommodated will belimited. High backspace wheels, such as sports car wheels (such recent-model

Corvette rear wheels) may not fit.


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Figure 4: Backspacing (Edited from source image) (9)

- Constraint: We want the machine to be heavily ballasted for stability, but low in weight forportability. What ballasting options do we have?

Fixed weight, such as concrete. This makes the machine heavy. Sandbags. These are removable for transport, easing the load necessary but requiring

several trips to and from the area where one wants to move the machine.

Water tank ballasting. The tanks will be emptied for transport and filled with water inplace to make the machine stable. This will allow for easy transport but requires a

source of water at the destination. Water tank ballasting was chosen.

- Wheel mounting scheme

Rear cone: Uses several parts, gives more flexibility in wheel mounting.


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Figure 5: Rear Cone Mounting (10 p. 11)

Front Cone: Less parts, and will likely suffice for most wheels. A front conemounting system was chosen.

Figure 6: Front Cone Mounting (10 p. 11)


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- Shaft drive type. The shaft must be driven with a pure torque, and no other force reactionsare permissible.

Belt drive. This offers (useful) speed reduction, but it is difficult to arrange the beltgeometry so that the belt tension resultant force is always perpendicular to the force

sensing direction. This introduces possible inaccuracies.

Flex coupling. There are several types of varying stiffness. Some of the more flexibleones are made of rubber, but with temperature changes, the rubber may change shape

and apply unwanted forces to the mainshaft. The more flexible rubber couplings are

also limited in torque capability.

A telescopic double u-joint. An inexpensive steering intermediate shaft from a carcan provide the necessary degrees of freedom along with structural stability. This

was selected. One was taken from a 2001 Saturn in a junkyard. It is meant to work

with shafts that have two flats (not hard to machine). Because it was a steering shaft,

it is able to handle the torque of a grown man twisting the steering wheel in an

emergency situation without breaking. This torque is likely less than the torque of a

mechanic torqueing the wheel retaining nut (on the end of the mainshaft) with a

wrench.

- Motor type AC Induction: Most obtainable, but a variable speed motor drive will be expensive. AC Synchronous: A variable speed motor drive will be expensive, but speed control

will be accurate. However, we dont need accurate speed control, since we can

measure the RPM via the optical encoder.


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DC: The variable speed drive for a DC motor is inexpensive. The only issue is brushreplacement, but for the small number of service hours this balancer is expected to

see, brush life should not be a problem. We chose a permanent magnet DC

gearmotor.

- Optical encoder positioning Incremental: An incremental encoder measures the change in angular position

relative to some starting position. This will possibly require an angular position

zeroing procedure every time the machine is used. A quadrature incremental encoder

using two tracks is able to distinguish direction.

Absolute: An absolute encoder measures the absolute angular position of the shaft.Each angular position is unique and distinct from any others. When the wheel

balancer is turned off, the current position will not be lost as with an incremental

encoder. With 8 tracks, we will be able to distinguish 2^8 = 256 unique positions.

We are using an 8-bit absolute encoder.

- Optical encoder disk placement Gearmotor tailshaft: The tailshaft of the gearmotor has a keyway, which would make

it easy to install an encoder disk. Furthermore, many off-the-shelf optical encoders

are intended for use at the end of a shaft; few are made hollow for a thru-shaft. Since

we selected an absolute position encoder, we cannot install the encoder disk on the

tailshaft. The gear reduction of the gearmotor prevents us from being able to

distinguish unique mainshaft positions.

Gearmotor output shaft: With this placement one can distinguish unique mainshaftpositions; however, there is too much angular play in the telescopic double u-joint, so


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the encoder readout here will not track the mainshaft position accurately enough.

This angular play problem would also be a problem for a tailshaft-mounted encoder

disk.

Mainshaft: We will install the encoder disk on the mainshaft. This solution willrequire more integration work, and this will have to be a custom encoder disk, rather

than an off-the-shelf unit.

- Optical encoder position coding Binary: The output of the encoder increments in a natural counting order:

00, 01, 10, 11 (2-bit example)

The problem with binary is that 2 or more bits may change at a time between

adjacent positions (such as 01-to-10). If the different bits do not change at exactly the

same angular positions, there can be erroneous readings at some angular positions.

Gray: The output of the encoder increments in Gray code:00, 01, 11, 10 (2-bit example)

The most important property of Gray code for our purpose is that only one bit

changes at a time between adjacent positions. This will make the encoder position

output monotonic with position. Gray code also simplifies some supporting logic that

may be used with the encoder.

- Optical encoder disk type

Transmissive: A disk is machined with holes. Position is determined by the

transmission of light through the disk. Alignment between light emitters and

receptors is important. Holes in the disk may adversely affect balance.


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Reflective: A disk is made with light/dark sections. Position is determined by thereflection of light shined on the disk. Since there are no through-holes, the disk will

be stiffer. Combined emitter-receptors simplify design and alignment concerns.

- Optical encoder receptor type Photocell: Slow, rarer. Phototransistor: Phototransistors are sensitive to light. For the encoder, high

sensitivity to light is not desired. The encoders own light emitters should be bright

enough to swamp out the effects of any ambient lighting.

Reverse-biased photodiode: Reverse-biased photodiodes have fast response. Thiswill minimize angular phase error during mainshaft rotation. A photodiode and

590 nm LED combination in a single through-hole package was chosen.

- Bearing housing support. The bearing housings must be restrained with 1-DOF (translation)each. Motion in the remaining DOF will be restrained by the force sensors.

Linear bearings: Some linear ball bearing carriages were purchased, and they had toomuch friction. This idea was scrapped.

5-link setup: 5 properly arranged links (with spherical rod ends) can restrain anobject in space except for 1 remaining DOF. Adjustable link lengths offer more

options in terms of aligning the bearing housings.


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Figure 7: 5-Link Bearing Housing Support

- Raw material and form for bearing support links Plastic: Easy to machine, but low modulus of elasticity is likely to promote buckling

in the compression links.

Metal: Sufficiently stiff. Tubing: Harder to find, but a variety of sizes are available. Pipe: Schedule40 black pipe will be suitable. When used with male 7/16-20 UNF

rod ends, the ends of the pipe can tapped to accept the rod ends. In fact, the pipe ID

is close enough to the tap drill size that no pre-drilling is necessary. Pipe is typically

easy to find.


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- Bearing housing material. Aluminium: Good stiffness, strength, medium machining difficulty. Steel: Stiff, strong, hardest to machine. Nylon: Inexpensive, but there are dimensional changes with humidity changes,

which are likely to make the bearings fit incorrectly.

Polyester: Harder to find Any glass-filled plastic: Hard to machine, may wear out tools rapidly. PVC: Good chemical resistance, and the group has experience machining PVC. We

will first try with PVC. PVC sheet is also available on-hand, and can be glued to full

strength.

- Force Sensor Type/Packaging S-beam: An S-beam sensor can measure both tension and compression. Finding

sensors for small force ranges can be difficult/expensive.

Compression-only button cell: Compression-only cells are cheaper, so this is whatwe went with. To measure tension, we will bias the load cell to 50% Full Scale using

a preload spring. The constant preload will also take up any slack between the

bearing housing and force sensor. We selected a surface-mount force sensor, to be

installed on a custom-made printed circuit board.

Figure 8: Force Sensor (11)


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Statement of WorkPatrick Brunelle is the team manager. His skills include analog electronics, general mechanical

design, and leadership of small groups.

Andrei Jones has previous experience with bearings and bearing mountings. His skill set includes

organization, communication, CNC programming, welding, machining and manufacturing. His

understanding of scientific principles enables him to contribute to the conceptual stage of the

design, and his organizational/communication skills will enable him to maintain the

documentation.

Joshua Klaubersknowledge in mathematics, physics and heat transfer will enable him to

contribute to the motor/braking system of the machine. In addition, his organizational,

communication and language skills will benefit the project documentation.

Ricky Kwan is the team draftsman, as well as being the intermediary with school administration.

His technical understanding will also prove useful in manufacturing.

Sbastien Parent-Charrette has knowledge in digital electronics, robotics, and embedded

systems. He will be the major contributor to the microcontroller/software/user interface

component of the project.


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Expected Results and ContributionsThe overall expected result of this project will be anywhere between a fully functional and safer

wheel balancer than existing designs, to one that is also lighter, portable, and easy to use (time

constraints may limit the advancements that can be made). These advancements would also be

the contributions to the industryan improvement on current designs.

Prototype Testing MethodologyOne advantage to this project is the simplicity of testing the tool in the prototype phase. This will

involve making a special test disk with holes. Then, precise testing masses will be installed in the

test disk. The wheel balancer should be able to measure and calculate the placement and mass of

an appropriate counterweight. The calculated counterweight should be equal in mass to the test

weight, and 180 away.

- Tests will be done in the following order: Motor alone Shaft and bearing assembly, hand rotation of the bearings to check for

binding/roughness

Motor and shaft assembly connected to each other Shaftbearing assembly, dummy load, no motor, ensuring data detection Testing the software in the microcontroller Safety feature checking Final testingwhere full functionality of the final assembly is performed


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ScheduleOur preliminary timetable was to have a preliminary design by September, leaving time to

manufacture the initial prototype in time for Christmas. In January, iteration of the design based

on observations of the machine will be done.

Figure 10: Gantt Chart

BudgetAn estimate of the required parts is in table below:

Quantity Description Unit Price Extended Price

8 Optical Sensor 6.39 51.12

2 Force Sensor 63.50 127.00


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1 Dynamic Braking Resistor 21.98 21.98

1 Dynamic Braking Resistor Hardware Kit 8.64 8.64

1 Electric Motor 97.44 97.44

1 Motor Controller 50.00 50.00

2 Shaft Support Ball Bearings 30.28 60.56

1 Saturn Steering Shaft 8.61 8.61

1 CPU Heatsink & Ferric Chloride 34.47 34.47

1 2 Mushrooms + AGC Fuseholder + Octal Relay

Socket

25.20 25.20

4 Black Workbook 8.04 32.15

1 Power Switch 7.36 7.36

1 Relay 14.21 14.21

1 Relay Socket 8.11 8.11

2 Relay Hold-Down Clips 0.51 1.02

1 Resistor Enclosure 40.23 40.23

1 Levelling foot base mount (box of 25) 8.09 8.09

4 Feet 7.26 29.04

Miscellaneous/other 600 600

SUM $1225.33


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ConclusionIn conclusion, the project is moving along and the technical complications are beginning to

reveal themselves. As of yet tasks are being handled by the team and the project is advancing.

Bibliography1. Beer, Ferdinand P., Johnston, E. Russell Jr. and Eisenberg, Elliot R.Vector Mechanics

for Engineers. 8th. New York, NY : McGraw-Hill, 2007.

2. Beer, Ferdinand P., et al.Mechanics of Materials. 5th. New York : McGraw-Hill, 2009.

3. Rao, Singiresu S.Mechanical Vibrations. 5th. Upper Saddle River, NJ : Prentice Hall, 2011.

4. ATI Metals.[Online]

http://www.atimetals.com/products/Documents/TC_AcmeThreadforms.pdf.

5. NTN Corporation.[Online] 08 2013. http://www.ntn-snr.com/portal/de/de-

de/file.cfm/buplastic3904iiie.pdf?contentID=5523.

6.. [Online] 2013. http://www.ntnamericas.com/en/pdf/2200/brgfits.pdf.

7. AST Bearings.[Online] http://www.astbearings.com/assets/files/Technical-Information-

Sheet--Radial-Ball-Bearings-Fitting-and-Mounting--ENB-04-0638.pdf.

8. McMaster-Carr.[Online] http://www.mcmaster.com/#60355kac/=ovs4zi.

9. Colorado Components.[Online] http://cocomponents.com/dealer/wp-

content/uploads/2012/04/ATV-Wheel-Offset-Explaination.jpg.

10. Ranger Products.Bendpak.com. [Online] http://www.bendpak.com/ZR-

650%20REV%20A.pdf.

11. Digikey.[Online] http://media.digikey.com/Photos/Honeywell%20Photos/FSS1500NGT.jpg.


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Table of FiguresFigure 1: Initial Conceptual Sketch ................................................................................................ 5Figure 2: Lego Maquette ................................................................................................................. 5Figure 3: Wheel Rotation Schematic ............................................................................................ 11Figure 4: Backspacing (Edited from source image) (9) ................................................................ 12Figure 5: Rear Cone Mounting (10 p. 11)..................................................................................... 13Figure 6: Front Cone Mounting (10 p. 11) ................................................................................... 13Figure 7: 5-Link Bearing Housing Support .................................................................................. 18Figure 8: Force Sensor (11) .......................................................................................................... 19Figure 9: Overload Protection Scheme ......................................................................................... 20Figure 10: Gantt Chart .................................................................................................................. 23