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					 Putter-Golf Ball Impact
         Literature Review
           November 15, 2004



            Charles Roth
        Charles.roth@colorado.edu

        Advisor: Prof. Zable



  University of Colorado at Boulder
Department of Mechanical Engineering
                                                                                     Roth 1


Intro: Currently there are many golf swing analysis programs on the market, but none

of them use a device that is portable and attached to a golf club. Two companies, Dulles

and MotionCoach, perform swing analysis by video taping the swing from multiple

angles, digitalizing the images, and displaying them on a computer that tracks the path

and speed of the club head. This method is efficient in picking out obvious swing flaws,

but it does not provide specific information about the impact location of the ball and club

head. Titelist has a more advanced system that is able to analyze swing speed, launch

angles, and shaft flex, but like the other systems it is not portable.


The goal of this project is to design a portable device that measures the location of impact

between a golf ball and putter. This project is not so much a research project as it is a

design challenge. Documented work done on this project or similar projects to this is

very limited. Therefore, the focus of my literature review was on various sensing devices

that I may use to collect data in determining the impact location. I also reviewed the

work done here at the University of Colorado by previous students. Though the students

did not meet all of the design requirements, their methods and findings will influence the

approach I take.


Previous Work on “Ping” Project: A group of students did a significant amount of

work on this project. Using an array of photodiodes located along the top face of the

club, they were able to triangulate the impact location. This was done by examining the

voltage outputs from the various individual photodiodes, specifically the intensity of the

readings. The voltage output corresponded to the distance the ball was from the sensor.
                                                                                        Roth 2


Photodiodes with higher readings were closer to the impact location, while a low voltage

output occurred with photodiodes located a larger distance away from impact.



The group designed and constructed a device using an array of 11 Panasonic CNB2001

photodiodes mounted on top of the club head. They then took many readings, moving a

golf ball in 1/10” increments along the face of the club. They used these readings to

determine impact location in test runs.



This system seemed to work fairly well but it had many flaws. The size and mass of the

device exceeded the allowable limit. Also the measurements were not taken in a

controlled lighting environment, which would greatly affect the readings taken by the

sensors. Even if the lighting was controlled in the testing laboratory, it would be difficult

to control it on a golf course, where this device is intended to be used. From these

conclusions I decided to look into other types of sensors, and further into the use of

photodiodes.



Many different types of sensors could potentially be used in collecting data for this

project. The sensors I am currently reviewing and will be testing are accelerometers,

electrostatic proximity detectors, as well as photodiodes. The following information

obtained has helped me determine appropriate selection criteria for each sensor, as well

as whether or not a particular method will be viable.
                                                                                       Roth 3


Accelerometers: Accelerometers are sensors used for measuring, displaying, and

analyzing acceleration and vibration. They can be used individually, or in conjunction

with a data acquisition system. Accelerometers are available in many different forms.

Size, sensitivity, accuracy, a sampling rates vary from one accelerometer to another.

Accelerometers can have from one axis to three axes of measurement, the multiple axes

typically being orthogonal to each other. These devices work on many operating

principles. Below is simple schematic of a typical accelerometer. The common types of

accelerometers are piezoelectric, capacitance, null-balance, strain gage, resonance,

piezoresistive and magnetic induction.




                     Raymond R. Bouche, Endevco Tech Paper 243
                                                                                       Roth 4


There are many important features to consider when selecting a particular accelerometer.

The three main features that must be considered are: amplitude range, frequency range,

and ambient conditions. The acceleration amplitude range is measured in G’s, and

frequency is measured in Hz. For the ambient conditions, temperature should be

considered, as well as the maximum shock and vibration the accelerometers will be able

to handle. For my project, the temperature and maximum shock are not factors, therefore

ordering parts that operate at extreme temperatures, and in extreme conditions is not

necessary. Electrical output options depend on the various systems being used with the

accelerometers. Common analog options are voltage, current, or frequency. For making

higher frequency measurements, such as typical vibration measurements, accelerometers

with a good AC response should be selected. The majority of AC accelerometers use

piezoelectric ceramic or quartz sensing elements which create a charge output (Bouche).



After selecting the proper accelerometer to be used, the mounting method must be

determined. If the motion of the device being measured is not accurately transmitted to

the sensor, it cannot be accurately measured. The most secure method is stud mounting.

In this project though, the accelerometers will be arrange on the putter and drilling on the

club head is not an option. Other possibilities include using a cyanoacrylate adhesive,

such as a super glue, or double-sided tape (Romanchik, 2003). If a glue is used the

stiffness of the cured adhesive is critical to the accuracy of the measurements obtained.

The adhesive should not dampen out the vibrations that are being measured. Though no

adhesive is as stiff as a normal mounting stud, using the proper glue will still yield fairly
                                                                                       Roth 5


accurate results. Whether using glue or tape, the surface must be cleaned thoroughly to

ensure good bonding.



Powering the accelerometer is also a critical issue. In most cases the data acquisition

system will serve as the power source, and supply the necessary current. These cables

attached to the accelerometer must also be carefully dealt with. Flexing of the cables can

create distortions in the data being measure. In order to prevent these errors the cables

should simply be mounted securely, so that they themselves do not vibrate. Lastly,

accelerometers being used should not be overloaded, and need to be calibrated regularly

to ensure accuracy.



Photodiodes: Photodiodes are used to create an electronic signal proportional to the

incident light intensity perceived. These were used by the previous group to determine

the impact location of the ball hitting the flat face of the putter. Advantages to using

photodiodes include the low cost, the small size, and the versatility.



Photodiodes are most often fabricated from silicon semiconductors. The silicon absorbs

light photons, which creates a reaction that can be measured in terms of current

variations. Photodiodes are available in a wide range of shapes and sizes for different

applications. When selecting a photodiode the most important performance

characteristics are response speed, sensitivity, and the size of the active area. For this

particular application the response speed is not significant and the active area is relatively

small, on the order of 1-2 square inches. The sensitivity is the parameter that becomes
                                                                                       Roth 6


important in selecting a proper photodiode. Though the light level will not be

dramatically low, the sensor must be able to adequately pick up small variations as the

golf ball impacts the putter. One advantage in using photodiodes is that many companies

sell prepackaged arrays. This would eliminate the difficult task of creating an array from

individual diodes and integrating them for data acquisition.



Electrostatic Proximity Detectors:       Electrostatic or capacitive proximity sensors

produce an electrostatic field that is able to sense metallic objects as well as nonmetallic

materials. The sensing surface of a capacitive sensor is formed by two metallic

electrodes of an unwound capacitor. As an object nears the surface of the sensor it enters

the electrostatic field of the electrodes which changes the capacitance in the circuit. This

causes oscillation in the component which is measured and ultimately used to determine

the objects location.   This oscillation is proportional to the targets distance from the

sensor. Below is a simple diagram of an electrostatic proximity sensor.




                                 (Diagram from siemens.com)
                                                                                       Roth 7




Proximity detectors such as this are manufactured for many applications. When

selecting a sensor of this type the most important characteristic is the targets that are

specified for the capacitive sensor. This is defined by the dielectric constant of objects

that the sensor can identify. For this project the object is a hardened plastic, so finding an

electrostatic proximity detector that can measure such a material is key. Care must also

be taken to ensure that the sensor is kept dry. Liquid on the sensing surface could prevent

the sensor from operating properly.



Conclusion: From these various reviews I have been able to move forward efficiently.

The work already done on this project has given me a good starting point, from which I

hope to be able to create a working prototype. Understanding better the functionality of

the various sensors has enabled me to select appropriate products to order. Testing these

sensors will ultimately enable me to construct an efficient and accurate working system.
                                                                             Roth 8


                                   Works Cited




Bouche, Raymond R. “Accelerometers For Shock And Vibration Measurements”
      Endevco Technical Paper 243


Koren, Brock. “Photodiodes” OE Magazine, August 2001, pp 34-36


Hultgren, Charlie. “Innovative photoreceivers simplify measurements” Laser Focus
       World, September 1998, pp 123-129


Paisely, Kegan with Alan Prucha, Tim Tetrault, Linda Wikstrom, Adam Zarlengo “Ping
       Project, Design Review” University of Colorado at Boulder, March 3, 2003


Romanchik, Dan. “Seven tips for making better accelerometer measurements,” Test &
     Measurement World, 9/1/2003


Siemens, “Capacitive Proximity Sensors Theory of Operation”   siemens.com