Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
1999-09-17
2001-09-04
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C073S009000, C473S200000, C473S222000
Reexamination Certificate
active
06285445
ABSTRACT:
TECHNICAL FIELD OF INVENTION
The present invention generally relates to a method and apparatus for measuring aerodynamic properties of objects, and more particularly of determining the drag and lift coefficients of golf balls in flight.
BACKGROUND OF THE INVENTION
Golf ball manufacturers generally are interested in determining a golf ball's trajectory, which predicts the ball flight distance. Typically, a golf ball's drag and lift coefficients are used to predict the trajectory of the golf ball. Manufacturers have used three techniques for determining a golf ball's drag and lift coefficients. Two conventional techniques use a wind tunnel and the remaining technique uses an indoor testing range.
The first technique uses a golf ball that is supported on a spindle within the wind tunnel. The spindle is affixed to the surface of the ball. The spindle freely rotates on low friction bearings. With the ball immersed in the wind stream, a motor coupled to the spindle spins the ball up to a predetermined spin rate and speed. The motor is disconnected from the spindle, and the ball continues to spin under the influence of its inertia and spin decay rate. The ball's lift and drag are monitored as the ball spins to a stop. The lift and drag are used to determine the trajectory.
This method is problematic for several reasons. First, there is a turbulence level present in the airstream of any wind tunnel, which is not present in the atmosphere through which a golf ball normally flies. Since a golf ball's aerodynamics are fundamentally turbulence driven, this can significantly affect the outcome of the test.
Second, in the wind tunnel the wind stream around the ball is disturbed at the point where the spindle is joined to the ball. This affects the measurements in a way for which it is difficult to compensate.
The second technique also uses the wind tunnel. A ball is spun up to speed outside the tunnel, then dropped into flowing air in the tunnel. The trajectory of the ball is then measured. The problems associated with using a wind tunnel, discussed above also occur using this method. In the second technique, the trajectory needs to be recorded in considerable detail, and the results are probably not highly accurate.
The third technique uses a series of ballistic light screens, where the screens alternate between being vertical or inclined. U.S. Pat. No. 5,682,230 to Anfinsen et al. discloses such an arrangement. When using this set-up, the ball is launched into flight and passes through the series of screens. The orientation of the screens allows the velocity and ball's coordinates to be measured. This information is used to determine the ball's trajectory.
This method is troublesome, because the test set-up requires determining the precise location of each light screen. Locating each light screen involves firing numerous balls. This is undesirable because it is time consuming.
It would therefore be desirable to provide an improved method for determining the drag and lift coordinates of a golf ball, while the ball is in actual flight.
SUMMARY OF THE INVENTION
Broadly, the present invention comprises method for determining the coefficients of lift and drag of a golf ball.
In one embodiment, the method of determining the lift coefficient and a drag coefficient for a golf ball along a flight path includes the steps of providing a launching device for launching the golf ball along the flight path, launching the golf ball along the flight path from the launching device, taking two images of the ball at a first position spaced from the launching device, taking two images of the ball at a second position, using the images at the first position to determine a first measured velocity at the first position, using the images at the second position to determine a second measured velocity at the second position, and calculating the drag coefficient and the lift coefficient using the first measured velocity and the second measured velocity. The method further includes a first and second time interval between taking the images at the first and second positions, respectively, where the time intervals are less than about 0.01 seconds.
In another embodiment of the method, the method includes providing a launching device for launching the golf ball along the flight path; launching the golf ball along the flight path from the launching device, measuring a first measured velocity at a first time and at a first position spaced from the launching device, measuring a second measured velocity at a second time and a second position spaced from the first position, estimating a lift coefficient and a drag coefficient, determining a first predicted velocity at the first position and the first time and determining a second predicted velocity at the second position and the second time, solving a Jacobian matrix to determine a Jacobian solution, calculating a first velocity difference between the first predicted velocity and the first measured velocity and calculating a second velocity difference between the second predicted velocity and the second measured velocity using the lift and drag coefficients, and calculating a new drag coefficient and a new lift coefficient using the Jacobian solution, the first velocity difference and the second velocity difference.
In yet another embodiment, measurements can be taken at more than two positions.
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Gobush William
Winfield Douglas
Acushnet Company
Buczinski Stephen C.
Pennie & Edmonds LLP
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