Method and apparatus for determining the performance of sports bats and similar equipment

• US 5,672,809 A
• Filed: 02/29/1996
• Issued: 09/30/1997
• Est. Priority Date: 02/29/1996
• Status: Expired due to Term

• Current Assignee: Richard A. Brandt
• Original Assignee: Richard A. Brandt
• Inventors: Brandt, Richard A.
• Primary Examiner(s): Dougherty, Elizabeth L.
• Application Number:
  US08/608,672
• Time in Patent Office: 579 Days
• Field of Search: 73/12.02, 73/12.09, 73/65.03, 73/11.01, 473/422, 473/451, 473/468, 473/563, 273/107, 124/16, 124/34, 124/55, 124/65
• US Class Current: 73/12.01
• CPC Class Codes: G01N 3/52 by measuring extent of rebound of a striking body G01N3/54 takes precedence
• CPC Class Codes: G01N 33/008 Sport articles, e.g. balls, skis or rackets

Abstract

A system for determining the performance of a first piece of sport equipment mounts the first piece of sports equipment such as a bat, golf club, tennis racket, or hockey stick having known characteristics of a Moment of Inertia, a weight, and a location of a Center of Mass for impact by a second piece of sports equipment which has a known Coefficient of Restitution in a mounting device. The mounting device is arranged to freely move the first piece of sports equipment from a predetermined starting position when the first piece of sports equipment is impacted substantially at a center of a predetermined impact area thereof by the second piece of sports equipment moving at a velocity "v". A measuring device measures (a) the velocity "v" of the second piece of sports equipment propelled at the center of a predetermined impact area, and (b) the rebound velocity "V" of the first piece of sports equipment as the first piece of sports equipment moves after it has been impacted by the second piece of sports equipment. The known characteristics of the first and second pieces of sports equipment and the rebound velocity of the first piece of sports equipment and the velocity of the second piece of sports equipment are used to determine a Coefficient of Restitution (COR) between the first and second pieces of sports equipment, and a performance factor for the first piece of sports equipment.

Claims

1. A method of determining a performance of a first object comprising known characteristics of a Moment of Inertia, a weight, and a location of a Center of Mass, the method comprising the steps of:

(a) causing an impact between the first object and a second object so as to cause the first object to rebound, the second object having known physical characteristics including a known Coefficient of Restitution, and a predetermined velocity relative to the first object just before the impact;

(b) measuring the velocity of the first object during the rebound thereof from the impact;

(c) determining a Coefficient of Restitution between the first and second objects using the rebound velocity of the first object measured in step (b) and the predetermined velocity of the second object; and

(d) determining a performance factor for the first object from the known characteristics of the second object and the Coefficient of Restitution between the first and second objects determined in step (c).

2. The method of claim 1 further comprising the steps of:

(e) prior to performing step (a), rotatably mounting the first object for free rotation in a predetermined plane; and

(f) in performing step (a), causing the second object to impact the first object normal to an axis of rotation of the first object in the predetermined plane of rotation and in a predetermined impact area of the first object.

3. The method of claim 1 wherein in step (a) causing the second object to have a substantially non-spin impact on the first object.

4. The method of claim 1 further comprising the step of:

(e) prior to performing step (d), determining the rebound velocity of the second object after impact with the first object in a game condition.

5. A method of determining a performance of a first object comprising a known Moment of Inertia about a predetermined rotation point impacting a second object which has known characteristics including a known Coefficient of Restitution, the method comprising the steps of:

(a) rotatably mounting the first object at the predetermined rotation point;

(b) causing the first and second objects to have essentially non-spin impact so as to cause the first object to rotate and the second object to rebound after the impact;

(c) measuring the velocity of the second object relative to the first object before the impact of the two objects;

(d) measuring the velocity of the first object after impact with the second object;

(e) determining the Coefficient of Restitution between the first and second objects using the measured velocities from steps (c) and (d); and

(f) determining a performance factor for the first object from the known characteristics of the second object and the Coefficient of Restitution between the first and second objects.

6. A method of determining a performance of a first piece of sports equipment having a Moment of Inertia "I" about a predetermined axis of rotation thereof that is used to strike a second piece of sports equipment having a weight "w" and a predetermined Coefficient of Restitution comprising:

(a) mounting the first piece of sports equipment at the predetermined axis of rotation thereof in a mounting means, the mounting means being arranged to allow the first piece of sports equipment to freely rotate from a stationary predetermined starting position when the first piece of sports equipment is impacted substantially normal to a longitudinal axis thereof and substantially at a center of a predetermined impact area thereof by the second piece of sports equipment;

(b) causing the second piece of sports equipment to be propelled with a velocity "v" at the center of the predetermined impact area of the first piece of sports equipment;

(c) measuring the velocity "v" of the second piece of sports equipment with a first measuring means; and

(d) measuring the velocity "V" of the first piece of sports equipment with a second measuring means as the first piece of sports equipment rotates about its axis of rotation from being impacted by the second piece of sports equipment for determining a Coefficient of Restitution between the first piece of sports equipment and the second piece of sports equipment, and a performance factor of the first piece of sports equipment.

7. The method of claim 6 wherein a rebound velocity "v'"'"'" of the second piece of sports equipment is determined from the expression v'"'"'=(IV^a /wR)-v, where V^a is the angular speed of the first piece of sports equipment measured at a radial distance R'"'"' over a distance d'"'"' for a time T'"'"' after the first piece of sports equipment is impacted by the second piece of sports equipment, I is the Moment Of Inertia of the first piece of sport equipment about its axis of rotation, w is the weight of the second piece of sports equipment, and R is the distance between the axis of rotation of the first piece of sport equipment and the impact point of the second piece of sports equipment on the first piece of sports equipment.

8. The method of claim 6 further comprising the steps of:

(e) in performing step (c), measuring the time T that it takes for the second piece of sports equipment to travel a first predetermined distance "d" in order to determine the velocity "v"; and

(f) in performing step (d), measuring the time T'"'"' that it takes for the first piece of sports equipment to radially travel a second predetermined distance "d'"'"'" at a third predetermined radial distance "R'"'"'" after the first piece of sports equipment is impacted with the second piece of sports equipment in order to determine the velocity "V".

9. The method of claim 8 further comprising the steps of:

(g) prior to performing step (a), making a test calibration by mounting a correspondingly-shaped first piece of sports equipment which has a predetermined weight=W_o and a predetermined Moment of Inertia=I_o at its predetermined axis of rotation thereof in the mounting means, where the predetermined weight W_o of the correspondingly-shaped first piece of sports equipment is at least three times heavier than the weight W of the first piece of sports equipment to be tested and a surface of the correspondingly-shaped first piece of sports equipment is flat and incompressible where the second piece of sports equipment having a weight=w_o and a Coefficient of Restitution=e_o impacts the correspondingly-shaped first piece of sports equipment;

(h) performing step (c) to measure a time T_o for the second piece of sports equipment to travel the first predetermined distance "d", while concurrently performing step (c) to measure a time "T'"'"'_o " for the correspondingly-shaped first piece of sports equipment impacted at a distance=R_o from its predetermined axis of rotation to radially travel a second predetermined distance=d'"'"' at a third predetermined radial distance=R'"'"' from its predetermined axis of rotation; and

(i) determining the ratio d'"'"'/dR'"'"' from the expression d'"'"'/dR'"'"'=(1+e_o)/ (R_o +I_o /w_o R_o) (T_o /T'"'"'_o)!.

10. The method of claim 9 further comprising the step of:

(j) determining a performance factor "PF" for the first piece of sports equipment to be tested that has an Moment of Inertia=I and is impacted at a distance "R" from its axis of rotation by the second piece of sports equipment having a weight=w and a predetermined Coefficient of Restitution=e from the expression

space="preserve" listing-type="equation">PF= (1+I/wR.sup.2)(d'"'"'/dR'"'"')(RT/T'"'"')-I!/e.sub.o.

11. The method of claim 6 wherein the second piece of sports equipment is a ball and in performing step (b) propelling the ball with substantially no spin thereon at the center of the predetermined impact area of the first piece of sports equipment.

12. A system for determining a performance of a first object comprising known characteristics comprising a Moment of Inertia, a weight, and a location of a Center of Mass, the system comprising:

impact causing means for causing an impact between the first object and a second object so as to cause the first object to rebound, the second object having known physical characteristics including a known Coefficient of Restitution, and a predetermined velocity relative to the first object just before the impact; and

measuring means for measuring the velocity of the first object during the rebound thereof from the impact such that a Coefficient of Restitution between the first object and the second object can be determined, and a performance factor for the first object can be determined from the known characteristics of the second object and the Coefficient of Restitution between the first object and second objects.

13. The system of claim 12 further comprising:

means for rotatably mounting the first object for free rotation in a predetermined plane; and

the impact causing means causes the second object to impact the first object normal to an axis of rotation of the first object in the predetermined plane of rotation and in a predetermined impact area of the first object.

14. The system of claim 12 wherein the impact causing means causes the second object to have a substantially non-spin impact with the first object.

15. The system of claim 12 further comprising means for determining the rebound velocity of the second object after impact with the first object in a game condition.

16. A system for determining a performance of a first object comprising a known Moment of Inertia impacting a second object which has known characteristics including a known Coefficient of Restitution, the system comprising:

mounting means for rotatably mounting the first object such that the first object will rotate when the first and second objects impact each other;

means for causing the second object to have a non-spinning impact with the first object so as to cause the first object to rotate and the second object to rebound after impact;

first measuring means for measuring the velocity of the second object relative to the first object before the impact of the two objects; and

second measuring means for measuring the velocity of the first object after impact with the second object so as to determine a performance factor for the first object.

17. A system for determining a performance of a first piece of sports equipment having a known Moment of Inertia "I" about a predetermined axis of rotation thereof that is used to strike a second piece of sports equipment having a weight "w" during the playing of a sports game comprising:

mounting means for mounting the first piece of sports equipment at the predetermined axis of rotation thereof, the mounting means being arranged to freely rotate the first piece of sports equipment from a stationary predetermined starting position when the first piece of sports equipment is impacted substantially normal to a longitudinal axis thereof and substantially at a center of a predetermined impact area thereof by the second piece of sports equipment moving at a velocity "v"; and

measuring means for measuring (a) the velocity "v" of the second piece of sports equipment propelled at the center of a predetermined impact area, and (b) the velocity "V" of the first piece of sports equipment as the first piece of sports equipment rotates about its axis of rotation after it has been impacted by the second piece of sports equipment for determining a Coefficient of Restitution between the first piece of sports equipment and the second piece of sports equipment, and for determining a performance factor for the first piece of sports equipment.

18. The system of claim 17 further comprising propelling means for propelling the second piece of sports equipment at the velocity "v" and aimed substantially at the center of the predetermined impact area of the first piece of sports equipment to be measured.

19. The system of claim 18 wherein the second piece of sports equipment is a ball and the propelling means is a gas cannon that propels the ball with substantially no spin thereon at the center of the predetermined impact area of the first piece of sports equipment to be measured.

20. The system of claim 19 wherein the gas cannon comprises:

a tube defining each of a cylindrical longitudinal bore that cross-sectionally substantially matches an outer shape of the ball to be propelled therefrom, an inlet port at a first end thereof for selectively receiving a gas at a predetermined pressure into the bore, and a plurality of apertures disposed around a predetermined portion of the tube, the tube having a circumference selected to house the ball therein prior to being propelled from the gas cannon;

first and second pistons being coupled together by a coupling member and being disposed within the bore of the tube for longitudinal movement with the first piston being located closer to the inlet port than the second piston, the second piston comprising a major surface for cradling the ball without the ball touching a surface of the bore when the ball is propelled from the bore;

a baffle comprising an outer surface which fixedly engages the surface of the bore of the tube at a predetermined location between the apertures defined in the predetermined portion of the tube and the second piston to divide the bore into two parts, the baffle defining an aperture through which the coupling member is able to move when the first piston is caused to move by the gas entering the inlet port of the tube; and

the plurality of apertures being disposed so as to facilitate the escape of any gas in the bore of the tube between the baffle and the first piston while the first piston is located between the inlet port and the plurality of apertures, and for facilitating the escape of gas introduced into the inlet port when the first piston is between the plurality of apertures and the baffle.

21. The system of claim 19 wherein the propelleing means comprises:

a structure having sidewalls which define a bore having a cross-section that is selected so as to facilitate movement of the object through a portion thereof;

a piston arranged for movement within the bore with a surface thereof having a contour shaped to cradle the object when the object is propelled out of the bore after being placed therein;

accelerating means for causing the piston to be accelerated so as to cause the object to be cradled on the surface of the piston and propelled out of the bore without touching the sidewalls of the bore; and

decelerating means for subsequently causing the piston to be decelerated.

22. The system of claim 17 wherein the measuring means comprises:

a first velocity measuring device for measuring the velocity "v" of the second piece of sports equipment prior to the impact thereof with the center of the predetermined impact area; and

a second velocity measuring device for measuring the velocity "V" of the first piece of sports equipment after the first piece of sports equipment has been impacted by the second piece of sports equipment at the center of the predetermined impact area as the first piece of sports equipment rotates about its axis of rotation.

23. A gas cannon for propelling an object placed therein comprising:

a structure having sidewalls which define a bore having a cross-section that is selected so as to facilitate movement of the object through a portion thereof;

a piston arranged for movement within the bore with a surface thereof having a contour shaped to cradle the object when the object is propelled out of the bore after being placed therein;

accelerating means for causing the piston to be accelerated so as to cause the object to be cradled on the surface of the piston and propelled out of the bore without touching the sidewalls of the bore and with substantially no spin thereon; and

decelerating means for subsequently causing the piston to be decelerated.

24. The gas cannon of claim 23 wherein the object is a ball.

25. The gas cannon of claim 23 wherein the piston comprises:

first and second pistons being coupled together by a coupling member and being disposed within the bore of the structure for longitudinal movement therein, the second piston having the contour shaped to cradle the object when the object is propelled from the bore; and

a baffle comprising an outer surface which fixedly engages the surface of the bore of the structure at a predetermined location to divide the bore into two parts, the baffle defining an aperture through which the coupling member is able to move when the first and second pistons are caused to move by the accelerating/decelerating means.

26. The gas cannon of claim 25 wherein:

the structure defines at least one aperture through one of the sidewalls of the structure, and the bore has a shape selected to house the object therein prior to the object being propelled therefrom; and

the decelerating means operates to decelerate the piston when the first piston passes the at least one aperture so as to cause gas trapped between the first piston and the baffle to be compressed and to limit further movement of the piston means.

27. A gas cannon for propelling an object placed therein comprising:

a tube having sidewalls which define a longitudinal bore, and an inlet port at a first end of the tube for selectively receiving a gas into the bore, the size of the bore being selected so as to allow the object to be placed therein;

first and second pistons being coupled together by a coupling member and being disposed within the bore of the tube for longitudinal movement with the first piston being located closer to the inlet port than the second piston, the second piston comprising a major surface for cradling the object such that when the object is propelled from the bore the object does not touch the sides of the bore;

a baffle comprising an outer surface which fixedly engages the surface of the bore of the tube at a predetermined location to divide the bore into two parts, the baffle defining an aperture through which the coupling member is able to move when the first piston is caused to move by the gas entering the inlet port of the tube.

28. The gas cannon of claim 27 wherein the tube has at least one aperture formed through a sidewall thereof, the at least one aperture being located so as to facilitate the escape of any gas in the bore of the tube between the baffle and the first piston while the first piston is located between the inlet port and the at least one aperture, and for facilitating the escape of gas introduced into the inlet port when the first piston is between the at least one aperture and the baffle.