next , fig1 through 7 are used to explain a putter club 10 which is an embodiment of the present invention . the same symbols are used for portions identical to those in fig8 and 9 and details thereof are omitted here . fig1 is a side view of the putter club 10 at the time of putting , like fig8 . fig2 is a detail of principal elements at the time of impact . like the conventional putter club 1 ( fig8 ), the putter club 10 comprises at least a shaft 2 , a putter head 3 , and a grip 4 ; the center of rotation p is congruent to the grip area 6 on the grip 4 . specifically , if a person is right handed , the grip area 6 is the portion held by the thumb of the left hand overlapped by the palm of the right hand . the center of rotation p of the putter club 10 during putting is located on this grip area 6 . with a putter club 10 having such a structure , a force , causing the putter club 1 to rotate clockwise in the figure around the center of rotation p , acts on the hands of a golfer putting with a hold on the grip area 6 and putting , as shown in fig1 and 2 . however , because the golfer is holding the center of rotation itself , the reaction force a of the grip end 8 is lower and the reaction from the golf ball 5 on the hands 7 of the golfer is less than in the conventional case shown in fig8 . consequently , the direction and force , operating in the putting direction and at the power visualized by the golfer , can be transmitted correctly from the golfer &# 39 ; s hands 7 to the putter club 10 . appropriate putting can thereby be performed . the method for adjusting the center of rotation p and calculating its position are explained on the basis of fig3 and 4 . fig3 is a side view showing an exploded view of the elements of the putter club 10 . the putter club 10 comprises a shaft 2 , putter head 3 , and grip 4 , as well as auxiliary weights ( head side auxiliary weight 11 and grip side auxiliary weight 12 ) which can be mounted within the shaft 2 . the head side auxiliary weight 11 and grip side auxiliary weight 12 may both be mounted or either one may be mounted alone . moreover , the constitution of the shaft 2 is arbitrary and , for example , may comprise a tip portion 13 mounted on the putter head , a pad portion 14 mounted on the grip 4 , and a tapered portion 15 therebetween . l1 represents the distance from the center of gravity q of the putter club 10 to the center of rotation p . as shown in equation ( 1 ) in fig4 this distance l1 can be attained from the moment of inertia i of the putter club 10 around the center of gravity q , the mass m of the putter club 10 , and the distance l2 from the putter head 3 to the center of gravity q . as shown in equation ( 2 ), the moment of inertia i can be attained from the mass m i of the elements constituting the putter club 10 , the distance d i from the grip end 8 to the elements with this mass m i , the mass m of the putter club 10 , and the distance g from the grip end 8 of the putter club 10 to the center of gravity q . as shown in equation ( 3 ), the distance g from the grip end 8 to the center of gravity q can be attained from the mass m i of the elements constituting the putter club 10 , the distance d i , from the grip end 8 to the elements with this mass m i , and the mass m of the putter club 10 . consequently , as shown in equation ( 4 ), the distance l3 from the grip end 8 of the grip 4 to the center of rotation p can be attained from the length z of the entire putter club 10 , the distance l1 from the center of gravity q to the center of rotation p , and the distance l2 from the putter end 3 to the center of gravity q . the distance l1 from the center of gravity q to the center of rotation p and the distance l3 from the grip end 8 to the center of rotation p are functions of the distance or length and the position and mass of each element of the putter club 10 . the mass distribution is adjusted by appropriate selection of these elements and the center of rotation p can thereby be made congruent to the position of the grip area 6 . the many elements constituting the putter club 10 include a shaft 2 , putter head 3 , grip 4 , head side auxiliary weight 11 , grip side auxiliary weight 12 . it is therefore practical to make an appropriate selection of the position , mass , and length of the head side auxiliary weight 11 and grip side auxiliary weight 12 , and make adjustments thereto using a simulation . the head side auxiliary weight 11 and grip side auxiliary weight 12 are generally mounted within the shaft 2 , but can also be mounted on the outer surface thereof . naturally the head side auxiliary weight 11 and grip side auxiliary weight 12 can be selected to suit variations of the shaft 2 , putter head 3 , and grip 4 . the mass distribution of the entire putter can be varied by the choice of the thickness of each portion ( tip portion 13 , pad portion 14 , and tapered portion 15 ) of the shaft 2 or the thickness of the grip 4 . the center of rotation p can also be adjusted to a position on part of the grip 4 . for example , the mass distribution can be adjusted by making the tip portion 13 on the putter head side 3 of the shaft 2 relatively thin while making the pad portion 14 on the grip 4 relatively thick . furthermore , an auxiliary weight ( not shown ) may also be mounted on the grip end 8 of the grip 4 . moreover , these auxiliary weights , including the head side auxiliary weight 11 and grip side auxiliary weight 12 , may be made of any material , but lead or other material with a comparatively large specific gravity is preferable . fig5 is a side view of a putter club 10 showing an example of the case where the center of rotation p is adjusted to the grip area 6 in this manner . the distance l1 from the center of gravity q to the center of rotation p is preferably 4 / 10 to 6 / 10 ( 1 / 2 , for example ) of the total length of the putter club 10 . it is thereby possible to give the putter good balance and an easy swing . according to a golfer &# 39 ; s requirements , the space between this center of rotation p and grip area 6 can be varied slightly to make a sensitive putter club 10 . in this case , the length between the grip area 6 and the center of gravity q is preferably 4 / 10 to 6 / 10 ( 1 / 2 , for example ) the length z of the whole . fig6 is a graph ( graph showing the relationship between the shock and the distance from the grip end 8 ) of the shock during putting with the center of rotation p at various positions in the grip 4 . it was found that the shock from the golf ball during putting was minimized at a given position ( center of rotation p ) on the grip 4 . in other words , the reaction from the golf ball 5 due to the impact is transmitted through the putter club 10 and returns from the grip area 6 to the hands 7 of the putting golfer . this sensation is of only the force of the putting action and does not include any sense of force wasted in suppressing the reaction ( in effect , without requiring the operation of suppressing the reaction as shown in fig8 and 9 ). this gives the golfer a sense of putting more correctly and as visualized . the movement of the center of rotation p to the grip area 6 in the grip 4 in this manner optimizes the sweet spot axially with respect to the putter club 10 . even if the point of impact of the putter head 3 during putting is slightly shifted in an axial direction , the operating force can be transmitted correctly ; and the sweet spot is thereby more expansive than in conventional putters . specifically , fig7 is a figure showing the expansion of the sweet spot s on the impact surface of the putter head 3 due to the movement of the center of rotation p from the shaft 2 to the grip 4 . when the center of rotation p is on the shaft 2 as in conventional examples ( fig8 ) , the angle θ1 formed by the spread of the sweet spot s is greater than the angle θ2 formed by the spread of the sweet spot s when the center of rotation p is on the grip area 6 . consequently , if the angle θ1 from the center of rotation p on the grip area 6 is drawn to the impact surface of the putter head 3 , it covers a wider area than the angle θ2 and can enlarge the sweet spot s on the impact surface of the putter head 3 . in this way , the sweet spot s , enabling appropriate and correct putting , can be enlarged in both the axial direction of the putter club 10 and on the impact surface of the putter head 3 . more sensitive putting can thereby be realized . moreover , various adjustments to the center of rotation p on the grip 4 can make the putter club 10 more sensitive to the characteristics and habits of a golfer . the present invention as discussed above can realize more correct and appropriate putting because the center of rotation of the putter club during putting is located on the grip . this reduces unintentional movement of the entire putter club because of reaction to the hands from the golf ball and can transmit the putting force effectively to the golf ball . in other words , the sweet spot of the putter head and the sweet spot in the lengthwise direction of the putter club can be made to match correctly with the center of the hands ; also , the reaction force applied to the hands by the shock during putting is minimized . a golfer thereby gets correct feedback to his / her visualization of the putt and the energy of the putting action can be transmitted with maximum efficiency .
the present invention provides a putter club 10 which minimizes the reaction from the golf ball 5 during putting , effectively and appropriately transmits the putting force to the golf ball 5 , and provides an effective sense of putting distance . the present invention is characterized by the location of the center of rotation p of the putter club 10 during putting at a position on the grip 4 , by this arrangement minimizing the reaction from the putter club to the hands , and by the location of the center of rotation p of the shaft 2 during putting on the grip 4 , making it easy to control the entire putter club .