GB2351451A - A method for analysing a golfer's swing - Google Patents

Abstract

A method of analysing a golfer's swing of a golf club 13 with a force sensor 14 comprises the steps of providing a recording device 20 to sense and record data relating to the swing, measuring at least one force acting on said club using the sensor, detecting the occurrence of a preselected event using said measured force, determining a trigger point on said event and then triggering the recording device. The forces measured may be the torsion or the flexing of the club shaft and may also be recorded at the trigger point. Preferably the recording device comprises a film or digital camera 20 and a strobe 22.

Description

2351451 Golf Swing Analysis Method This invention relates to a method for

use in analysing the dynamics of a person's golf swing for the purpose of improving the swing.

Various techniques exist for teaChing golf, including personal instruction by a golf professional, written instruction in the form of books and magazine articles, and, more recently, video instruction. Recent electronic advances have made possible different video systems, mechanical trainers, and club head analysers to determine club head.path and velocity. Weight distribution systems that analyse weight shift in combination with video systems are also available. There also exists image freeze systems that are used to compare a golfer's head, back, and arm positions with those of professionals.

It is well known that, when a golfer swings a golf club, the shaft will flex due to forces acting on the club head. Electronic sensors, such as strain gauges have been used by golf club manufacturers for measuring flexures of shafts formed from various materials, determining stress levels to prevent shaft overload, and determining optimal shaft stiffness.

Shaft flexing is due to a number of dynamic forces resulting from the swinging of a golf club. For example, in those instances in which the club shaft is fitted to the club head adjacent the heel, swinging if the club causes the toe of the head to droop due to centrifugal force, thereby imposing on the shaft a flexing force tending to arch the shaft in a plane perpendicular to the path of the club during the swing. The shaft is also arched longitudinally in the plane of the swing path due to the lag of the club head during the swing. In addition, swinging of the club causes the club head to.impose-a torsional force on the shaft.

2 All of these forces vary to some extent during the swinging of the club and the variations may be due to any one or more of a number of factors. For example, changes in acceleration will cause the longitudinal arching and twisting of the shaft to vary during a continuous swing. In addition, the forces imposed on a club -shaft may vary depending on whether the path of the club head as it approaches a ball is what is known as inside out, outside in, or directly toward the target.

Currently available teaching systems generally relate to a person's body position, the club head path, swing speed, timing, and other attributes of a golfer's swing. However, what is needed is a system that can be used to identify and record significant events that occur at selected time periods during the course golf swing so as to enable the person to understand what occurs during the swing and undertake training to improve the swing.

According to the invention there is provided a method of analysing a golfer's swing of a golf club having a sensor capable of measuring a force acting on said golf club during the golfer's swing of said golf club along a path, said method comprising the steps of- providing a recording device orientated relative to the path to sense and record data relating to the golfer's swing; measuring at least one force acting on said golf club during the golfer's swing using said sensor; detecting the occurrence of a preselected event using said measured force; determining at least one trigger point on said preselected event; and triggering said recording device at said trigger point to acquire instantaneous data relating to the golfer's swing at least one-position of -Said golf club along said path-.' A preferred embodiment of the invention is illustrated in the accompanying drawings n 1 C_ 3 wherein:

Figure 1 is a block diagram of the golf swing analyser; Figure 2 depicts the analysing methodology using the apparatus of Figure 1; Figure 3 is a side elevational view of a golf club used with the apparatus of Figure 1 showing the placement of the sensors; Figure 3A is an enlarged, fragmentary, side elevational view of a section of the shaft of the golf club of figure 3 showing the placement and orientation of sensors for detecting flexing of the shaft in one direction transversely of the longitudal axis thereof; Figure 4 is a front elevational view of the golf club of Figure 1; Figure 4A is an enlarged, fragmentary, front elevational view of a section of the shaft of the golf club of Figure 3 showing the placement and orientation of sensors for detecting flexing g of the longitudinal axis thereof, Figure 4B is an enlarged, fragmentary, front elevational view of another section of the shaft of the golf club of Figure 3 showing the placement and orientation of torsion detecting sensors; Figure 5 is a cross-sectional view taken along the line 5-5 of Figure 4 showing the various axes along which strain within the golf club shaft is measured; Figure 6 is a schematic diagram of a full-bridge circuit used in the apparatus of Figure 1 to generate Vh, Vv, and Vt signals for transmission to and processing by the computer of Figure 1; Figure 7 is a schematic diagram of another embodiment of a bridge circuit which can be used with the apparatus of Figure 1; and Figure 8 depicts exemplary graphs of the data acquired by the computer from the 4 sensors on the golf club shaft.

A golf swing analyser 9 according to the invention includes a golf club 10 having an elongate shaft 11 at one end of which is a club head 12 and at the opposite end of which is a grip 13. A plurality of sensors 14 capable of detecting flexing and torsional features are fixed on the shaft 11 and wired together into a bridge circuit 16 that provides analog data signals to computer 18 for processing and controlling a camera: 20 and strobe 22. Sensors 14 are used to provide data to computer 18 indicative of the flexing (bending) and torsion (twisting) of the shaft 11 of golf club 10, as will be described in greater detail below. The magnitude of flexure along a pair of orthogonally-related axes is measured and represented by two analog voltage signals, Vh and Vv. The magnitude of torsion of the shaft is measured and represented by a third analog voltage signal, Vt. These signals are delivered to and digitized by computer 18 using a conventional A/D converter 24. The resulting data can be processed for various purposes, including providing a graphical or numerical printout or display of the data or controlling the operAtion of camera 20 and strobe 22 to photograph the golfer at one or more instants during the swing.

One example of the use of the acquired data is illustrate in Figure 2. In this example, the golf swinger analyser 9 is used to detect a preselected significant event that occurs during 0 the course of a golf swing and to trigger the camera and strobe to photograph the golfer, either 0 at the instant that event occurs or at a preselected later point in the swing. Thus, the first step is to use computer 18 to acquire the data generated by sensors 14 over the course of the golf swing, as indicated at block 3 0. That data then is analysed by computer 10 which uses pre- programmed criteria to determine or select in real time a particular event that occurs during the course of the swing. This is indicated at block 32. Using this information, computer 18 determines one or more trigger points, as shown by block 34. Each trigger point can be concurrent with the particular event or delayed to anti6ipate a later event that is to be captured by the photograph. The camera and strobe are then activated at the trigger point to capture a photograph of the golfer at a specific point in the swing, as indicated at block 36.

The golf club 10 as shown in Figures 3 and 4 is fitted with three sets of sensors 14 fixed on the shaft I I in such manner as to generate the Vh, Vv, and Vt electrical signals. The first set of sensors includes two pairs of flexure sensors Hl. H2, H3 and H4. The second set includes two pairs of torsion sensors TI, T2, T3, and T4. The horizontal sensors are so named because they measure flexure which occurs transversely of the longitudal axis 15 and of the shaft and lies along the path or plane along which the golf club travels during the golfer's swing. The vertical sensors are so named because they measure flexure which occurs transversely of the longitudal axis 15 and perpendicular to the path of the swing, or 90' removed from the other transverse flexure. The torsion sensors are so named because they measure twisting of the shaft about its axis 15. In figure 5, therefore, the axis labelled H indicates the horizontal flexure, the axis labelled V indicates the vertical flexure, and the curve labelled T indicates the directiofi of torsion that is sensed.

The horizontal, vertical, and torsion sensors can all be strain gauges of known kind that have a resistance which varies with the amount of flexure undergone by the substrate or other surface to which they are attached. The sensors are attached to the surface of shaft 11 of golf club 10 using an adhesive that permits any flexure -or torsion of shaft I I to be transmitted to the sensors. Sensor designated ADXL05 manufactured Analog Devices are suitable for I I C' 6 use. Although strain gauges are described as constituting the sensors, it will be understood that accelerometers, variable resistors, and other suitable sensors can be used in lieu of strain gauges.

For the horizontal and vertical sensors, the circumferental position and orientation of each sensor is selected so that the sensor responds only to strain along its associated axis. As shown in Figures 3A and 4A, the pairs of horizontal sensors are mounted at diametrally opposed locations along the horizontal axis H shown in Figure 5.

These sensors are oriented so that they extend axially along shaft 11. The sensors of one pair (sensors H1 and H3) are spaced 180' apart about the circumference of shaft I I from the sensors of the other pair (sensors H2 and H4). In this way, flexure of shaft 11 along the plane of the swing path will cause one pair of horizontal sensors to be subjected to compression forces and the other pair to be subjected to tension forces. As will be described below, the resulting changes in resistance of the horizontal sensors are used to generate the analog voltage Vh.

As also is shown in Figures 3A and 4A, the pairs of vertical sensors are mounted at diametrally opposed locations along the vertical axis V depicted in Figure 5. Thus, these vertical sensors are spaced 90' from the horizontal sensors. The vertical sensors are oriented so that they extend axially along shaft 11. As with the horizontal sensors, one pair of vertical sensors, V1 and V3, is spaced 180' about the circumference of shaft I I from the other pair of vertical sensors, V2 and V4. As a result, flexure of shaft I I in a direction normal to the swing path will cause one pair of vertical sensors to be subjected to compression forces and the other to tension forces, thereby resulting in changes in resistance of the sensors that are used 7 to generate the analog voltage Vv.

As shown in figure 4B, the torsion sensors T 1 -T4 are oriented at a 45' angle with respect to longitudinal axis 15 of the golf club. The sensors of one pair of sensors, T2 and T4, are at the same axial position on the shaft and the sensors TI and T3 of the other pair are diametrally opposed to the first pair. The sensors of each.pair are oriented at a 90" angle with respect to each other; sensor T I has the same orientation as sensor T2, while sensor T3 has the same orientation as sensor T4.

The effect of orientation of the torsion sensors can be understood by inspection of the bridge circuit 16 shown in Figure 6. Circuit 16 actually comprises three full bridges, one for each set of sensors. The torsion bridge utilises sensors T1 and T2 to form one voltage divider extending between a supply voltage and common ground. Sensors T3 and T4 form a second voltage divider connected in parallel with the first. The analog voltage Vt is the differential voltage between the centre points of the voltage dividers. As will be understood by inspection of Figures 4B and 6, flexure of shaft 11 along the plane of the swing path (i.e. Along the horizontal axis) will have the same effect on all four torsion sensors; all will be in compression or all will be in tension. Thus, the ratio of resistance value of sensor TI to sensor T2 will be the same as that of sensor T3 to sensor T4 and voltage Vt will therefore be zero. Flexure of shaft I I in the vertical direction will result in the resistance of sensors T I and T3 changing an equal amount and also will result in the resistance of sensors T2 and T4 changing an equal amount. Thus, voltage Vt will remain unchanged by this type of flexure. Accordingly, given the orientation of the torsion sensors and their connection in the fall bridge shown in Figure 6, flexure of shaft 11 in any direction will have no effect on voltage Vt. Rather, voltage Vt will have a magnitude (positive or negative) only in the event of 8 twisting shaft 11, since torsion will place sensors TI and T4 in the same state as each other (either tension or compression) and will place sensors T2 and T3 in the other state. For the horizontal and vertical sensors, the connection of those sensors in full bridges is done in a manner similar to that used for the torsion sensors, except that the positions in the bridges of sensors H3 and H4, as well as sensors V3.and V4, must be switched.

With continued reference to Figure 6, it will be understood that the wiring of sensors 14 in the bridge circuits can be done on the shaft 11 of the golf club itself The only external connections necessary are those required to supply the input voltage Vf and to conduct the output voltages Vii, Vv, and Vt. These connections can be hardwired as shown in Figure 1 or, if the golf club is fitted with a battery or other source of power, then wireless transmission of the output voltages can be achieved.

In addition to placing the sensors in a preselected axial orientation and circumferential position, it i desirable to determine the optimum location along the lengt h of shaft 11 for placement of each set of sensors. Because the shaft of a conventional golf club does not have a uniform diameter and wall thickness along its length, the amount of bending of the shaft during a swing will vary between the grip and club head. Since the magnitude of the signal provided by the horizontal and vertical sensors is a function of the degree of bending of the shaft during the swing, the magnitude of the signals provided by these sensors can be maximised by locating the sensors at the point along the length of the shaft that undergoes 0 maximum bending during the swing.

This ideal placement can be determined by finding the location L along the length of the shaft at which the result of equation (1) is maximised:

1 (7, 9 (1) where: r' equals the outside diameter of the shaft; ri equals the inside diameter of the shaft; and K equals a constant.

Similarly, the ideal placement of the torsion sensors is that position along the length of the shaft at which the maximum amount of twisting occurs. That position can be determined by finding the location at which the result of equation (2) is maximised:

(2) It should be noted that, if necessary or desired, the sensors can be located at other positions along the length of the shaft, the only requirement being that the selected location is such that the sensors will provide a signal of sufficient magnitude that the desired trigger points can be determined.

Although the illustrated embodiment shows four sensors being used for the measurements of strain in different directions, it will be understood that more or fewer sensors could be used. For example, two sensors could be used and connected into a half bridge circuit, as shown in Figure 7. However, this arrangement is not preferred since the magnitude of the resulting analog output signal will be only half of that generated by the full bridge circuits of figure 6.

The operation of camera 20 and strobe 22 shown in Figure 1 can be implemented in a 0 variety of ways. If there is low ambient light, the camera shutter can be opened prior to the trigger point and the strobe can be used to provide instantaneous illumination at the trigger point. The camera shutter can thereafter be closed. Alternatively, camera 20 can have its own flash or can be wired to strobe 22 op some other flash so that the flash is activated by virtue of the camera's being activated, rather than by a separate output from computer 18. Camera 20 can be a standard film camera or a digital camera, in which case the digital image data conveniently can be stored and later recalled for display, printing, or other use. If multiple trigger points are desired, several cameras can be used to capture two or more events during the course of a single golf swing. Preferably, the trigger points are recorded and stored along with the acquired sensor data so that the photographed image can be correlated with the sensor data.

As mentioned above, computer 18 analyses the acquired sensor data to locate a particular event and then activates the camera and strobe to photograph the golfer's position either at that instant of time or at a later time during the swing. Figwe 8 shows three graphs illustrating exemplary strain profiles in the vertical, horizontal, and torsion directions. In this example, four photographs are taken during the time of the swing, as indicated by numbers 1-4. The first of these corresponds roughly to the early part of the swing when the golfer's arms are in the nine o' clock position. This point can be determined by computer 18 by analysing the vertical strain (Vv) and triggering when that signal reaches a negative peak. The 0 tp second point is at the time of impact between the club head and ball and this point can be determined by monitoring the horizontal strain (Vh) for a zero crossing in the positive direction. The third point is after impact and corresponds roughly to the golfer's arms being in the three o' clock position. This point can be triggered by waiting 70ms after impact. The 4 fourth point is the finish of the swing and can be determined by monitoring one or more of the analog signals to determine when it returns to zero or plateaus near zero.

Computer processing of the sensor data can include O'P'eratio ns.-other than determination or selection of particular events and trigger points. For example, the received sensor data can be filtered to smooth the signal or analysed to determine the appropriate type of club construction (e.g, metal or graphite shaft) or swing weight for the golfer.

The golf swing analyser of Figure 1 can include additional sensors that provide an output which can be processed by the computer to determine a desired trigger point. For example, strain gauges, load cells, or other suitable sensors could be located beneath the golfer's feet and used by the computer to measure weight shift.

This disclosure is representative of the presently preferred embodiment of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.

Claims (7)

12 Claims: 1. A method of analysing a golfer's swing of a golf club having

a sensor capable of measuring a force acting on said golf club during the golfer's swing of said golf club along a path, said method comprising the steps ofiproviding a recording device orientated relative to the path to sense and record data relating to the golfer's swing; measuring at least one force acting on said golf club during the golfer's swing using said sensor; detecting the occurrence of a preselected event using said measured force; determining at least one trigger point on said preselected event; and tri a ering said recording device at said trigger point to acquire instantaneous data

Z19 relating to the golfer's swing at least one position of said golf club along said path.

2. The method according to Claim 1 wherein the measuring step comprises measuring the torsion of said shaft during the golfer's swing.

3. The method according to Claim 1 or 2 wherein the measuring step comprises measuring flexing of said shaft during the golfer's swing.

4. The method according to Claim 1, 2, or 3 flirther recording said measured force at least at said one trigger point.

5. The method according to any of Claims 1 to 4 wherein said recording device comprises a film camera.

6. The method according to any of Claims 1 to 5 wherein said recording device flirther comprises a strobe and wherein said triggering step further comprises triggering said strobe at said one trigger point.

7. The method according to any of Claims 1 to 6 wherein said recording device comprises a digital camera.