The present invention relates to the field of monitoring and analyzing skiing activities, and specifically: to monitor the skier body position and forces experienced by his/her body and equipment; to provide new level of safety; and to enhance skiing experience. Such system is based on processing sample data from various MEMS (Micro-Electromechanical System) sensors embedded in the ski equipment and/or skier clothing then calculating moments applied to various parts of the user body and his equipment and to provide corrective feedback to the actuators embedded in the ski equipment. Among other, such corrective action may consist of: changing the tension (extend or shorten) of the ski edge to aid in edge handling; change the torsion of a selected parts of the ski; damping vibration of the ski; and release of the ski bindings when moments applied to the skier leg exceeds safety limits.
Currently monitoring of skier/skiing performance relies on few techniques, such as: skier feelings, instructor/coach observations, etc, and some empirical factors, such as: time measurements, post run video analysis, while the safety and comfort depends on decades old ski binding technology, incremental progress in materials and manufacturing technology.
Some analytical methods for data collection during the development phase of the ski equipment are in use today, however, most of those techniques are not practical for the every day training of professional or recreational skier, as they require bulky equipment and require large team of highly skilled technicians to operate.
It is well known that the safety of skiing depends predominantly on ski bindings. Currently, binding safety is defined by the stiffness of it's spring(s) used to hold/release ski boot, which is adjusted according to the presumed capability of the user and the user weight. This basic principle of ski binding didn't changed in past 40 years (also many incremental improvements, such as: multi-pivots/springs were added), and perform satisfactory most of the time—when the speeds are modest, the spring pre-set torque was below the critical level and the user is physically fit, the fundamental problem—relying on intuition for setting the spring strength and fact that in almost all cases, only one of the binding, the one experiencing excessive force, will release. This is mainly to the fact that the forces applied to both skis and/or skis trajectory are not the same. In effect, while one ski is released the other, the other is still attached to the user causing serious injuries during a fall.
The comfort and safety of skiing is also affected by excessive ski vibration. Such vibrations are an effect of the moments applied to the ski edge by skier body position in relation to ski slope when the ski turns, especially on a hard icy snow or moguls. Since part of skiing experience is related to turns, manufacturers introduced skis with strong sideline curvature—broader tip and tail and narrow center, and high flexibility. Unfortunately, such design leads to large vibration amplitudes, so skis are manufactured with different stiffness factor to balance the needs and experience of broad range of skiing enthusiasts, from beginners to professionals. In effect, soft and highly flexible skis, targeting average expertise levels and/or soft snow have tendencies to vibrate excessively at high speeds or in tight turns or hard or icy snow, while less flexible or stiffer skis, targeted for experts are difficult to control by an average skilled user. However, all skis, regardless of their design parameters will vibrate in turns does loosing the edge contact with the snow making edge control difficult and increases discomfort and decreases safety and performance.
Depending on the speed and snow condition, ski vibrates at several bending and torsional frequencies with the amplitudes of such vibration dependent on ski construction—stiff and hard ski may have lower amplitudes at some frequencies but are difficult to control by an average user, while soft ski may be easy to control but have higher vibration amplitudes. In general, the ski bending frequencies are between 10 Hz and 100 Hz, while the torsional frequencies are in the range of 100 Hz to 150 Hz.
For several decades designers try different materials, manufacturing techniques and vibration damping schemes to somehow minimize its negative effect. As the ski vibrates predominantly at the front and the tail quarters of its length, various damping materials and structures were added to the front, tip and tail of the ski.
However, adding large amount of damping does not solve this problem while making ski less responsive and slow. It is well know that ski vibrates over relatively wide range of frequencies, and while dampening materials or dampening viscous structures are effective to damp particular frequency, such structures are not efficient in damping wide range of frequencies, and sometime even counterproductive. Ceramic piezoelectric structures were proposed to provide active dampeners, however, since only small amount of strain—as low as 1%, is usable to provide the control signal, they proved to be difficult to control and unstable or require “pre-tension” of the piezoelectric material in proportion to the expected bending forces in order to produce reference signal, and as such not compatible with ski manufacturing technologies.
As the current monitoring systems are not practical for every day use, not only the analysis of the skier run is relegate to post run subjective interpretation, but more significantly the safety of the skier (such as the response of the ski bindings) is left virtually unchanged for the past thirty years, thus also the number of recreational skiers increased, their safety and experience is not improved.
In recent years, the use of mobile devices and, in particular, cellular telephones has proliferated. Today, cellular phone besides providing basic communication over cellular network is equipped with various input/output capabilities, such as wireless PAN (Personal Area Network), and provides significant computing resources. When such computing resources communicate with the remote sensors, such as MEMS accelerometers, magnetometers, gyroscopes, pressure sensors, actuators the resulting system can provide various sport analytical tools for monitoring of v skiing.
By coupling MEMS accelerometers and actuators embedded in the ski equipment with an analysis application residing in the user smart-phone, one can provide tool analyzing forces experienced by the user and increase in safety and comfort of skiing. Furthermore, using the smart-phone connectivity to the wireless cellular network, a real-time feedback to the remote location may be provided to add in ski testing or training. System described in this invention can operate using any of wireless technology such as: cdma2000, UMTS, WiMax, LTE. LTE-A, etc.
This invention allows for the analysis of skiing and remote monitoring of the skier performance. The system consists of a various sensors embedded in the ski equipment or attached to the skier, communicating wirelessly with analysis application residing in the skier smart-phone. The output of the sensors representing instantaneous changes in acceleration in X/Y/Z axis, and in relation to the changes in earth magnetic field provide data for calculation of skier position, moments applied to the ski edges, and forces experiences by the skier body and his equipment.
When augmented with video capture, GPS supported ski slope mapping system, or radio telemetry or GPS synchronized CCTV systems installed along the ski slope, or barometric pressure capability, such sensory system when integrated with wireless cellular network (Wireless Metropolitan Access Network). After analysis, such data may be presented
According to this invention the MEMS motion sensors such as: accelerometers, gyroscopes, magnetometers, barometric pressure and MEMS actuators are embedded in various locations essential for the measurement of skier performance, such as: skis, ski boots, cloth, poles, gloves, etc. Those sensors are sampled at an appropriate rate to provide real-time measurements of moments applied to the ski equipment and skier body.
When such sensors are equipped with the wireless communication link and monitoring application capable of analyzing such data, such system can provide real-time monitoring of skier performance. The results of such analysis can be transmitted over-the-air using mobile terminal wireless interface or can be stored in the mobile terminal memory, then downloaded into computer for further analysis.
When such system is equipped with the graphic rendering and capable of retrieving topological information from a radio-telemetry, GPS or GPS synchronized video from slope installed CCTV cameras, such system can display skier position in relation to the slope does allowing for the real-time analysis (by the coach) or post-run review by the user. Both the real-time and post-run analysis provide recording of all parameters of the run, such as edge forces, acceleration, etc, as well as rendering of skier position vs. slope. Furthermore, the graphical representation of the run can be interpolated between the samples to provide a visual representation of the entire run.
It is well known that ski or snowboard turns when moments are applied to the ski edge by skier body position in relation to ski slope and the skier speed, and the turning performance is determined by the centrifugal force and the reaction to this force introduced by ski-snow contact.
To achieve tight turning radius, the ski sideline edge is curved and ski is made flexible to allow bending during the turn and avoid rolling. To improve the experience of skiing, manufacturers introduced skis with strong sideline curvature—broader tip and tail and narrow center, and high flexibility. In effect, highly flexible skis have tendencies to vibrate excessively at high speeds or in tight turns or hard or icy snow. When ski vibrates, it looses the edge contact with snow making edge control difficult, decreasing comfort, safety and performance.
It is also well known that skiing safety is very much related to skier skills, it is well understood that ultimate safety is proportional to many factors even beyond control of professional skiers. However, the only part of ski equipment dedicated to safety and fundamentally unchanged during almost half century, is a ski binding, still relying on an arbitrary setting of binding spring tension. In most cases, binding settings is related to the user weight and inferred skills, and not to dynamic condition during the ski run.
MEMS accelerometer/actuator subsystem can be delayed as a safety device in the ski bindings for the purpose of instantaneous release of the ski, when moments experienced by the skier body, ski or ski binding exceeds dynamic parameters determined to be safe by providing a real-time feedback to the MEMS actuator(s) embedded in the ski bindings. Such safety system can be integrated into ski equipment and controlled in a real-time by the feedback mechanism provided by the monitoring application, does providing an additional protection to the user.
System residing in the skier smart-phone and communicating is equipped MEMS sensors and actuators embedded in various position of the ski equipment and performing real-time of forces experienced by the equipment and the skier body may provide visual analysis of run, compensate and correct errors, damp ski vibration to improve comfort and release ski bindings for improved safety.
A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description therefore are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
The following is a glossary of terms used in the present application:
Active Monitoring System—in the context of this invention a system able to collect various instantaneous vectors such as, acceleration, angular orientation, geo-location and orientation, then using various angulation and mathematical operations calculate the forces applied to various areas of sport equipment or the user body then send commands to actuators embedded in the sport equipment to provide corrective action.
Application—the term “application” is intended to have the full breadth of its ordinary meaning. The term “application” includes 1) a software program which may be stored in a memory and is executable by a processor or 2) a hardware configuration program useable for configuring a programmable hardware element.
Coach—in the context of this invention, any person authorized by the user to receive the data from the user monitoring system and provides analysis in real-time or off-line of the user performance.
Computer System—any of various types of computing or processing systems, including mobile terminal, personal computer system (PC), mainframe computer system, workstation, network appliance, Internet appliance, personal digital assistant (PDA), television system, grid computing system, or other device or combinations of devices. In general, the term “computer system” can be broadly defined to encompass any device (or combination of devices) having at least one processor that executes instructions from a memory medium.
Mobile Terminal—in the scope of this invention any wireless MAN enabled terminal such as cell-phone, smart-phone, etc.
Memory Medium—Any of various types of memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a CD-ROM, floppy disks 104, or tape device; a computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, etc.; or a non-volatile memory such as a magnetic media, e.g., a hard drive, or optical storage. The memory medium may comprise other types of memory as well, or combinations thereof. In addition, the memory medium may be located in a first processor in which the programs are executed, or may be located in a second different processor which connects to the first processor over a network, such as wireless PAN or WMAN network or the Internet. In the latter instance, the second processor may provide program instructions to the first processor for execution. The term “memory medium” may include two or more memory mediums which may reside in different locations, e.g., in different processors that are connected over a network.
NFC—in the scope of this invention a type of radio interface for near communication.
PAN—in the scope of this invention, a personal are network radio interface such as: Bluetooth, ZigBee, Body Area Network, etc.
Passive Monitoring System—in the scope of this invention a system able to collect various instantaneous vectors such as, acceleration, angular orientation, geo-location and orientation, then using various angulation and mathematical operations calculate the forces applied to various areas of sport equipment or the user body to provide on-line or off-line analysis of the user performance.
QR-code—Quick Response Code, a 2-D bar code
Ski Equipment—in the context of this invention, any part of equipment used by the skier, such as: skis, ski boots, ski poles, ski clothing, ski glows, etc.
Ski Equipment Parameters—in the context of this invention, ski or snowboard design and manufacturing parameters, such as: length, weight, toe/center/tail, stiffness, are extracted after manufacturing and entered into application.
Software Program—the term “software program” is intended to have the full breadth of its ordinary meaning, and includes any type of program instructions, code, script and/or data, or combinations thereof, that may be stored in a memory medium and executed by a processor. Exemplary software programs include programs written in text-based programming languages, such as C, C++, Visual C, Java, assembly language, etc.; graphical programs (programs written in graphical programming languages); assembly language programs; programs that have been compiled to machine language; scripts; and other types of executable software. A software program may comprise two or more software programs that interoperate in some manner.
Topological Information—in the context of this invention, information about the topology of the ski slop obtained through any combination of techniques such as: topography maps, GPS, Radio-Telemetry, barometric pressure monitoring, etc.
User—in the context of this invention, skier using the monitoring system.
Vibration Control System—in the context of this invention a system able to collect various instantaneous vectors such as, acceleration, angular orientation, etc., then using various mathematical operations calculates resonance frequencies of vibrating ski then sends commands to actuators embedded in the sport equipment to provide corrective action.
WMAN—Wireless Metropolitan Access Network such as cellular network.
The proposed method leverages on the properties of wireless Personal Area Network (PAN) such as Bluetooth and wireless wide area network, such as a cellular network, and combines the inherent benefits provided by those networks with the sensing technology such as: MEMS accelerometers, gyroscopes, magnetometers, actuators, embedded into skier equipment and an application software residing in the personal wireless terminal (for example user cell-phone).
In this invention sensor technology embedded in various places of the user ski equipment, provides instantaneous measurements of various moments applied to the skier body and his equipment to a mobile terminal based monitoring application over the PAN wireless interface. These measurements in addition to topological and location information (obtained from preloaded slope maps, GPS, Galileo, radio-telemetry, etc.), as well as user physical parameters, such as: weight, heights, distance from ankle to knee and hip, etc, and ski physical parameters, such as: total length, edge length and radius, etc. are used by the monitoring application to provide piece-wise analysis of the user run.
Since the ski edging is created by tipping (inclining) different parts of the skier body: feet/ankles, lover legs/knees, upper legs/hips and lower spine, then by placing sensors in various positions of ski equipment and skier body and then continuously recording the instantaneous changes of acceleration in x, y or z axis, one can reassemble the skier position during his run. Then with additional information about user physical characteristics (weight, heights distance from ankle to knee and hip, etc.), compute forces applied to the ski edge and experienced by the skier body.
Assuming moderate sampling rate of 1 kHz and 100 km/h speed, the exact skier position in regarding to the slope and ski as well as forces he applies to the ski edges and forces his body is experiencing, are calculated every 2.8 cm along the length of his run.
These piece-wise data are interpolated to provide continuous picture of the run and when superimposed over the graphical representation of the user, it provides realistic graphical representation of the run associated with the information obtained during the analysis.
Such graphical representation with corresponding moments may be reviewed in a real-time and transmitted to the coach wireless terminal, who in turn can feed back the advice to the user over the same wireless link or any other means of communication, or may be transmitted over such wireless network to the server for future off-line analysis, or may be stored locally within the monitoring application RAM.
Further improvements are possible when such monitoring/analysis system is augmented with the feedback mechanism providing commands to MEMS actuators placed inside the ski equipment. Such actuators can change the forces applied to the ski edge be extending or contraption of the ski edge length, provide vibration damping mechanism or instantaneous release of the ski/ski boot connection when certain dynamic forces are present.
An example of such system is presented in
Sensor 110 of
The exemplary monitoring application 300 of
At the predefined sampling rate the monitoring application 300 sends command to the PAN Media Access Layer (MAC) 211 requesting current measurements. In response the MAC layer retrieves data from each sensor in sensors using RF interface 211, than transfers such data into the monitoring application memory.
Various sensors such as accelerometers, gyroscopes, magnetometers 110, of
Results of such calculation may be then presented in a form of data tables or graphs and synchronized to the real-time video of the run or superimposed over graphical representation of the user.
The piece-wise representation is post-processed (interpolation, smoothing, rendering, etc), by the analysis application then the entire run is recreated in graphical form or synchronized to teal-time video with forces presented in form of graphs and tables. Such representations can be stored in the wireless terminal local memory for later use, or transmitted over the wireless network 400 to the remote location 600.
The safety parameters of ski/ski-boot interface are calculated every sampling period based on user physical parameters and data from sensors, such as speed, moments applied to certain parts of the skier body, moments on the ski edges, relative (to each other and the slope) ski position, etc. When the instantaneous ski/ski-boot interface value exceeds the dynamic safety threshold for any of the skis a release command is sent to both ski bindings, does eliminating the danger of fall with one ski still attached to the skier leg.
To allow full analysis of the run, beside data received from various sensors, other information specific to the user and his equipment, and if applicable—topology of the run, should be provisioned into application memory.
The first such information may contain user physical parameters, for example: user weight, height, ankle to knee distance, ankle to hip distance, hip to shoulder distance, length of the arm, etc. Such parameters are easy obtained by the user and may be entered among the other methods manually through the mobile terminal UI, or through imaging, by scanning of the QR-code of bar-code or an NFC tag attached to skier clothing.
Additional parameters may include location of the sensors, for example: in skis, ski boots, ski bindings, knee, hip, shoulder, elbow, glove, top of the ski poll, etc. as well as distance between some (or all) of them, for example: distance between ski boot and knee sensor, distance between knee and hip sensor, etc. Such information may be entered into the application manually through the UI or obtained automatically or by other means, such as: scanning of the QR-code or an NFC tag attached to ski equipment, radio ranging, differences in barometric pressure, etc.
The second such information may contain physical characteristics of the ski equipment; such as but not limited to: total ski length and weight, length of the ski edge, turning radius, stiffness/elasticity of various parts of the ski (tip/tail/etc.), ski boots and bindings types and settings, etc. Such parameters may be embedded into the QR-code or an NFC tag attached to the equipment. In addition, when the monitoring application operates in the active mode, the location and type and characteristics of MEMS actuators, for example: edge extension/contraction, vibration damping, etc. tables are included. Such parameters may be obtained from the manufacturer supplied in form of encrypted data files, such as QR-code or an NFC tag attached to the equipment. Such data files can be downloaded over the air during application provisioning by scanning of the QR code or an NFC tag.
The third such information may contain the topological parameters of the ski run such as 3D map(s) or topological contours, etc. Such information can be either preloaded to the application from the ski resort website or downloaded over-the-air automatically when the user transfers from one slope to another based on skier location.
The forth information may contain indication if the topology mapping is supported by the GPS (enough visible satellites plus required accuracy), or radio telemetry system installed along the ski slope or time synchronized (GPS, Galileo, etc) slope CCTV cameras, or barometric pressure transmission capability or any combination of the above. Such information may be obtained automatically by the application when the user enters any specific area.
At each sampling period, vectors from the accelerometers 110, together with the first, second, third and forth information are used by the monitoring application to calculate moments applied to various part of the user body as a moments G, N, P, R, etc., then constructs graphical representation of the user superimposed over the slope topography using information and/or a real-time video. This process is visually presented in
When the system is operating in the active mode as presented in
In this embodiment ski or snowboard vibrations are analyzed, then a corrective signal is generated and sent to the actuators embedded in the ski to cancel such vibrations.
It is well known that ski or snowboard turns when moments are applied to the ski edge by skier body position in relation to ski slope and the skier speed, and the turning performance is determined by the centrifugal force and the reaction to this force introduced by ski-snow contact.
To achieve tight turning radius, the ski sideline edge is curved and ski is made flexible to allow bending during the turn and avoid rolling. To improve the experience of skiing, manufacturers introduced skis with strong sideline curvature—broader tip and tail and narrow center, and high flexibility.
Since such design leads to large vibration amplitudes, manufacturers produce skis with different stiffness factor to balance the needs and experience of broad range of skiing enthusiasts, from beginners to professionals. In effect, soft and highly flexible skis, targeting average expertise levels and/or soft snow have tendencies to vibrate excessively at high speeds or in tight turns or hard or icy snow, while less flexible or stiffer skis, targeted for experts are difficult to control by an average skilled user. However, all skis, regardless of their design parameters will vibrate in turns does loosing the edge contact with the snow making edge control difficult and increases discomfort and decreases safety and performance.
Depending on the speed and snow condition, ski vibrates at several bending and torsional frequencies with the amplitudes of such vibration dependent on ski construction—stiff and hard ski may have lower amplitudes at some frequencies but are difficult to control by an average user, while soft ski may be easy to control but have higher vibration amplitudes. In general, the ski bending frequencies are between 10 Hz and 100 Hz, while the torsional frequencies are in the range of 100 Hz to 150 Hz.
An exemplary ski 700 of the prior art and it's cross-section A-A is presented in
The core 701, is a central portion of the ski which main function is to provide strength and flexibility and usually made of wood, such as poplar, ash, etc. or honeycomb metal or structural foam. Such core is encapsulated between top 702, and bottom 703 composite layers made of materials such as glass, carbon or carbon-kevlar fibers and ABS sidewalls 704. For a very stiff ski, for example race skis, the composite layers 702 and 703, may be augmented with high tensile strength aluminum alloy layer such as titanal. A layer of fiberglass 705 is added between the lower composite “wrap” of core and the base 706, which provides low resistance sliding on the snow and may be made of sintered polyethylene. The carbon steel edge 707, function is to provide ‘grip’ to the snow during turns. The main objective of such “sandwich” construction is to provide ski with necessary stiffness while preserving flexibility does allowing easy turns in all snow conditions. Those skilled in art will recognize that the present invention is not limited to the above described ski construction, but may as well be used in other type of skis, such as “cap” or “semi-cap” construction.
The shape and multi-layer/multi-material construction of ski is intended to provide the strength and ability to bend, such “natural” ski bending: 710, 711 and 712 is presented in
When ski travel at higher speeds over hard and/or uneven snow, ski starts to vibrate at several harmonic frequencies, and while the ski traverses from one turn to another, or from one type of ski/snow interface conditions to another, the amplitudes of the bending frequencies may change before it's amplitude decays. When vibration frequency, or their harmonics are similar, or the phase of the amplitudes are equal, such amplitudes will add producing even larger vibrations. The effect of such bending vibration on the ski and it's gliding capability and the induced vibrations in time and frequency domains are presented in
As seen in
After analysis vibration induced bending and torsional forces may be controlled and canceled entirely by providing feedback to the actuator sub-system embedded in the ski presented in
Location, orientation, number of actuators and their dimensions may differ from the exemplary structure presented in
The robust, chevron stale (bent-beam) thermo-electric MEMS actuator 120 offering large design and fabrication flexibility is presented in
The control signal for such thermo-electrical actuator is applied to the anchor terminal pad 1202, permanently attached to the end wall of the actuator enclosure, heats the beams of the stacked actuators 1203 providing thermal expansion caused through the Joule heating of the beams Such expansion is transferred into displacement of the movable shuttle 1204. The force 1205 and the distance 1206, the movable shuttle is displaced due to the heating effect is proportional to the current and grows with the number of stacked actuator beams.
An example of such vibration control system is presented in
Such sequence x[n] of length satisfying bandwidth of the vibration frequencies and the desired resolution is expressed as:
and after processing by the Discrete Fourier Transform (DFT) 3101, provides an approximation of the continuous Fourier transform function:
X(f)=∫−∞∞x(t)·e−i2πftdt.
The power spectral density (PSD) of ski vibration is estimated and the results applied to the classification and thresholding function 3102.
This PSD (frequencies and amplitudes) of ski vibration is first classified in terms of fundamental and harmonic frequencies and is presented in
Classification for bending and torsional frequencies is used to distribute the dampening force according to the type of vibration—along the ski logitudal axis for all bending vibration, and along the perpendicular ski axis (or combination of logitudal/perpendicular) axis for the torsional vibrations, while the natural bending frequencies attributed to ski construction materials and intended to provide flexibility and the desired ski response are discarded.
Next, the composite residual vibration matrix is applied to the Inverse Discrete Fourier Transform (IDFT), function 3103, producing time domain representation of the residual vibration signal. Such signal, is normalized in function 3104, before it's applied to the 2nd order control function 805, of a general form G(s)=Gdc/s2+2ξωn+ωn2), and finally at time t+Loop_Delay as a control signal to the actuators.
Before this time domain representation of the residual vibration is presented to the 2nd order control loop 3105, the vibration response signal from the ski is normalized by the ski specification and calibration parameters 3120, and the user physical parameters 3106, to obtain the desired control ratio ξ. This is achieved by scaling the residual vibration at function ΣX′f[t] by ski design and calibration parameters and the user current set-up of “target ski response” parameter.
The first information 3131, contains such information as: ski length, width, weight, deflection to standard loads, etc. The second information 3132, contains data obtained during post-manufacturing calibration process of each individual ski, and contains such information as: vibration damping function Xe−ξω
The ski design 3131, calibration 3132, information and the precoded messages 3133, is entered to the application memory by scanning of the QR-code or NFC tag attached to the ski. The user related information is usually entered through the smart-phone user interface (UI), or downloaded from a remote location using cellular network radio interface. Information 3133, among others may contain: operational instructions; time or event or time triggered messages; event triggered advertisement—for example, after run, on the ski lift, etc. Such precoded information may be in textual or audio/visual form.
Parameters contained in information 3130 and the user specific information is used to calculate the final value of the damping coefficient ξ, does “tuning” user ski to the current snow conditions or the desired type of run, for example: recreational vs. race. Such functionality is enabled by “scaling” the actuators force (displacement) does effecting the amplitude of response to the bending forces. The effect of such controlled dampening is presented in
Information 3131 (ski length, width, weight, etc.), is directly obtained from the ski design parameters—such as ski type, materials, etc., while information 3132, is obtained during ski post-manufacturing calibration process. Such calibration is necessary as the exact characteristics of each individual ski (flexibility, displacement due to bending forces, resonance vibration, etc.), may differ and are unknown a priori. Such ski calibration process is presented in
In Step 1, the deflection of the ski 700, in response to natural bending forces as described in relation to
In Step 2, the load 740, is removed after application and the ski is left to vibrate in response to such force, while the decaying function Xe−ξω
Next, the support structure 730, is placed between the center of the ski effective length and the front end of the ski effective length and the procedures described in Step 1 and Step 2 of is repeated, at which point, the ski calibration table is populated with the ski flexibility and vibration dampening parameters.
Operation of vibration control system is presented in
is performed resulting in approximation of the ski vibrations, represented by the matrix:
where:
ωN=e−2πi/N
is obtained.
Classification of vibrations as presented in
Such classification and selection is necessary for the following reasons: a), bending vibrations, which occur at a lower frequency range and cause ski to vibrate along it's logitudal axis, have higher amplitude; b) torsional frequencies, having lower amplitudes are more destructive as they cause side-to-side vibration of the ski; c) application of dampening stimulus to the fundamental vibration frequency, also effects harmonics of this frequency; d) selecting an appropriate threshold levels increases system performance by making it more resilient to noise, while lowering the processing requirements and power consumption; e) if actuator configuration allows (
In Step 5, the resulting matrix is applied to the Inverse Discreet Transform (IDFT) 3103, does producing time domain representation of the residual ski vibration signal. Such inverse transform can be obtained by inverting the resulting frequency matrix
In Step 6, signal representing frequencies and amplitudes of vibrations selected for dampening, is normalized (scaled), by the ski design 3131, calibration 3132, and user parameters 3106, to produce the desired control ratio coefficient ξ. This may be achieved by employing one of the suitable techniques well known to those skilled in art, such as: Least-Squares Estimation, Discrete Optimal Estimation, or by simple scaling the measured response signal by the “reference” signal derived from calibration parameters and user set-point parameters. The coefficient ξ controls the gain of damping function Xe−ξω
In Step 7, control signal G(s)=Gdc/(s2+2ωn+ωn2), is generated and send to the actuator sub-system over the smart-phone Bluetooth radio interface 211.
It has to be noted that step 6 and step 7 may be implemented as a well known PID (Proportional-Integral-Derivative), controller of the form:
Such controller may be implemented in an appropriate to the particular smart-phone programming language, such as: C, C++, or Java. An exemplary C code of a PID controller follows:
Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.
This application is a Continuation in Part application of non-provisional application Ser. No. 13/024,070 titled “Wireless System for Monitoring and Analysis of Skiing” filled on Sep. 2, 2011, which claims benefit of priority under the 35 U.S.C. section 119 of Provisional Application No. 61/310,584 titled “Wireless System for Monitoring and Analysis of Skiing” filed Mar. 4, 2010, which are hereby incorporated by reference in its entirety as though fully and completely set forth herein.