Engineering a Smooth Ride: Creating the Perfect Ski Through Shaping and Vibration Damping
About the Author: Brent Nash
In spring of 2002, Brent Nash was a 20-year old Computer Engineering and Science major at the University of Southern California. As a student, he was an avid skier.
Although snow skis appear to be very basic products, the engineering behind them is surprisingly involved. The type of skiing and type of snow conditions dictate the required ski geometry. Avid skiers have longed for a high-performance, all-around ski. Vibration caused by high speeds and tough terrain has been a significant problem faced by engineers in the pursuit of such a design. Recently, however, engineers have developed skis that incorporate vibration control technology. This “Smart Ski” technology solves the vibratory problem through the use of piezoelectric ceramics. These ceramics detect vibration by sending an electrical signal to an on-board processing circuit, which then triggers mechanical actuators to cancel the unwanted vibration. Thus, the Smart Ski has demonstrated the complex technological intricacies hidden in the seemingly simple realm of ski engineering and manufacture.
Engineering a Smooth Ride: Shaping and Vibration Damping in Ski Design
Skis may appear to be relatively simple products without much room for high-tech engineering, but this is far from the truth . Modern ski designers and engineers are on a never-ending quest to create a faster, lighter, more responsive and more durable product. These attempts have resulted in the creation of skis of all shapes and sizes using materials ranging from wood to synthetic fiber. The ski manufacturing process is an incredibly complicated science. Tests have shown that varying ski shapes and styles are more suited for different conditions . Because each ski type possesses unique benefits and detriments in different conditions, a skier can be well suited for skiing conditions at one moment yet unprepared the next as snow conditions change. In addition, most ski designs must cope with an inability to eliminate unwanted vibrations that can compromise ski stability, one of the biggest problems facing the modern ski manufacturing industry. A new technology has emerged to overcome these limitations by utilizing a unique shape and the integration of piezoelectric sensors and an actuator control system.
Shaping the Smart Ski
The first step in the creation of an all-purpose, all-mountain ski is to determine the shape characteristics of the ski. This shaping decision is no easy task for engineers due to the numerous benefits and detriments associated with different ski shapes. Longer skis provide greater stability and control at high speeds, but are harder to maneuver while shorter skis are easier to turn and maneuver, but are less stable (see Fig. 1). Wider skis ride better on soft, powdery snow while hourglass-shaped skis with a large sidecut turn better on hard snow and ice. Engineers ultimately decided to create a short, wide, hourglass-shaped ski. The wideness of the ski would allow for better riding on soft, powdery snow because the rider’s weight would be more widely distributed over a larger area of the snow. This wider distribution would serve to create a buoyant riding effect, allowing the skier to almost “float” on top of the snow. In contrast, the hourglass shape of the ski would allow for a more smooth and controlled ride on hard-packed snow and ice. With their hourglass shape, the skis concentrate more of the skier’s weight on the blade edge at the middle of the ski, allowing it to dig deeper and make sharper turns. Finally, the shortness of the ski allows for increased skier control. With a shorter ski, there is less ski surface to redirect when changing directions, making the skis easier to turn . Recall the trendy “Bigfoot” short short skis of the 1980s, popular with beginners because they were easier to turn than longer skis.
By combining the hourglass shape, a wide base, and a shorter ski, engineers brought together the benefits of all three designs. The wider base and the hourglass shape of the ski complimented each other well because the former facilitated soft snow riding and the latter improved hard snow riding. Unfortunately, the shortness of the ski created a major maneuverability problem. All skis are subject to unwanted vibrations, especially at higher speeds, but testing has proven that shorter skis have a tendency to have more frequent and more powerful vibrations than longer skis . At first glance, vibration as a problem does not seem incredibly difficult, but vibration and instability are actually very difficult to counteract.
Causes of Vibration and Associated Problems
Most often, uneven snow surfaces can cause a ski to vibrate, forcing the ski to lose contact with the snow. Shorter skis and harder surfaces tend to exacerbate the vibrational problem. Skiing on a bumpy or hard-packed run is comparable to driving a car down a gravel road . The increased vibrations caused by the uneven gravel surface can lessen a driver’s control behind the wheel. As Anthony DeRocco, K2 director of product development, asserts, “Vibration control on skis works much like a car’s suspension system, which improves control by maintaining contact between the tires and the road. If there is air between tire and road, no amount of steering will have any effect. The same is true for skis and snow: no contact means no control” . By lessening the contact of the ski with the snow, vibration diminishes a skier’s turning ability, stopping ability, and overall control, which can be dangerous to both the skier and those around him or her. In reality, both uneven snow and reactionary forces between the snow and a rider’s skis are the cause of all vibrations. The challenge in counteracting vibration is attempting to gauge these reactionary forces, and then subsequently identifying ways to diminish their effects.
Difficulties with Counteracting Vibration
The reactive forces between a rider’s skis and the snow are constantly changing during a downhill descent. These reaction forces can be varied by a number of factors ranging from snow softness to a skier’s motions and actions. Because of the dynamic nature of these reaction forces, every skier will experience different forces every time they descend a run . Ski runs, a skier’s turning, and even snow softness are never constants, and therefore it is virtually impossible to create an anti-vibratory mechanism to control a specific type or pattern of vibration, because vibrations change unpredictably with every run down the mountain.
Not only does vibration occur in a random and unpredictable fashion, but when it does occur, it results in non-linear and disproportionate vibration strength and location. On-snow tests show that the majority of vibrations are centered, or at least originate, in the area around the ski binding. From the boot area, however, the vibrations distribute themselves disproportionately over the entire ski. Laboratory experiments and on-snow tests have shown that the tail of the ski vibrates independently of the tip of the ski (see Fig. 2). In fact, it is generally the case that the ski tail vibrates with only 20% of the magnitude of the tip vibrations .
In general, because of the random nature of ski vibration and the unpredictable nature of reactionary forces between the snow and skiers, it is incredibly difficult to simulate real, on-slope conditions in a laboratory environment. Different stress and weight tests have been performed by numerous engineers on a wide range of skiing equipment, but scientists still have difficulty nailing down consistent data readings . Because of this, many times it is very difficult for manufacturers to know how a ski will perform before its construction. This, unfortunately, leaves many manufacturers in the dark on how to go about finding a systematic testing and design process. Some engineers have said that dampening vibration is not necessarily the most difficult part of construction, but rather the most difficult problem lies in creating a ski that can dampen vibration and still be responsive and versatile on the slopes. Many skiers used in on-slope tests have complained that skis with too much damping and vibration control feel lifeless and unresponsive on their feet . This unresponsiveness creates a control problem on a whole new level. Creating a ski with a well-rounded design and the right amount of vibration dampening has been an enigma that has puzzled the ski manufacturing industry for years.
The Piezoelectric Solution
Despite the numerous problems and hardships encountered during the attempted development of the all-around ski, engineers did not give up without researching every possible solution to their vibrational problem. Eventually, K2 engineers teamed up with engineers from Active Control eXperts (ACX), in an attempt to use piezoelectric ceramics in their vibrational dampening endeavors. A piezoelectric element is a ceramic that will generate an electric charge when it is stressed mechanically by a force . In the case of skiing, it is already known that many reactive forces exist between a rider’s skis and the snow, but it also follows that these reactive forces can cause the ski to flex and vibrate during a run. K2 and ACX engineers noticed that if piezoelectric devices were placed into a ski, then when vibrations caused a ski to flex and begin to lose contact with the snow, the piezoelectric devices would be flexed, or mechanically stressed as well, and would thereby create an electric charge. In addition, piezoelectric devices have the advantage of being relatively unobtrusive in the realm of size and possess the ability to function independent of temperature changes. Installing the piezoelectric devices would prove to be quite difficult, however, because they are very brittle. They need large amounts of shielding and protection, but at the same time they must be free enough to flex and produce electrical charge . These electric charges are harnessed and used to counteract vibration.
The final solution reached by engineers consisted of a relatively simple, but ingenious setup consisting of three main components: three piezoelectric elements, a simple electrical circuit, and protective packaging. The three piezoelectric elements were relatively tiny pieces of ceramic imbedded in the interior of the ski directly in front of the toepiece of the skier’s boot. According to Anthony DeRocco, “The area of the toepiece is the best place to shut down vibrations” . Tests have shown that the majority of vibrations are concentrated in the area of the ski binding, near the toepiece, and propagate outwards to the rest of the ski. Once the ceramics were obtained, they had to be protectively packaged before being placed into the ski. Although the piezoelectric components are incredibly resistant to temperature changes, they have a rather fragile nature that makes their durability and operation dependent upon receiving enough stress to bend, but not enough to cause them to break. As a result, the piezoelectric ceramics in the K2 Smart Ski were encapsulated in a tough polyimide shell with electrical leads issuing from the shell so that electrical charge could still flow out of the ceramic and out of the shell. The polyimide shell is “a synthetic polymeric resin resistant to high temperatures, wear, and corrosion,” making it a great all-around protective shell for the piezoelectric elements due to its tough and durable nature . Finally, the piezoelectric ceramics themselves were wired inside the ski into a small electrical circuit, creating a loop in which electric charge could flow.
Once the circuit and all its components were in place, the ski was able to dampen vibration like no other equipment ever manufactured. As noted, when vibrations cause the ski to flex or bend, the piezoelectric elements will flex and bend as well, producing an electric charge and current to drive the ski’s internal circuitry. This current uses the internal circuit to create a strong electric field that causes some of the smaller circuit elements, known as actuators, to oppose external vibrations. The result is that the unwanted vibrations throughout the ski are quickly canceled out, leaving a much greater portion of the ski in contact with the snow . So, in essence, there is a three-step process to how the piezoelectric devices can dampen ski vibrations. First, the piezoelectric elements detect vibrations and send an electric signal. This signal is then received and an electric field is produced to oppose the vibration. Finally, this electric field triggers internal actuator elements to oppose external vibration and thereby cancel out any unwanted vibrations.
Through their engineering expertise and innovation, K2 and ACX have combined to create a state-of-the-art, all-around ski. By combining the shape and structure of many one-dimensional skis, K2 created a versatile ski that could ride well in any set of conditions. Furthermore, by adding a vibration dampening system using piezoelectric ceramics and electrical wiring, K2 revolutionized the ski industry by bringing vibration control systems to the mass market. Due in large part to these two design innovations, the Smart Ski project was a huge success. After demonstrating its beneficial capabilities in a number of laboratory and on-snow tests, the Smart Ski technology has now appeared in many K2 skis on the market today such as the “Four” and the “Merlin V.” K2 and ACX engineers hope that future models and designs will even improve upon the capabilities of their current skis by enhancing overall vibration control. K2 claims that their skis of the future will be able to use their inner circuitry and piezoelectric elements to not only detect and dampen vibration, but to even detect changes in speed or damage to the ski itself and adjust the ski’s performance accordingly. At first glance, a ski might appear to be an uncomplicated piece of equipment, but further inspection reveals that the intricacies of the modern ski are numerous and complex. The trials, tribulations, and ultimate success of the Smart Ski project serve as a very tangible example of how complex engineering can greatly improve seemingly simple technology.
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