Redesigning a Curling Iron
DEA 325 - Homework 3
November 24, 1997
Every day, as millions of women get ready for a day of work or school, dress for a social event or prepare for any occasion, thousands of curling irons are turned on. Each day in beauty salons, thousands more are turned on to be used on the myriad of clients appearing throughout the day. And while many changes have been made in the size of the curling rod and the heat levels that can be achieved, few of these changes, if any, have considered the ergonomic needs of the users.
In redesigning this hand tool for the hair, I focus on the three major segments of the curling iron: the handle, the rod and the tip. These segments are labeled on a traditional curling iron in Appendix A.
The activity for which the curling iron is most commonly used is curling pieces of hair. However, curling irons can also be used to straighten hair or to warm hair for easier styling. Wig makers may use curling irons to create waves in both natural and synthetic wigs. Most curling iron users are women, although male hair stylists, wig makers, and perhaps men frustrated with their own straight hair make up a portion of the user group. Curling irons are used both by those curling their own hair and those curling the hair of others.
In this paper I will discuss my redesign from each of the three segments of the traditional curling iron. The redesign sketches can be seen in Appendices B, C, D, and E.
Handle - Traditional
The traditional curling iron has a handle that is an extension of the rod in both size and shape. The cylindrical rod flows into a smooth cylindrical handle. The three commonly found sizes of curling iron rods are 1", 1-1/2" and 2" diameters.
To turn a curling iron on, most have a switch-pad that slides up or down to be turned on or off, in some cases having different settings such as low, medium and high (see example in Appendix A). Often the sliding switch is moved accidentally when using a curling iron, which can turn off the heat without the user realizing it until the rod is cold and will take minutes to warm up again. Some have a separate on/off switch and a rotating knob that controls heat settings. And the simplistic curling iron turns on when plugged in and off when unplugged. Perhaps one of the best innovations in curling irons of late is the automatic off setting, where a curling iron that has been unused for a certain amount of time automatically shuts itself off, for fire safety reasons. Most models available today have an indicator light that tells the user if the rod is on/hot or off.
In order to raise the clasp on the rod, the thumb must be used to press on a lever. The lever is in reach of the thumb, even when all four fingers are clasping the handle.
Handle Redesign (Appendices B & C)
Several new features have been added to the newly designed handle (Appendix B). The most noticeable difference is the angle of the handle from the rod. In this case, I used Bennett's idea of "bending the tool, not the wrist" (Emanuel, Mills, and Bennett in Sanders and McCormick, 1993) and Lewis and Narayan's (1993) recommendation that while working, the handle and the forearm should be aligned. The new angle of the handle, approximately 100 degrees, reduces ulnar deviation, which occurs with the traditional straight handle. Minimizing ulnar deviation reduces the possibility of carpal tunnel syndrome, tenosynovitis and tennis elbow in frequent users. The handle also reduces shoulder abduction because the arm will not need to be raised as high when curling hair as with a traditional handle. This will reduce stresses on the shoulder joint, which could otherwise lead to increased muscle fatigue and cumulative trauma disorders (Hedge, 1997; Schoenmarklin & Marras, 1989). The new handle needs little assistance from the upper arm and shoulder because the lower arm can easily reach the angled handle simply by bending the elbow. Another benefit of angling the handle is that changing the shape of the curling iron from a flat shape to a pistol shape shifts the curling iron's center of gravity. This shift provides a more even weight distribution for the user and minimizes the possibility of the uneven weight of the curling iron causing it to twist out of the user's hand (Armstrong, Radwin & Hansen, 1986; See Appendix F, Diagram 2).
Another change from the traditional handle is the method for opening the clasp. In traditional models, the thumb must apply significant pressure on the clasp lever in order to raise the clasp, leading to increased fatigue in the thumb muscles and joints. In addition, the thumb is in an hyperextended position, which can cause pain and inflammation (Sanders and McCormick, 1993). The redesign has the user holding the handle like a pair of pliers. This design spreads out the pressure needed to open the clasp to all the digits by using handles similar to those in a pair of pliers (See Appendix F, Diagram 1). Squeezing the two handles together raises the clasp. The grip strength needed to raise the clasp is very low, approximately 10 pounds, to accommodate the 5th percentile female. This is assuming the opening of the grip axis is two inches (Greenberg and Chaffin, 1977 in Sanders and McCormick, 1993), which is the standard handle diameter size for my redesign, regardless of the rod size.
This new method for opening the clasp affects the shape. Because a contoured hand tool decreases slippage (Hedge, 1997; Lewis & Narayan, 1993), the contoured redesign provides a shape more similar to the anatomy. This correct shape was derived from the redesigned pliers designed by Damon (1965 in Sanders and McCormick, 1993) and Tichauer (1966 in Sanders and McCormick, 1993; see Appendix F, Diagram 1). This contoured shape, which is closer to that of a gun handle, gives the user more control and reduces wrist deviation (Hedge, 1997). Additionally, the bend in the handle decreases stress on flexor tendons and the median nerve, and such curves will not likely affect performance in using the curling iron (Konz, 1986; Schoenmarklin & Marras, 1989); there is little worry of a decrease in effectiveness with a curved handle. It is important to note, however, that despite the change from a cylindrical to a gun handle shape, the edges of the handle must maintain a rounded shape because sharp edges can cause cuts, bruises, or abrasions (Lewis & Narayan, 1993).
The length of the handle extends beyond the hand. Not only does this provide a more even weight distribution of the rod and handle, it eliminates the possibility of strain on the center of the palm, as handles shorter than the palm create high forces in the center of it (Lewis & Narayan, 1993).
The texture of the redesigned handle is not the typical plastic seen on traditional handles. To avoid slipping, especially as hands may perspire due to the hot curling iron, the handle is covered with a layer of thin foam. In addition to minimizing perspiration, people prefer the soft feel of foam to hard, smooth wood (Fellows and Freivalds, 1991). This is most likely due to the fact that foam increases the uniformity of force distribution from the hand, thus improving user comfort. These findings can be carried over to the curling iron handle, as a foam handle will most likely not only decrease slippage, but will also provide stronger user satisfaction.
The power switch for the redesign is a push-button at the end of the handle. The location at the bottom of the handle will eliminate a user accidentally turning off the heat while in using the curling iron. And the easy-to-push button will not strain the digit used to press it. As in some traditional designs, the heat will automatically be turned off after a few minutes of non-use. Similar to many curling irons today, an indicator light is used to tell the user if the rod is on/hot or off.
The motor button in the redesign serves to activate the motor in the rod (see Appendix D). The button is pressed by the thumb in the thumb support region. The movement of the thumb from its location for opening the clasp to its location for activating the motor is minimal, so it will not likely cause undo strain on the thumb. Additionally, note that the thumb will not be overextended (as in the traditional curling iron) while pressing the button due to the contour of the thumb support region (see region in Appendices B, C and F, Diagram 1).
To control the heat setting, the bottom portion of the handle will rotate to the desired setting. This portion is larger than that on a traditional curling iron, which makes it easier to turn to adjust the setting. This portion is serrated to assist the grip. A window in this portion will show the user the heat setting.
The traditional rod (Appendix A) attaches directly to the handle and does not move from that position. It is made of metal that quickly heats up and becomes very hot when on. The clasp of the rod is raised in order to slide a lock of hair underneath and then lowered to hold the end of the lock. As the handle is turned, the hair wraps around the rod and heats through heat radiation from the metal.
Rod Redesign (Appendices B & D)
The major new function of the redesign is the addition of a motor to the rod. This motor will serve to turn the rod with the press of a button on the handle. This eliminates the major ergonomic problem of using a curling iron, twisting the wrist over and over to wrap a lock of hair around the rod, which can cause tenosynovitis. The motor is encased in a heat-resistant case within the rod to prevent melting. As the motor button activates the rod, it will slowly spin, wrapping the lock of hair around itself. Such a motor significantly reduces the effort needed by the user.
In the redesign, a joint has been created between the rod and the handle. Because the handle is at an angle, it will not work well to rotate the handle in order to wrap the hair around the rod. This is an advantage in that the hand holding the handle will not have to continuously rotate when using a curling iron, which could lead to tenosynovitis (Sanders and McCormick, 1993). The joint allows the rod to move separately from the handle.
The other change in the rod design is the clasp. Traditional clasps, if not perfectly aligned with the rod down the entire length of the clasp, often do not grasp hair tightly enough so that the end slips out when trying to wind the hair around the rod. The new clasp is made up of two separate pieces of metal encased in fire-resistant fabric. This gives more stability to the piece of hair being clasped, as it now has twice "holding power". While not directly ergonomically beneficial, the frustration eliminated by this design feature will benefit the psychological well-being of the user.
On traditional curling irons, the main purpose of the tip is to provide a protective cover to the end of the rod when it is hot. It usually consists of a small piece of plastic.
Tip Redesign (Appendices B & E)
In the redesign, the tip is used as a rod rest. The tip is shaped like a circle with two flat edges. Each flat side will serve as a stable rest when the curling iron is laid down on a flat surface. The two flat sides gives the user more flexibility as to which side to lay the curling iron down; this flexibility also supports both right- and left-handed users. The size of the tip extends far enough beyond the rod so as to be sure the rod does not touch a surface when the curling iron is laid down. Designing the tip as a rod rest will decrease the possibility of burns and/or fires caused by this tool.
Another new function of the tip is that of the turn of direction knob. Each of the flat sides mentioned above will have soft insets. When the user squeezes these insets, the joint of the rod will loosen. The rod, and thus the clasp, can then be rotated to whichever clasp location is best for the user. This choice of direction makes the curling iron accessible to both right- and left-handers. It also provides the opportunity to switch curl direction, that is whether the user wants to curl hair under or out.
This redesigned curling iron could lead to increased user comfort and decreased hand-tool-related injuries and muscle fatigue, not to mention user frustration. By minimizing ulnar deviation, thumb hyperextension, wrist deviation, slippage, tenosynovitis, user frustration and single-hand use, the user will be much healthier and happier with the new product. Both left and right-handers can use this curling iron equally well. And due to the small amount of force needed to squeeze the handle and turn the wheel, and the fairly small scale of the tool, the users are not limited by gender.
Ergonomic design considerations can improve the well being for human beings, and whether the improvement is significant or slight, design considerations should be well thought out when creating a product.
Armstrong, T. J., Radwin, R. G., & Hansen,
D. J. (1986). Repetitive trauma disorders: job evaluation and design. Human
Factors. 28 (3), pp. 325-336.
Fellows, G. L. & Freivalds, A. (1991). Ergonomics
evaluation of a foam rubber grip for tool handles. Applied Ergonomics. 22
(4), pp. 225-230.
Hedge, A. (1997). Hand Tool Design. DEA 651 class
Konz, S. (1986). Bent hammer handles. Human Factors.
28 (3), pp. 317-323.
Lewis, W. G. & Narayan, C. V. (1993). Design
and sizing of ergonomic handles for hand tools. Applied Ergonomics. 24 (5),
Sanders, M. S. & McCormick, E. J. (1993). Human
Factors in Engineering (7th edition). New York: McGraw-Hill, Inc. pp. 383-409.
Schoenmarklin, R. W. & Marras, W. S. (1989).
Effects of handle angle and work orientation on hammering: II. Muschle fatigue
and subjective ratings of body discomfort. Human Factors. 31 (4), pp. 413-420.
Schoenmarklin, R. W. & Marras, W. S. (1989). Effects of handle angle and work orientation on hammering: I. Wrist motion and hammering performance. Human Factors. 31 (4), pp. 397-411.