The torrent of technological innovation over the last 15 years has done little to change the way most people usually interact with their personal computers, which is generally by sitting in front of a keyboard, mouse and monitor.
The problem with the traditional method for a human interacting with their personal computer is that the human body is not suited to sitting for hours at a time, particularly while typing, pointing, clicking, and staring at an illuminated screen. This combination is further frustrated in that it can lead to muscle strain, fatigue and stress. Still, experts in ergonomics say there are several easy and effective ways in which computer users can improve their physical comfort, fight fatigue, and reduce the risk of injuries from repetitive motions.
Posture is one area in which minor adjustments can quickly yield benefits. Even at home, but especially in a more stressful environment like an office, users may force their bodies into rigid positions that result in fatigue and muscle strain. Maintaining what experts call optimal ergonomic positioning can increase energy level and improve overall comfort, although it may take a few weeks before the results are noticeable. Good posture keeps the spine in what health professionals call the neutral position.
One of the most common accessories for a personal computer (PC) is a mouse for translating motion of a user's hand into signals that an attached PC can use to move a cursor or pointer on a display. Computer mice can be found in a variety of physical embodiments. Typically, a mouse comprises a body that serves as a grip for the user's hand and as a structure for mounting a movement sensing system and two or more mouse buttons for selecting computer functions. Mice are available with electro-mechanical, opto-mechanical, or optical movement sensing systems. The electro- and opto-mechanical systems typically incorporate a ball arranged for rotation in the body and protruding from the bottom of the mouse into contact with the surface on which the mouse is resting. Movement of the mouse causes the ball to rotate. Electrical or optical transducers in the body convert the motion of the ball into electrical signals proportionate to the extent of movement of the mouse in x and y directions. The motion of the mouse can also be sensed with an optical system. One optical system requires a special mouse pad with grid lines on a reflective surface. As the mouse is moved over the grid, changes in the direction of reflected light are optically detected and transformed to electrical signals. Another mouse employs a digital camera to take periodic photographs of the surface on which the mouse is moved. A digital signal processor analyzes the series of images to determine the direction and extent of motion. Typically, the electrical signals generated by the movement sensing system are converted to a serial, digital data stream by a microprocessor in the mouse and sent to the computer over a cable or by infrared or radio frequency signaling. The computer uses the x and y movement data obtained from the mouse to repeatedly recalculate the position of the cursor on the display.
Most prior art mice have a generally horizontal, primary supporting surface for supporting a hand in a horizontal position, as exemplified by the drawing figures of U.S. Pat. No. 5,157,381 to Cheng, and the drawings in the user's manual of the Microsoft Mouse. However, such prior art mice force the hand, wrist, and forearm to be twisted 80 to 90 degrees out of their natural and relaxed positions, and require constant muscular force to be applied to the hand, wrist, and forearm to maintain their positions. For a three-button mouse, the fore, middle, and ring fingers must be kept in constant tension to prevent them from resting too heavily on the buttons and depressing them inadvertently. A horizontal hand holding a prior art mouse is supported on the desk by only a small area at the wrist on the little finger side, so that a pressure sore may develop thereon. The total effort and discomfort may not seem great at first, but when these mice are used over a prolonged and continuous period of time, users may get diseases associated with the use of the computer mouse (e.g. tendinitis, bursitis, and carpal tunnel syndrome) and experience fatigue, discomfort, and even pain in the hand and wrist.
As the use of a mouse has become more universal, ergonomics has assumed an increasing role in mouse design. For example, mice can be obtained that are designed for either right-handed or left-handed users.
U.S. Pat. No. 6,031,522 to Strand discloses an ergonomic mouse having a removable body shell. The shell fits over a base mouse that includes a movement sensing system and switches. Different shells can be installed on the base mouse to accommodate varying hand sizes, different handedness, or varying numbers of buttons for different computers, applications, or special user requirements. A mouse designed for either right- or left-handed use improves user comfort and efficiency and may reduce injuries related to mouse use. Such a mouse is acceptable and desirable if the computer has a single user. However, in a home environment, a computer may be used concurrently by a number of users of different handedness. Likewise, in libraries, schools, and other applications where computer use is shared, a mouse shaped for ambidextrous use is highly desirable, if not necessary.
U.S. Pat. No. 6,072,471 to Lo discloses an ambidextrous upright computer mouse having a relatively upright finger engaging side on one side and a thumb engaging side on the opposite side. Two sets of buttons are positioned at opposite ends of the finger engaging side. When the finger engaging side is on the right side, the mouse can be grasped by a right hand, and when the mouse is rotated so that the finger engaging side is on the left side, it can be grasped by the left hand. Only one set of buttons is enabled at any time, and the buttons are alternately enabled and disabled by moving a selector switch.
U.S. Pat. No. 6,373,468 to Leman similarly discloses a pointer device having an ergonomically contoured shell with a first set of one or more button tabs at a first end and a second set of one or more button tabs at a second end. The shell can be removably coupled to a base, and one or more switches are adapted to be activated by the first set of one or more button tabs when the shell is coupled to the base in a left-handed configuration and activated by the second set of one or more button tabs when the shell is coupled to the base in a right-handed configuration.
Standardization of the function associated with a particular mouse button is another ergonomic aspect of mouse design. One button is typically positioned for more convenient actuation by the index finger and a second button is positioned for actuation by the middle finger. Typically the cursor select function is assigned to the mouse button operated by the index finger because the function is the predominant function initiated by mouse operation. Standardization in function assignment increases the convenience of mouse operation and reduces learning time. However, standardization of function assignment presents a problem when a mouse is used by persons of different handedness. If a function is assigned to the left mouse button of a right-handed mouse (the button operated by the index finger of the right hand), a left-handed user of that mouse must actuate the button with the middle finger to obtain the same function. This operation may be awkward and is confusing if the user also operates a computer with a left-handed mouse. Computer operating systems typically provide for reassignment of functions for left- and right-handed mice. While this is useful in maintaining the desired relationship between the finger used to initiate the function for right-handed and left-handed mice, it increases user confusion if a mouse with an opposite button-function relationship is used. Further, many computer users may not be sufficiently familiar with the operating system to find and change the function-button relationship.
In addition to the movement sensing system, the mice are generally equipped with at least two mouse buttons for selecting and initiating computer functions. A mouse may be equipped with additional buttons, and mice are available with other forms of user input devices, such as finger operated rollers, that can be used to move a cursor in a displayed electronic document.
Typical computer mice, such as the one shown in U.S. Pat. No. D302,426 to Bradley et al., are substantially wider than they are tall, and have generally symmetrical sides so that they can be used by either the right or the left hand. Some mice are specially shaped for providing an optimal fit for a user's right hand. The mouse shown in U.S. Pat. No. D328,597 to Clouss, and sold under the trademark “MouseMan” by Logitech Inc. in Fremont, Calif., has a slightly angled but generally horizontal top surface for supporting the fingers and palm of a right hand. The Microsoft Mouse, Version 2, sold by Microsoft Corporation in Redmond, Wash., includes a concave left side for closely engaging the base of the thumb and palm of a right hand. The mouse shown in U.S. Pat. No. 4,862,165 to Gart includes a surface for supporting some fingers in substantially curled positions. Some ergonomic mice, including the Logitech MouseMan™, are also made in left-handed versions.
A detailed discussion of the “position of function” may be found in, for example, The Hand (1985) Vol. II, Chapter 53, pp. 497-501, published by W. B. Saunders Company, the disclosure of which is hereby incorporated by reference as though fully set forth herein. The position of function relates to the position of the hand at rest, which assumes a certain position. This is largely a mid-position of the range of motion of each and every joint, including the wrist, and rotation of the forearm. The forearm is halfway between pronation and supination. The wrist is in about 20° of dorsiflexion and 10° of ulnar flexion. The fingers are slightly flexed in each of their joints, the index being flexed least and the little finger being flexed the most. The thumb is forward from the hand in partial opposition and its joints are also partially flexed. A more precise description of the position of function can be made with regard to the thumb. In this position, the angle between the first and second metacarpal is about 45°. Each and every “position of function” must endeavor to bring together a number of favorable conditions that are not always compatible with each other. They are those that place the joints in a position in which grasp is easy, in which stiffness is less likely to occur, and, finally, in which eventual stiffness will permit preservation of movements of small aptitude, in a useful range. To that concept we add a concept from the medical field: a position of work used during a prolonged period constitutes a form of immobilization (in function). “There does not exist a ‘position of function’ in immobility; the function of the hand necessarily involves movement.” The Hand, Vol. II, Chapter 53 at 501.
As noted previously, an attempt has been made in the prior art to address these concerns of form and function. U.S. Pat. No. 4,862,165 to Gart discloses a mouse having an arched metacarpalphalangeal support surface for supporting the anterior surface of the hand and a concave thenar pad support surface for supporting the thenar pad of the hand.
U.S. Pat. No. 5,726,683 to Goldstein et al. discloses a mouse having a top surface, a right side surface, and a substantially vertically rising left side surface. The top surface has a negative slope from front to rear in a range of 15°-30° and from left to right in a range of 20°-30°, and provides at the front of the top surface a phalanx support. The top surface includes a peak running from front to back oriented to lie under the operator's thenar eminence providing support thereto and a surface through which the operator can push the mouse with his or her thenar eminence.
U.S. Pat. No. 5,894,302 to Scenna et al. discloses a mouse including an upper surface having a hump for supporting the triangular area of the hand encircled by the thenar region, the hyperthenar region, and the region below the metacarpal-phalangeal joints. The upper surface includes a tail having a rising portion to underlie and bear the pressure of the region of the user's hand where the thenar and hyperthenar converge. The finger buttons in the front are elevated above the hump.
By way of further background, a reported cause of carpal-tunnel syndrome is improper use of a computer mouse pointer. With a conventional mouse the users can develop bad habits that may predispose them to development or aggravation of carpal-tunnel syndrome. These bad habits can include using excessive wrist angles to position the mouse pointer instead of using the forearm and fingers, such as placing the wrist flat on the desk surface with the wrist bent back at an angle greater than fifteen degrees, and pronation (inward rotation) of the wrist past a normal angle with fingers spread to reach around the mouse body and then gripping the mouse tightly. With the hand in any of these positions, finger motion (clicking) is believed to potentially irritate the tissues and nerves in the carpal-tunnel. Indiscriminate use of wrist or arm braces can exacerbate the effects.
There have been several attempts to solve these problems. Mice have been designed with palm knobs and enlarged square ends. These designs, however, aggravate the above identified problems. The thumb and ring finger are brought into constant contraction and require the continual extension of the index and middle fingers over the activating buttons causing stress of the tendons in the forearm. As with other mouse designs, the ring finger is necessarily placed on the side of the mouse, leading to the myriad of problems outlined above.
Additionally, pronation of the hand is increased. By elevating the palm, the left stretch of the forefinger is increased and more reach is required thereby necessitating increased pronation. While these designs may provide some hand support, there is no finger extensor relief and they restrict fine finger control.
Heretofore, most hand operated data input devices have forced the user to position his/her hand in a position that is substantially parallel to the work surface. It has now been discovered that such a position places the user's hand at risk for a repetitive motion injury. Instead of a position that is substantially parallel to the work surface, it has now been discovered that the risk of injury is lessened if the hand is placed in supernated position at any angle up to an angle of about 90°. However, an angle of about 45° with the work surface appears to be the optimum.