lecture_11 - Human Factors in Design S. Laguette ME 128...

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Unformatted text preview: Human Factors in Design S. Laguette ME 128 Fall 2007 November 7, 2007 11/07/07 ME 128 1 Human Factors in Design HUMAN FACTORS: AN HISTORICAL PERSPECTIVE WHY HUMAN FACTORS ENGINEERING IS IMPORTANT THE USER INTERFACE HUMAN FACTORS ENGINEERING 11/07/07 ME 128 2 What is Human Factors? Application of the scientific knowledge of human capabilities and limitations to the design of systems and equipment to produce products with the most efficient, safe, effective, and reliable operation 11/07/07 ME 128 3 Human Factors Interface points Environment Skill level of user Interaction between: Human element Hardware element Software element 11/07/07 ME 128 4 Device Use 11/07/07 ME 128 5 Operating Room 11/07/07 ME 128 6 HUMAN FACTORS: AN HISTORICAL PERSPECTIVE Human factors is a discipline that seeks to improve human performance in the use of equipment by means of hardware and software design that is compatible with the abilities of the user population. 11/07/07 ME 128 7 HUMAN FACTORS: AN HISTORICAL PERSPECTIVE Historically, human factors can be traced to early efforts by industrial engineers, psychologists, and efficiency experts to streamline manufacturing operations and equipment for better worker efficiency. In World War II, emphasis shifted from production to personnel safety. A special focus was cockpit design of aircraft. Poor design of controls and displays often induced pilot errors, sometimes leading to crashes. Human factors analyses and tests became routine in the design of military and commercial cockpits. 11/07/07 ME 128 8 WHY HUMAN FACTORS ENGINEERING IS IMPORTANT A medical device can be used safely and effectively only if the interaction between the operating environment, user capabilities, stress levels, and device design is considered when the manufacturer designs the device. 11/07/07 ME 128 9 WHY HUMAN FACTORS ENGINEERING IS IMPORTANT Physical and Sensory Characteristics Perceptual and Cognitive Abilities 11/07/07 ME 128 10 WHY HUMAN FACTORS ENGINEERING IS IMPORTANT DESIGN IMPLICATIONS accommodates a wide range of users working under variable, often stressful conditions; is less prone to user error; and requires less user training. 11/07/07 ME 128 11 THE USER INTERFACE The following three examples of problems were abstracted from the Medical Device Reporting (MDR) system and FDA device recalls. A physician treating a patient with oxygen set the flow control knob, as show in Figure 1, between 1 and 2 liters per minute, not realizing that the scale numbers represented discrete, rather than continuous, settings. There was no oxygen flow between the settings, yet the knob rotated smoothly, suggesting that intermediate settings were possible. The patient, an infant, became hypoxic before the error was discovered. One solution would have been a rotary control that snaps into a discrete setting. Some indication of flow also should have been provided. 11/07/07 ME 128 12 THE USER INTERFACE There have been numerous reports and recalls associated with defibrillator design. These include paddles that are hard to remove from their retaining wells and confusing arrays of poorly-labeled controls and displays that inhibit safe, efficient use. 11/07/07 ME 128 13 THE USER INTERFACE There have been cases in which patients were seriously injured when a nurse over infused a patient after reading the number 7 as a 1. Because the flow rate readout was recessed in the infusion pump display panel, the top of the 7 was blocked from view by the display surface, even at modest vertical viewing angles. There have been similar reports of flow rates which had been misread when viewed from the side; for example, 355 ml read as 55 ml. 11/07/07 ME 128 14 THE USER INTERFACE Rules of Thumb Make all facets of design as consistent with user expectations as possible. Both the user's prior experience with medical devices and well-established conventions are important considerations. Design workstations, controls, and displays around the basic capabilities of the user, such as strength, dexterity, memory, reach, vision, and hearing. Design well-organized and uncluttered control and display arrangements. Ensure that the association between controls and displays is obvious. This facilitates proper identification and reduces the user's memory load. Ensure that the intensity and pitch of auditory signals allow them to be heard easily by device users. Consider the effects of ambient noise. 11/07/07 ME 128 15 THE USER INTERFACE Ensure that the brightness of visual signals is sufficient to be perceived by users working under various conditions of ambient illumination. Also, brightness contrast and color contrast can help to optimize legibility. Make labels and displays so that they can be easily read from typical viewing angles and distances. Symbol size, contrast, color, and display depth are important considerations. Ensure that the abbreviations, symbols, text, and acronyms placed on, or displayed by, the device are also used consistently in the instructional manual. They also should correspond to standard nomenclature, if possible. Design control knobs and switches so that they correspond to the conventions of the user population (as determined by user studies and existing medical device standards). 11/07/07 ME 128 16 Infusion 11/07/07 ME 128 17 Infusion 11/07/07 ME 128 18 Monitors 11/07/07 ME 128 19 THE USER INTERFACE Arrange and design knobs, switches, and keys in a way that reduces the likelihood of inadvertent activation. Use color and shape coding, where appropriate, to facilitate the rapid identification of controls and displays. Colors and codes should not conflict with universal industry conventions. Space keys, switches, and control knobs sufficiently apart for easy manipulation. This will also reduce the likelihood of inadvertent activation. Make sure that controls provide tactile feedback. 11/07/07 ME 128 20 Human Element Memory Long term Short term Thinking and reasoning Visual perception Dialogue construction Individual skill level Individual sophistication 11/07/07 ME 128 21 HUMAN FACTORS ENGINEERING Human factors engineering is a methodology that is crucial to effective user-interface design; iterative application of various procedures and tools throughout the design cycle, as illustrated in Figure 5 Participation of individuals from the user population is integral to this process. 11/07/07 ME 128 22 HUMAN FACTORS ENGINEERING 11/07/07 ME 128 23 Size limitations Location of controls Compatibility with other equipment Possible user training Hardware Element Control 11/07/07 knobs/switches Display area ME 128 Potential need for portability 24 Simple, reliable data entry Displays must not be overcrowded Software Element Feedback to users 11/07/07 Dialogue must ME 128 be jargon-free Menu driven 25 Human Factors Process Analytic process that focuses on device objectives Design and development process that converts results of analyses into detailed equipment features Test and evaluation process which verifies that development process satisfies constraints 11/07/07 ME 128 26 Steps in Human Factors Process Planning Analysis Conduct user studies Observations Interviews Focus groups Task analysis Benchmark usability tests User profile Setup advisory panel ME 128 11/07/07 Crucial Pieces of Human Factors Process 27 Safety Should reflect system and personnel safety factors Failures Fail safe Failure indications Standards- ANSI, AAMI, ISO 11/07/07 ME 128 28 Documentation Written to meet needs of various target populations Study capability and information needs of documentation users Mental abilities Physical abilities Previous experience Understanding of general operation Special needs of environment ME 128 29 Attempt to avoid this! 11/07/07 Labeling Labels should be clear and direct Controls, displays, and other equipment that must be located should be clearly marked Receptacles and connectors should be marked with intended function or connection Hazard warnings should be prominent 11/07/07 ME 128 30 Software Every user input should consistently produce some perceptible response from the computer Log-on should be automatically completed before any operation Allow for orderly shutdown in case of failure 11/07/07 ME 128 31 Data Entry Consistent data entry transactions Minimize user input actions Feedback to user about acceptance or rejection of an entry Ability to change entry after it has been added 11/07/07 ME 128 32 Feedback Present status, information, confirmation, and verification throughout the interaction Standby should be accompanied by `WAIT' message Feedback should be self-explanatory 11/07/07 ME 128 33 Prompts Commands, error messages, system capabilities, and procedures should be explained with prompts or help instructions Missing data/aborting changes should be prompted Factual and informative dialogue Displayed in standardized area 11/07/07 ME 128 34 Defaults Currently defined default values should be provides and automatically displayed User should be prompted for acceptance of defaults Users should be able to set their own default 11/07/07 ME 128 35 Medical Devices Medtronic is voluntarily conducting a correction of a limited number of LIFEPAK 20 defibrillator/monitors with version 28 software that were distributed between January and May 2005. The defibrillator may not operate if the device is turned on during an AC Loss Alert. If this occurs all device functions are inhibited until the device is reconnected to AC power. 11/07/07 ME 128 36 References http://www.fda.gov/cdrh/humfac/doi t.html Do It By Design - An Introduction to Human Factors in Medical Devices - Updated December 9, 1996 11/07/07 ME 128 37 References P.H. King Lecture Series 11/07/07 ME 128 38 ...
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