wsm

• Motion study


  The careful analysis of body motions employed in doing a job
• Motion study


  • Eliminate or reduce ineffective movements
  • Facilitate and speed effective movements
• Job is redesigned to be more effective and to produce a higher rate of output
• Types of motion study


  • Visual motion study
  • Micromotion study
• Therbligs


  The 17 basic motions that all work, whether productive or nonproductive, is done by using combinations of
• Effective therbligs


  • Directly advance the progress of the work
  • Can frequently be shortened, but typically cannot be completely eliminated
• Ineffective therbligs


  • Do not advance the progress of the work
  • Eliminated by applying the principles of motion economy
• Two-hand process chart


  A motion study tool that shows all movements and delays made by the right and left hands, and the relationships between them
• Two-hand process chart


  • Purpose is to identify inefficient motion patterns and observe violations of the principles of motion economy
  • Facilitates changing a method so that a balanced two-handed operation can be achieved and a smoother, more rhythmic cycle that keeps both delays and operator fatigue to a minimum
• Creating a two-hand process chart


  1. Head the chart with identifying information

  2. Sketch the workstation

  3. Observe the duration of each element and determine the amount of time to be represented on the chart

  4. Chart the activities of one hand completely before examining the other hand

  5. Create a summary at the bottom indicating the cycle time, pieces per cycle, and time per piece

  
• Corollaries to the principles of motion economy when using a two-hand process chart

  • Establish the best sequences of therbligs
  • Investigate any substantial variation in the time required for a given therblig and determine the cause
  • Examine and analyze hesitations, to determine and then eliminate their causes
  • As a goal, aim for cycles and portions of cycles completed in the least amount of time. Study deviations from these minimum times to determine the causes
• Delays and holds are good places to begin when using the two-hand process chart
• Use the Therblig Analysis Checklist when using the two-hand process chart
• Principles of motion economy


  • The use of the human body
  • The arrangement and conditions of the workplace
  • The design of tools and equipment
• Principles of motion economy - the use of the human body

  • Both hands should begin and end their basic divisions of accomplishment simultaneously and should not be idle at the same instant, except during rest periods
  • The motions made by the hands should be made symmetrically and simultaneously away from and toward the center of the body
  • Momentum, should assist workers wherever possible, and should be minimized if it must be overcome by muscular effort
  • Continuous curved motions are preferable to straight-line motions involving sudden and sharp changes in direction
  • The least number of basic divisions should be used: these should be confined to the lowest practicable classifications
  • Work done by the feet should be done simultaneously with work done by the hands
  • The middle finger and the thumb are the strongest working fingers
  • The feet are not capable of efficiently operating pedals when the operator is in a standing position
  • Twisting motions should be performed with the elbows bent
  • To grip tools, workers should use the segments of the fingers closest to the palm of the hand
• Principles of motion economy - the arrangement and conditions of the workplace

  • Fixed locations for all tools and material should be provided to permit the best sequence and to eliminate or reduce the therbligs search and select
  • Gravity bins and drop delivery should reduce reach and move times; also, wherever possible, ejectors should remove finished parts automatically
  • All materials and tools should be located within the normal working area in both the vertical and the horizontal planes
  • A comfortable chair for the operator and the workstation's height should be so arranged that the work can be efficiently performed by the operator alternately standing or sitting
  • Proper illumination, ventilation, and temperature should be provided
  • The visual requirements of the workplace should be considered so that eye fixation demands are minimized
  • Rhythm is essential to the smooth and automatic performance of an operation, and the work should be arranged to permit an easy and natural rhythm wherever possible
• Principles of motion economy - the design of tools and equipment

  • Multiple cuts should be taken whenever possible by combining two or more tools in one, or by arranging simultaneous cuts from both feeding devices, if available
  • All levers, handles, wheels and other control devices should be readily accessible to the operator and designed to give the best possible mechanical advantage and to utilize the strongest available muscle group
  • Parts should be held in position by fixtures
  • The use of powered or semiautomatic tools, such as power nuts and screwdrivers and speed wrenches, should always be investigated
• The laws of motion economy - the use of the human body


  • Both hands should begin and end their basic divisions of accomplishment simultaneously and should not be idle at the same instant, except during rest periods
  • The motions made by the hands should be made symmetrically and simultaneously away from and toward the center of the body
  • Momentum, should assist workers wherever possible, and should be minimized if it must be overcome by muscular effort
  • Continuous curved motions are preferable to straight-line motions involving sudden and sharp changes in direction
  • The least number of basic divisions should be used: these should be confined to the lowest practicable classifications
  • Work done by the feet should be done simultaneously with work done by the hands
  • The middle finger and the thumb are the strongest working fingers
• The feet are not capable of efficiently operating pedals when the operator is in a standing position
• Location of tools and materials


  • So that ideal motion patterns can be arranged
• The Laws of Motion Economy


  • Work done by the feet should be done simultaneously with work done by the hands
  • Relieve the hands of work that can be done by the feet, but only if this work is performed while the hands are occupied
  • Foot pedal devices that allow clamping, parts ejection, or feeding can often be arranged, freeing the hands for other, more useful work and consequently reducing the cycle time
• Feet


  • Can be applying pressure to something, such as on a foot pedal
  • Difficult to operate a foot pedal while standing, which would mean maintaining the full body weight on the other foot
• Fingers


  • The middle finger and the thumb are the strongest working fingers
  • The index finger, fourth finger, and little finger are not capable of handling heavy loads over extended periods
  • Where a relatively heavy load is involved, it is usually more efficient to use the middle finger or a combination of the middle finger and the index finger
• Twisting motions


  • Should be performed with the elbows bent
  • When the elbow is extended, tendons and muscles in the arm are stretched, which can overstress muscle groups and tendons
• Gripping tools


  • Workers should use the segments of the fingers closest to the palm of the hand
  • The segments of the fingers closest to the palm are stronger than the other segments, and being closer to the load held in the hand, they do not induce as great a bending movement as do the more remote segments
• Fixed locations for all tools and material

  • Should be provided to permit the best sequence and to eliminate or reduce the therbligs search and select

  
• In driving an automobile, the brake pedal is in a fixed location


  No time is required to decide where the brake is located, the body responds instinctively
• If the location of the brake foot pedal varied from time to time

  Considerably more time would be needed to brake the car
• Providing fixed locations for all tools and materials at the workstation

  • Eliminates, or at least minimizes, the short hesitations required to search and select the various objects needed to do the work
• Gravity bins and drop delivery

  • Reduce reach and move times
  • Wherever possible, ejectors should remove finished parts automatically
• Utilizing gravity bins, components can be continuously brought to the normal work area

  • Eliminating long reaches to get these supplies
• Gravity chutes allow the disposal of completed parts within the normal area


  • Eliminating the necessity for long moves to do so
  • Making a clean work area possible, as finished material is carried away from the work area, rather than stacked up all around it
• All materials and tools should be located within the normal working area in both the vertical and the horizontal planes
• The greater the distance, the larger the muscular effort, control, and time. It is therefore important to minimize distances
• Normal working area


  • The most convenient zone within which motions may be made by that hand with a normal expenditure of energy
• Design facilities and workstations by considering such factors as arm reach, leg clearance, and body support, since these human dimensions are important criteria in developing a work environment that is comfortable and efficient
• Operator's working posture and workstation

  • An overall optimum working posture and workstation is shown in Figure 5.10
• Comfortable chair for the operator and the workstation's height

  • Should be so arranged that the work can be efficiently performed by the operator alternately standing or sitting
• Workplaces requiring the operator to stand a significant portion of the day are conducive to high fatigue
• Good chair design


  • Should permit several effective working postures