Control and Display Design/Anthropometry

            This packet is intended for use in an introductory Statics course when the concept of the moment is introduced.  The procedures for extracting data from anthropometric charts dealing with static posture in workstation design are presented.  In the homework problem the students compute the moments for five sets of forces (weights) and distances (arm reaches).  Although the moments are found to be the same, the effects on shoulder muscle fatigue are different.

Time for presentation is estimated as 15-20 minutes.

Objectives:

1. To reinforce the concept of the moment, as presented in Statics, with a practical example related to the human body.
2. To use anthropometric data and the concept of the moment to introduce the students to the need to consider ergonomics in design.

This packet includes the following items.

·        Lecture material for the instructor

·        Overheads for use during the lecture

·        Handouts for the students

·        A homework problem

 Download the Control and Display Design Packet in a printable Adobe Acrobat Format (pdf).  This includes overheads in a ready to use format.

Homework problem solutions, exam problems, and exam solutions are available to qualified recipients. Send an email with request information to Dr. Donald Bloswick.

  Control and Display Design/Anthropometry Lecture Outline

I.    A bit about design (OVERHEAD 1)

A.     In design you develop something that meets a defined need.

B.     Often there are many acceptable options.

C.     Design is a major engineering (and curriculum) requirement.

D.     Distribute the homework problem and explain that it deals with a relatively simple workstation design problem.

II.                 The issue (OVERHEAD 2)

A.     Statics assumptions result in relatively simple, mostly linear equations that are not time-dependent.

B.     However, a design must be safe, and requires careful consideration of how People will interact with the product of the design.

C.     Ergonomics is the relationship between the worker and the work environment.

D.     Ergonomic factors often are non-linear and time-dependent.

E.      Bad ergonomic design can be costly because it can lead to accidents, injuries and inefficient operations.

III.   The design tools (OVERHEAD 3)

A.     Anthropometry is that part of ergonomics that deals with the dimensions of the human body.

B.     We use anthropometric data in design. (OVERHEAD 4)

i.    This chart and the next chart are based on data developed by Chaffin.

ii.    This chart shows the time for a young male who is holding a weight to reach significant shoulder muscle fatigue for different forward arm reach postures.

iii.   Show the students that you can enter the graph with a forward arm reach of 50 cm and a weight of 5 N (slightly more than 1 pound) to find that significant shoulder muscle fatigue would occur after about 5 minutes.

iv.   (OVERHEAD 5) This chart is similar except it considers different hand heights for the same forward arm reach position.

v.   Show that 50 cm forward arm reach on the first chart is the same as 30 cm up on the second chart.

A BIT ABOUT DESIGN

·     In design you develop something that meets a defined need.

·     Often there are many acceptable options.

·     Design is a major engineering requirement.

THE ISSUE

Statics:  Simple, mostly linear equations that are not time-dependent.

Ergonomics:

·     The relationship between the worker and the work environment.

·     Often non-linear and time-dependent.

Bad ergonomic design can be costly because it can lead to accidents, injuries and inefficient operations.

Anthropometry is that part of ergonomics that deals with the dimensions of the human body. 

We use anthropometric data in design.

  Overhead 4

Expected time to reach significant shoulder muscle fatigue for different forward arm reach postures (Chaffin, 1973).

Overhead 5

Expected time to reach significant shoulder muscle fatigue for various

arm elevation postures (Chaffin, 1973).

Lecture Handout
A BIT ABOUT DESIGN

·        In design you develop something that meets a defined need.

·        Often there are many acceptable options.

·        Design is a major engineering requirement.

THE ISSUE

Statics:  Simple, mostly linear equations that are not time-dependent.

Ergonomics:

·        The relationship between the worker and the work environment.

·        Often non-linear and time-dependent.

Bad ergonomic design can be costly because it can lead to accidents, injuries and inefficient operations.

Anthropometry is that part of ergonomics that deals with the dimensions of the human body. 

We use anthropometric data in design.

Expected time to reach significant shoulder muscle fatigue for different forward arm reach postures (Chaffin, 1973).

Expected time to reach significant shoulder muscle fatigue for various

arm elevation postures (Chaffin, 1973).

Statics safety homework design problem (moments/control and display design/ anthropometry)

Ergonomics is the study of the relationship between the worker and the work environment.  In Statics you are learning to determine the forces and moments that result from various equilibrium loading conditions.  The values you find often might allow direct comparison between alternatives when only the effects on inanimate structures are to be considered.  The situation is more complex when the ergonomic effects on the human body must be considered.  When humans are involved, improper design for holding loads may cause discomfort and ultimately result in safety issues.  An example is the design of workstations and conditions related to static posture (sitting still and holding a load).  Figures 1 and 2 show the effects of various loading conditions in terms of the time to significant shoulder muscle fatigue.  It will be helpful for you to understand the relationship between these figures.  Figure 1 shows a "young male" reaching forward 30, 40 and 50 cm at a seated hand height above the floor of 105 cm.  Figure 2 shows a "young male" reaching forward 50 cm with shoulder flexions (arm elevations) related to a surface 75 cm above the floor.  Note that the hand position 30 cm above the surface in Figure 2 corresponds to the hand position at a reach of 50 cm in Figure 1.  Both are a reach of 50 cm at a hand height above the floor of 105 cm.

Complete Table 1 using the concepts of Statics and the ergonomic considerations presented in Figures 1 and 2.  How would the results in Table 1 influence you in designing a workstation?

Table 1.  Statics and Ergonomics Computations

Weight          Arm Reach        Arm Elevation         Moment       Time to Fatigue

(N)                   (cm)                  (cm)^{note 1}              (N-cm)              (min)

        10.0                   30                      30                     300^{note 2}               14^{note 3}

          7.5                   40                      30

          6.0                   50                      30

          6.0                   50                        5

          6.0                   50                      50

¹ These are elevations above a 75 cm high surface as shown in Figure 2.  Therefore, an arm elevation of 30 cm is 105 cm above the floor.

² [weight (10.0 N)] x ["horizontal" arm reach (30 cm)] = moment (300 N-cm)

3 In Figure 1 the graph is entered with a weight of 10.0 N and a reach of 30 cm to obtain an average time of 14 minutes as shown on the graph in Figure 1.

Figure 1.  Expected time to reach significant shoulder muscle fatigue for different forward arm reach postures.  The elbow is unsupported.  The greater the reach, the shorter the endurance time. (Chaffin, 1973)

Figure 2.  Expected time to reach significant shoulder muscle fatigue for various shoulder flexion (arm elevation) postures.  The larger the shoulder flexion angle from the torso, the earlier fatigue will develop. (Chaffin, 1973)