PMTS+ Workspace Design

Work measurement

General process of determining the time required for a qualified worker to carry out a task at a defined level of performance (basis for standard time).

Work sampling (activity sampling)

Work measurement technique that estimates the proportion of time spent on different activities by making many random observations over time.

Time studies

Direct work measurement method where an analyst times cycles of a task (usually with a stopwatch) to determine the normal time and standard time.

Predetermined motion time systems (PMTS) / predetermined time systems (PTS)

Work measurement technique that breaks a job into basic human motions and uses pre-established time values for each motion to build the job time.

Standard data

Tables or databases of previously established normal times that can be reused to set times for similar elements in new tasks.

Time formulas

Equations that express task time as a function of key variables (e.g., distance, weight, quantity) so that standard times can be calculated for many cases.

Task analysis

Systematic breakdown of a job into its elements and motions to understand and improve method and to assign time values.

Predetermined motion time system (PMTS) definition

Database of basic motion elements with associated normal time values plus procedures to analyze manual tasks and establish standard times.

Assumption of independence and additivity (PMTS)

In PMTS, each motion element is assumed to be independent of others and times are additive—what happens before or after does not change each element’s time.

F. W. Taylor – Scientific Management

Early work in fractionalizing tasks and measuring sub-task times, providing a foundation for predetermined time systems.

F. B. Gilbreth – Therbligs

Introduced motion study and defined 17 basic motion elements called Therbligs using film analysis.

Therbligs

Gilbreth’s set of 17 fundamental motion elements used in motion study (e.g., search, find, grasp, transport loaded).

Motion Study (R. Thun, 1925 proposals)

Early proposals for a system of pre-determined times for human motions, preceding modern PTS systems.

Work-Factor (WF) system

One of the earliest commercial predetermined time systems; development began around 1934 and was published in 1945.

Methods Time Measurement (MTM)

Earliest widely used PTS (1948) based on frame‑by‑frame analysis of motion-picture films, providing times for basic motions.

MOST (Maynard Operation Sequence Technique)

A later, higher-level predetermined motion time system (published 1972) that uses motion sequence models instead of individual elemental motions.

Advantages of PTS/PMTS

Can be done before a job is physically set up, does not require workers or time studies, and avoids subjective performance ratings.

Disadvantages of PTS/PMTS

Can be tedious and time‑consuming to apply, requires training/certification, and may not always perfectly reflect real performance.

Methods Time Measurement (MTM-1)

The most detailed form of MTM that provides time values for very basic motions such as reach, move, grasp, and position.

Functional requirements

Workstation must enable required tasks to be carried out effectively.

Visibility requirements

Ensure operator can see displays, tools, and workpieces clearly.

Hearing requirements

Auditory cues must be perceivable in the workspace.

Clearances

Space allowances for operator movement, tools, knees, feet, etc.

Reach requirements

Distances that allow comfortable access to controls and work objects.

Population expectations

Design considerations accounting for user population variability.

Standardization

Using consistent component placements and workstation setup.

Psychosocial factors

Worker motivation, stress, satisfaction influencing design.

Environmental factors

Lighting, noise, temperature, humidity affecting human performance.

Maintainability

Ease with which workstation can be maintained.

Adjustability

Design that accommodates variability in users and tasks.

Workplace adjustments

Changes to work surface height, layout, orientation.

Worker position adjustments

Seat, footrest, armrest modifications to fit user needs.

Workpiece and tools adjustment

Modifying location or height of workpieces and tools.

Seated workstation

Work area designed for tasks performed in seated posture.

Standing workstation

Work area designed for tasks performed in standing posture.

Slackening of abdominal muscles

Potential negative result of prolonged poor sitting posture.

Zone of Convenient Reach (ZCR)

Area where objects can be reached without leaning forward. depends on:

1. Forward reach distance (𝑟)

2. Vertical distance (𝑑) between shoulder and work object

Formula is: ZCR²=r²-d²

Forward reach distance (r)

Horizontal distance the operator can comfortably reach.

Vertical distance (d)

Height difference between shoulder and work object.

Work surface height

Height of work surface relative to elbow height, depending on task.

RULE OF THUMB:

design working heights at 5-10 cm (2-4 in) below elbow height, unless task

involves fine manipulation and seeing requirements or force application

Importance principle

Most important components placed in optimal locations.

Sequence of use principle

Components used sequentially placed adjacent to each other.

Functional principle

Functionally related components grouped together.

Frequency of use principle

Frequently used components placed in easily accessible areas.

Link analysis

Method to determine optimal arrangement of components using sequential or functional links.

• A sequential link of 5 for A B means that component B has been used five times right after component A.

• A functional link reports the number of times a component is used per unit of time or a task cycle.

Manual material handling (MMH)

Tasks involving lifting, lowering, pushing, pulling, or carrying objects.

Epidemiological approach

Uses historical injury data to identify risk patterns.

Biomechanical approach

Evaluates forces and moments acting on the body during MMH. (Applicable

for tasks where the frequency is less than 4 lifts per min)

Psychophysical approach

Worker adjusts load until the task is ‘acceptable’ to perform.

MMH Research Approach: Physiological Approach

Assesses cardiovascular strain such as heart rate and oxygen consumption.

NIOSH Lifting Equation

Tool to determine recommended weight limits for lifting tasks. used for MANUAL, TWO-HANDED LIFTING.

not used when:

one handed lift, lifting while carrying/pushing/pulling, >8 hours

Recommended Weight Limit (RWL)

Computed weight limit based on multipliers affecting lift safety, RWL = (LC)(HM)(VM)(DM)(AM)(FM)(CM)

Lifting Index (LI)

Ratio of actual lift weight to RWL, indicating lifting risk. (L/RWL)

Action limit (AL)

Level at which lifting task is good (LI ≤ 1).

Maximum permissible limit (MPL)

Lifting condition requiring immediate redesign (LI ≥ 3).

Conditions of use (NIOSH LE)

Situations where NIOSH equation cannot be applied.

Static Strength Prediction Model

Compares joint load moments with population strength to estimate capability.

3DSSPP

Software used to evaluate static strength and posture under load.

Rapid Upper Limb Assessment (RULA)

Method to evaluate upper body ergonomic risk factors.

RULA score

Single number indicating level of musculoskeletal disorder risk. (1-2 is negligible risk, 6+ is very high risk)

RULA procedure

Steps to evaluate posture, force, and repetition risk factors.

Localized Musculoskeletal Discomfort (LMD)

Method using Borg CR-10 scale to assess discomfort by body region.

Borg CR-10 scale

Rating scale from 0–10 for perceived discomfort intensity.

Electro-goniometer

Device measuring joint angles during movement.

Motion capture systems

Tools like VICON capturing detailed posture and motion data.

Work methods design

Guidelines for reducing ergonomic risks through improved task methods.

Load Constant (LC)

Definition: Maximum load allowed under ideal lifting conditions.
Specifications:

• LC = 23 kg (51 lb)

• Constant value; does not change with task conditions.

Horizontal Multiplier (HM)

Definition: Effect of horizontal distance between hands and midpoint between ankles.
Specifications:

• Range: 0 ≤ HM ≤ 1.0

• H = horizontal distance (cm)

Condition	HM Value
H < 25 cm	HM = 1.0 (ideal)
H > 63 cm	HM = 0 (unacceptable)

General formula:
➡ HM = 25 / H

Vertical Multiplier (VM)

Definition: Effect of vertical height of hands at the start of the lift.
Specifications:

• Range: 0 ≤ VM ≤ 1.0

• V = vertical hand height (cm)

Condition	VM Value
V = 75 cm	VM = 1.0 (ideal)
V > 175 cm	VM = 0 (unacceptable)

General formula:
➡ VM = 1 − 0.003 × |V − 75|

Distance Multiplier (DM)

Definition: Effect of vertical travel distance of the load.
Specifications:

• Range: 0 ≤ DM ≤ 1.0

• D = vertical travel distance (cm)

Condition	DM Value
D < 25 cm	DM = 1.0
D > 175 cm	DM = 0

General formula:
➡ DM = 0.82 + (4.5 / D)
(Note: DM cannot exceed 1)

Asymmetric Multiplier (AM)

Definition: Effect of torso twisting during lift.
Specifications:

• Range: 0 ≤ AM ≤ 1.0

• A = asymmetry angle (degrees)

Condition	AM Value
A = 0°	AM = 1.0 (ideal)
A > 135°	AM = 0 (unacceptable)

General formula:
➡ AM = 1 − 0.0032 × A

Frequency Multiplier (FM)

Definition: Effect of lift frequency, duration, and vertical location.
Specifications:

• Range: 0 ≤ FM ≤ 1.0

• F = lifts/min (measured over 15 minutes)

Condition	FM Value
F > 15 lifts/min	FM = 0 (unacceptable)

General rule:
➡ FM is determined from NIOSH Table 3.15 (depends on frequency, duration, V)

Coupling Multiplier (CM)

Definition: Effectiveness of hand-to-object coupling (quality of grip).
Specifications:

• Range: 0 ≤ CM ≤ 1.0

• Based on Good / Fair / Poor coupling

• Also depends on whether V < 75 cm or V ≥ 75 cm

Coupling Quality	CM (general)
Good	Highest CM
Fair	Intermediate CM
Poor	Lowest CM

foot motion

motion like pressing the breaks

leg or foreleg motion

motion like like swinging your legs while on a swing

sidestep

Case 1: move one leg to the side

Case 2: move one leg to the side, then bring the other leg to it

bend

bow down without bending the knees

stoop

bend your knees so you can touch the floor

work area arrangements guidlines

Consider visual displays first in upper regions of the available space.

1. Locate critical displays first; 15 degrees around the NLS.

2. Then locate secondary displays ; 30 degrees around the NLS.

Consider controls next in the lower regions of the available space.

1. Locate primary controls first ; keep the elbows close to the body, minimizing

biomechanical loads and the chances for blocking the view of operation.

2. Locate secondary controls.