5. WORKPLACE, JOB & PRODUCT DESIGN
5.1 Work Environment
5.1.3 Tools
(Source: McPhee, 2005 - reproduced with the permission)
Figure 5.4 – Functional Viewing Distances
e) Reach
Arm and leg reach should be based on the dimensions of the shortest user and taking into consideration the postural, task requirements and working position.
f) Access and Clearance
Space allowances for horizontal and vertical clearances and access to the workstation; access to machines and equipment used by operators and for maintenance personnel must be incorporated into the design of the work stations. These allowances must be based on the dimensions of the largest user.
Forces are generated from the human musculoskeletal system through the tool to the work piece and vice versa. Stresses arising from excessive forces and poor postures are frequently the result of poor tool design or inappropriate use. In some cases if a tool slips, breaks or looses purchase acute injuries can occur.
(Source: Stevenson, 1999 - reproduced with the permission)
Figure 5.5 – An example of improved hand tool design – bending the handle not the wrist
Tools are grasped in the hands and may be simple or may have controls.
Generally mobile equipment is larger and is activated by controls eg: handles, buttons, knobs that have to be gripped, moved or turned by the application of manual or pedal force. These linkages become part of what is called the user interface. In some cases the status of the equipment can be transmitted to the operator through a display of some kind.
a) Handles
Gripping characteristics such as handle shape, palmar or pinch grips, output required eg: power or precision work should be considered.
Tools should have handles that have the proper shape, thickness and length to prevent pressure on the soft tissues of the hands and to allow a good firm grasp. They should be free of sharp edges and pinch points.
Insulate contact surfaces to prevent electric shock, burns or the transmission of unwanted vibration. Use low voltage electrical power and double insulation where possible.
b) Forces
The forces required to grip tools during use should be minimal and prevent slippage particularly where gloves are required eg hot, dirty or clean work. The grip surface should be compressible, non-conductive to vibration, heat, cold and electricity. Flanges can be used to stop the hand slipping down the tool or to keep a heavy tool slipping out of the hands when being carried.
If the tool is required to deliver power then it should have a power grip handle design ie: the hand should be capable of gripping the tool with four fingers on one side of the handle and the thumb reaching around the other side locking on the index finger.
Where precision work is being required, the tool should have a handle that allows it to be gripped by the thumb and the first finger, or the thumb and the first and second fingers.
c) Design
All edges and corners of the tool and associated equipment should be rounded off and sharp, protruding elements avoided.
Tools should be designed so that they can be held and used with wrist and hand in the neutral position. Where the task requires large forces or has to be performed over extended periods, the tool should permit the arms and shoulders to be used.
Align the tool‟s centre of gravity with the grasping hand so the operator does not have to overcome rotational movement or tool torque.
Ensure that the transmission of noise and vibration is minimised. Guard all moving parts.
d) Type of Operation
Power operated tools should be used instead of muscle power where possible. Using a single finger to operate a power tool is not recommended especially where it is repetitive and/or is required for extended periods. While the majority of the population prefers to use the right hand tools should be designed so that they can be used with either hand.
e) Weight
Tool weight should be minimal. Where tools are heavy counterbalancing devices can reduce the weight. The tool should be easy to set down and pick up.
(Source: ASCC, 2007 - reproduced with the permission)
Figure 5.6 – Use of concrete saw requires application of high force and sustained awkward postures of back and neck
f) Controls
Detailed advice regarding the design of controls is covered in Section 5.2.4.
g) Mechanical Aids
Job aids need to be well designed for the purpose and readily accessible if they are to be used when they should. For instance lifting aids need to be compact, easy to move and use, stable and safe.
Storage is often a problem and this needs to be considered when purchasing. In some cases moveable lifting aids such as cranes and hoists can be installed overhead thereby overcoming storage problems.
Height adjustable benches and jigs need to be sufficiently adjustable to accommodate all users and work tasks. Anthropometric tables (ranges of people sizes) are often used to guide designers in this. Adjustments should be easy and quick to make from the working position.
Wheels on mobile equipment should be of sufficient diameter to enable them to be rolled over rough or uneven surfaces without undue force and without the risk of sudden uncontrolled movements.
Maintenance programs must ensure that job aids meet legislative requirements and function as the manufacturer advises.