Mechanical Safety

- Introduction

- Movement of a machine can be dangerous

- Safety in the Operation of Robots

- Eye protective Eyewear

- Selection factors

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Dr. Edmund Cheung


Everybody using the Laboratory and Workshop facilities has a responsibility to keep them in proper working order and to maintain a safe working environment in the working area.

People working in Laboratory and Workshop should be considerate, have good working attitude and be self-disciplined.


Take care of the facilities being used by you.

Take care of other people working in the area with you.

Take care of your own life!


Any accident or mishap may damage equipment, cause injury or death.

It is important to prevent accident or mishap from happening when operating mechanical equipment.


There are general rules and guidelines for you to follow in the Laboratory and Workshop areas.

There are also operational manuals and specific rules for every mechanical equipment to be followed by users.

Always if you are in doubt, do not attempt to operate by yourself, call for help!


What makes mechanical equipment dangerous?

It is because of the Mechanical Movement and Forces.


When you are operating a machine or a mechanical apparatus, you should always adopt a defensive attitude and be aware of the source of danger or the likely outcome of each sequence of operation.


Movement of a machine can be dangerous

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You have to understand what kind of Forces and Mechanical Movement

you will be involved with while operating the equipment.

To this you need to understand the basic working principles of the equipment or the proper machining processes associated with that particular machine.

Static Force

If a support is not strong enough for the an object with increasing weights, it might collapse suddenly.


If the safety valve for a pressure vessel e.g. the storage tank of an air compressor, is not working, the pressure will build up to a point it suddenly cause the tank to explode.

Dynamic Force

The magnitude of some dynamic forces are constant but most of them change due to acceleration and deceleration. You should not enter the area covered by the mechanical movement of the equipment.


Mechanical vibration is undesirable. It is harmful to the health of the equipment as it may loosening some joints, create additional stresses or induce fatigue.Resonance is evenly more damaging as the amplitude of vibration explodes to a very large scale, causing the collapse of the equipment. If there is unusual vibration or noise caused by the mechanical movement, you should immediately stop the running of it and find out the cause.

Cutting Forces

In the operation of machine tools, forces arising from cutting are unavoidable. You should know before the operation the direction of these forces in order to clamp your workplace in a proper manner. Incorrect operation of the machine tools will cause abnormal behaviour of the machine tool and unusual forces to damage it or cause injury to the operator.


Machine tools operation involves with a lot of rotation of the cutting tools or the workplaces. The centrifugal forces of a suddenly broken grinding wheel while in operation cause the broken pieces to fly out in various directions. The torque in drilling may rotate the workplace and the clamping device if it is not securely bolted onto the machine table.



     Handling of hand tools

     Regular checking of compressed air systems and hydraulic systems


     Operation of power press and press brake

     Operation of laser machining centre

     Operation of ordinary machine tools: shaping, milling, turning, grinding, drilling etc.

     Operation of CNC machine tools

     Operation of robots.


Beware of the heat generated in machining.

Beware of the radiation generated and the possible toxic gases created during the operation of laser materials processing.


Safety in the Operation of Robots

1. Always follow the exact sequence of operation for power-up and power- down.

2. Always start arm motions at slow speed. Only when arm paths are fully defined and verified, then the speed may be increased.

3. Always be aware of obstacles on the arm paths, and the limits of its working range.

4. Never enter the working range of the arm during its operations, or when someone is programming it with the controller.

5. Never press "Arm Power Off" button while the robot is moving, except for emergency stop purposes.

6. Do not replace components or make adjustments to the interior of the robot while the electrical supply is still switched on.

7. Cables to any connection port must never be inserted or removed unless the power has been switched off from the robot.

8. When on manual free mode, make sure that when the appropriate joint switch is pressed, the arm is properly supported and prevented from free- swinging.


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Eye protective Eyewear

In general, laser protective eyewear should be selected to protect the eye against maximum exposure anticipated while still permitting the greatest amount of light to enter the eye for the purpose of seeing. It should be remembered that protective eyewear should not be the primary means of protection against radiation and the

use of engineering controls (such as enclosure of the laser beam path. election of shields, and installation of door interlock) is considered a far important and reliable safeguard than relying on protective eyewear.


Selection factors

- wavelength of the laser output

- potential of multi-wavelength operation

- optical density of eyewear at laser wavelength

- visible light transmission requirement

- capability of the front surface to produce a specular reflection

- field of view provided by eyewear

- availability of prescription lenses, or sufficient goggle frame size to permit wearing spectacles inside the goggle

- ventilation port to prevent fogging, if full-face fit

- provision of side-guards/shields for spectacles

- comfort and fitness

- effect upon colour vision

- absence of irreversible bleaching when filter exposed to high peak irradiances

- impact resistance

- maximum permissible exposure, radiant exposure or irradiance

- radiant exposure or irradiance and the corresponding time factor at which laser safety eyewear damage occurs (penetration), including transient bleaching


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