engineering

Machine guarding

Machine guarding is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Machine guarding rather than just read about it. In short: Machine guarding is a safety feature on or around manufacturing or other engineering equipment consisting of a shield or device covering hazardous areas of a machine to prevent contact with body parts or to control hazards like chips or sparks from exiting the machine. Machine guarding provides a means to protect humans from injury while working nearby or while operating equipment.

Key takeaways

Machine guarding belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Machine guarding to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Machine guarding from memory before moving on to harder problems.

Reference excerpt

Machine guarding is a safety feature on or around manufacturing or other engineering equipment consisting of a shield or device covering hazardous areas of a machine to prevent contact with body parts or to control hazards like chips or sparks from exiting the machine. Machine guarding provides a means to protect humans from injury while working nearby or while operating equipment. It is often the first line of defense to protect operators from injury while working on or around industrial machinery during normal operations. In the U.S., machine guarding is referred to in OSHA's CFR 1910.212; in the U.K., machinery safety is covered mainly by PUWER."

Point guarding

Point guarding refers to guarding of moving parts on a machine that present a hazard to the machine operator or others who may come in contact with the hazard. OSHA 1910.212(a)(2) requires these guards to be “affixed to the machine where possible." Specifics for the type and construction of the guard are determined by the proximity of the guard to the hazard, and the type of hazard. Point of Operation Guarding refers to guarding the area of the machine where the work is performed. Construction of the machine and the guarding should “prevent the operator from having any part of his/her body in the danger zone during the operating cycle.”

Fixed perimeter guarding

Perimeter or barrier guarding refers to a barrier placed around a work area where an automated piece of equipment-like a robotic arm-performs a function. This type of guarding is generally a wire partition system, but also can take the form of pressure sensitive mats or light curtains. Wire partition systems used as machine guards must be fixed in place either on the machine or around its perimeter. These guarding systems may be configured with various sizes of wire mesh, solid sheet metal, or clear polycarbonate panels. Use of these materials depends on the hazard being guarded and the distance between the hazard and the guard. Mesh opening size of the guard depends on the proximity of the guard to the hazard. If the guard is installed close to moving parts, the mesh openings must be smaller than if the guard is installed a greater distance away from the moving parts. Mesh opening sizes for specific distances from the hazard are defined in ANSI/RIA R15.06-2012. Solid barriers such as sheet metal or clear view polycarbonate can be used to shield the hazard as well as control sparks or liquids. Size of the barrier (height and width) must conform to ANSI/RIA R15.06-2012. Wire partition guards provide a means of access to the guarded equipment with doors, lift out sections, or other controlled openings.

Safety devices

Electrical interlocks or other devices tied into the equipment's control circuit are mounted on access points and are configured to stop equipment operations when opened. These access points should also incorporate hardware to comply with the OSHA lockout/tagout regulation 1910.147. Lockout-tagout (LOTO) is a safety procedure to ensure the proper shutdown and isolation of hazardous equipment. The primary goal of lockout-tagout (LOTO) is the absolute control of hazardous energy. The lockout/tagout hardware allows the operator or maintenance person to lock the equipment in the stopped state while performing duties in the hazardous area. Light curtain systems may be used alone or in conjunction with other guarding systems. The light curtain projects a field or beams of light between two points and, when the field is broken-at any point, the light curtain system interrupts the circuit it is wired into. These can be used in areas where an operator must interact with operating equipment to prevent movement of the equipment while the operator works a hazardous area.

Pressure sensitive mats that are wired into the equipment's control system can be placed in hazardous areas and be set to stop the equipment if stepped on. These devices can be used alone or in conjunction with other guarding devices, usually at operator interaction points.

Applications

Packaging Equipment or pallet wrappers have a moving load and an arm that stretches plastic wrap around the load. Typically a three sided wire partition guard is placed around the wrapper, and a light curtain controls access to the open side where the wrapper is accessed by a lift truck.

Robotic Welding Cells incorporate wire mesh fixed barriers outfitted with vinyl welding curtains and light curtains or pressure sensitive mats. The welding curtains mounted inside of the fixed barrier control exposure to welding flash, sparks and spatter from the welding operation. While the light curtain or pressure sensitive mats prevent welding operations while the operator is loading/unloading the weld fixtures.

Robotic Material Handling for pallet pack or de-palletizing could use any of the aforementioned guarding systems. Light curtains or pressure sensitive mats around the perimeter of the work area that stop the robot when an operator enters. Wire partition could be used around the work area with an interlocked gate which stops the robot when opened.

See also Material handling Material-handling equipment Occupational safety and health Pallet racking

Notes and references

External links

Essential safety barriers for automated robotic workcells (1:36 min. video) Material Handling Industry Occupational Safety and Health Administration. "Machine guarding". United States Department of Labor. Retrieved 12 October 2013. Protective Guarding Manufacturers Association (ProGMA)

Illustrations

Worked examples

Example 1 — a first encounter with Machine guarding

Start with the simplest possible case. Write down what Machine guarding claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Machine guarding before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Machine guarding ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Machine guarding

In research: Machine guarding appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Machine guarding in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Machine guarding is common in secondary-school and first-year university syllabi. It links to neighbouring topics Safety engineering, so understanding it makes those chapters shorter.
In everyday life: Look for Machine guarding outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Machine guarding in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Machine guarding means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Machine guarding out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Machine guarding in simple terms?

Why does Machine guarding matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Machine guarding?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Machine guarding.