1. Overview

In mechanical design, a safety / guarding module is a function module that protects operators, maintenance personnel, surrounding equipment, and products from hazards inside a machine.

A machine contains various hazards, such as drive sections, rotating parts, reciprocating mechanisms, cutting sections, pressing sections, hot surfaces, electrical sections, pneumatic systems, and hydraulic systems. These hazards exist even during normal operation, and they can become more dangerous during non-routine tasks such as adjustment, cleaning, inspection, troubleshooting, and removal of jammed products.

The safety / guarding module eliminates these hazards, restricts access to them, detects hazardous conditions, stops the machine when necessary, and prevents workers from entering hazardous areas.

In other words, the safety / guarding module is the design area that controls risk and protects people inside a machine.

For example, safety covers, fixed guards, movable guards, interlock switches, emergency stop buttons, light curtains, safety mats, two-hand control devices, safety relays, safety PLCs, protective fences, transparent covers, anti-pinch structures, and fall-prevention devices may all be included in the safety / guarding module.

A safety / guarding module is not a cover that is added to the outside of the equipment at the end of design.
It directly affects machine operation, maintenance methods, cleaning methods, operator accessibility, productivity, legal requirements, and product reliability.

Therefore, the safety / guarding module should not be treated as a part added during the final stage of mechanical design. It should be reviewed together with the functional modules from the early design stage.

2. Definition

A safety / guarding module is a function module that identifies hazards in a mechanical system, restricts access to hazardous areas, detects hazardous states, and stops the machine in a safe state when necessary.

The core purpose of the safety / guarding module can be summarized as follows:

To protect people from machine hazards and ensure that the machine stops safely or maintains a safe state under hazardous conditions.

The safety / guarding module performs the following functions.

Safety / guarding is not simply “covering” a machine.
It is the design of the relationship between hazards and people.

3. Role in Mechanical Systems

The safety / guarding module performs the following roles within a mechanical system.

3.1 It Blocks Direct Access to Hazards

A machine has many areas that are dangerous if workers come into direct contact with them.

Typical hazards include the following.

The safety / guarding module creates physical or electrical protection structures so that people cannot directly access these hazards.

3.2 It Stops the Machine Under Hazardous Conditions

Not every hazard can be controlled by physical covers alone.
Some hazards require the system to detect operator access, cover opening, product jams, abnormal positions, overloads, or emergency situations and then stop the machine.

Safe stop may be required in the following cases:

• When a cover is opened

• When a worker approaches a hazardous area

• When an emergency stop button is pressed

• When a light curtain is interrupted

• When a safety mat is stepped on

• When a door interlock is released

• When an axis exceeds the allowable travel range

• When clamping is not completed

• When a product is jammed or in an abnormal position

• When overload or overpressure occurs

In these cases, simply stopping the motor command may not be sufficient.
Depending on the risk, power removal, brake operation, residual energy removal, and restart prevention must also be reviewed.

3.3 It Makes Human-Machine Interaction Safe

A machine is not used only during automatic operation.
Workers interact with the machine in many ways, including product loading, product removal, cleaning, adjustment, inspection, tool replacement, troubleshooting, jam removal, trial operation, and manual operation.

The safety / guarding module must consider these working situations.

Good safety design is not simply keeping workers away from the machine.
It enables workers to perform the tasks they actually need to do under safe conditions.

3.4 It Manages Hazardous Energy

Machine hazards do not come only from moving parts.
Energy itself can become a hazard, including electricity, pneumatic pressure, hydraulic pressure, gravity, heat, springs, rotational inertia, compressed air, and stored pressure.

Hazardous energy to review includes:

• Electrical energy

• Rotational inertia

• Pneumatic residual pressure

• Hydraulic residual pressure

• Gravity load

• Spring restoring force

• High-temperature thermal energy

• Stored elastic energy

• Vacuum holding force

• Internal pressure of pressure vessels

For example, even after an emergency stop is pressed, a vertical axis may descend due to gravity.
Even after a pneumatic valve is shut off, a clamp may move due to residual pressure inside the cylinder.
A rotating body may continue rotating by inertia even after power is removed.

Therefore, the safety / guarding module must consider the generation, storage, transfer, and release of hazardous energy.

3.5 It Protects Products and Equipment

The primary purpose of a safety / guarding module is to protect people, but it is also connected to equipment and product protection.

For example, if processing continues while a product is in an abnormal position, the tool may break.
If equipment operates while a cover is open, foreign matter or operator tools may enter the machine.
Without a guard, fragments or liquids may contaminate surrounding equipment.

The safety / guarding module provides the following protection functions:

• Prevention of product separation

• Prevention of tool breakage

• Prevention of contamination of surrounding equipment

• Prevention of fragment scattering

• Prevention of liquid splashing

• Prevention of product falling

• Prevention of foreign matter ingress

• Restriction of access to the inside of the equipment

• Prevention of abnormal operation

3.6 It Determines Productivity and Maintainability Together

If a safety structure is inconvenient, workers may try to bypass or remove the guard.
In that case, the purpose of safety design is lost.

Therefore, the safety / guarding module must consider not only safety, but also productivity and maintainability.

Elements to review include:

• Ease of opening and closing covers

• Cleaning accessibility

• Product changeover accessibility

• Tool replacement accessibility

• Inspection window or transparent cover

• Sensor adjustment accessibility

• Tool-less removal

• Cover weight and hinge structure

• Operator visibility

• Restart procedure

• Return procedure after interlock release

Safety design should not be only a “blocking design.”
It should be a design that allows necessary access safely and blocks hazardous access.

4. Main Types of Safety / Guarding Modules

Safety / guarding modules can be divided into several types according to the protection method.

5. Types of Safety / Guarding Methods

5.1 Fixed Guard Method

A fixed guard is a method that permanently covers or blocks a hazardous area using bolts, welding, fixed brackets, or similar structures.

Typical components include:

• Fixed cover

• Metal protective plate

• Mesh guard

• Chain cover

• Gear cover

• Belt cover

• Roller cover

• Fixed fence

Advantages

• The structure is simple.

• It reliably blocks direct access to hazards.

• It does not depend on the control system.

• Cost is relatively low.

• It is suitable for protecting rotating parts, chains, gears, and belts.

Points to Consider

• Maintenance accessibility may decrease.

• If disassembly is inconvenient, workers may remove it arbitrarily.

• Internal status may be difficult to check.

• Cleanability may decrease.

• Foreign matter may accumulate around bolted areas and gaps.

Design Review Points

• Range of hazard access prevention

• Guard stiffness

• Fastening method

• Need for removal

• Need for inspection window

• Cleaning accessibility

• Finger access distance

• Clearance between rotating part and cover

• Noise and vibration

• Cleanability when applied to food machinery

5.2 Movable Guard Method

A movable guard is a protective structure that can be opened when needed, such as a door, hinged cover, sliding cover, or removable cover.

Typical components include:

• Hinged door

• Sliding door

• Lift-up cover

• Removable cover

• Transparent cover

• Inspection door

• Quick-release cover

• Gas-spring-assisted cover

Advantages

• Maintenance and cleaning accessibility are good.

• Internal status is easy to check.

• Operator usability is good.

• It is advantageous for product changeover and tool replacement.

• It is easy to combine with interlocks.

Points to Consider

• Hazards must not occur while the cover is open.

• Cover weight and opening direction must be considered.

• Hinge and handle positions are important.

• Opening space is required.

• Wear and sagging caused by repeated opening and closing must be considered.

Design Review Points

• Opening direction

• Cover weight

• Hinge stiffness

• Handle position

• Open-hold structure

• Door sagging

• Interlock mounting position

• Cleaning accessibility

• Operator movement path

• Prevention of cleaning water ingress

5.3 Interlocked Guard Method

An interlocked guard stops the machine or limits hazardous motion when a cover or door is opened.

Typical components include:

• Safety door switch

• Door lock switch

• Key interlock

• Magnetic safety switch

• Hinged safety switch

• Safety relay

• Safety PLC

• Safety output shutoff circuit

Advantages

• Hazardous motion can be stopped automatically when the cover is opened.

• Maintenance accessibility and safety can be secured together.

• It can be applied to various automated machines.

• It is easy to connect with a safety control system.

• Restart conditions can be managed.

Points to Consider

• Switch position and operating method are important.

• The structure should not be easy to bypass.

• Residual energy may remain even after the cover is opened.

• The hazardous section must stop within a sufficiently short time.

• The system must transition to a safe state when a fault occurs.

Design Review Points

• Need for interlock

• Door switch type

• Need for door lock

• Hazardous section stop time

• Access time

• Anti-bypass structure

• Restart prevention

• Safety circuit configuration

• Maintenance mode

• Compatibility with washdown environments

5.4 Access Detection Method

The access detection method detects when a worker approaches a hazardous area and stops the machine.

Typical components include:

• Light curtain

• Safety laser scanner

• Safety mat

• Two-hand control device

• Rope switch

• Safety proximity sensor

• Area detection sensor

Advantages

• Access can be detected without a physical cover.

• It is suitable for equipment that requires product loading and unloading.

• Safety can be maintained while preserving worker accessibility.

• It is easy to apply to automated lines.

• A wide hazardous area can be monitored.

Points to Consider

• Safety distance calculation is required.

• If machine stop time is long, sufficient distance must be secured.

• Sensor performance may be affected by contamination, vibration, light, water, and reflection.

• The detection area must not be easy to bypass.

• Products or tools should not cause false detection.

Design Review Points

• Hazardous area size

• Access direction

• Stop time

• Safety distance

• Sensor detection height

• Possibility of bypass

• Interference with product flow

• Contamination environment

• Restart condition

• Inspection and test method

5.5 Emergency Stop Method

Emergency stop is a method that allows a worker to immediately stop the machine in a hazardous situation.

Typical components include:

• Emergency stop button

• Rope pull switch

• Emergency stop circuit

• Safety relay

• Safety PLC

• Power shutoff circuit

• Brake circuit

• Restart prevention circuit

Advantages

• Workers can respond immediately in hazardous situations.

• The entire machine or a specific zone can be stopped.

• It is an essential safety function in automated lines.

• It is relatively easy to install and recognize.

• Multiple devices can be installed around hazardous zones.

Points to Consider

• Emergency stop is not a preventive safety measure, but a last-response measure.

• It must be located where workers can easily access it.

• The machine must not restart automatically after it is pressed.

• Rotating parts or vertical axes may not stop immediately.

• Residual energy after stopping must be considered.

Design Review Points

• Button position

• Worker accessibility

• Stop range

• Stop method

• Restart prevention

• Indication and color

• Need for rope switch

• Whether the entire line stops

• Need for brake

• Reset procedure

5.6 Fall-Prevention Method

A fall-prevention method prevents vertical axes, lifters, heavy objects, or upper-mounted components from falling due to gravity.

Typical components include:

• Mechanical stopper

• Brake

• Ratchet structure

• Safety pin

• Counterbalance

• Check valve

• Rod-lock cylinder

• Fall-prevention clutch

• Safety support

Advantages

• Accidents involving vertical axes and heavy objects can be prevented.

• Safety is improved during power failure or air shutoff.

• Safe support conditions can be created during maintenance.

• It is essential for lifting equipment.

• Risk is reduced when workers access the equipment.

Points to Consider

• Drive stop and mechanical fall prevention must be reviewed separately.

• Brake capacity and response time are important.

• A physical support device may be required during maintenance.

• Falling due to single-component failure must be prevented.

• Regular inspection is required.

Design Review Points

• Vertical load

• Falling distance

• Brake capacity

• Mechanical stopper position

• Operation during power failure

• Operation during air shutoff

• Maintenance support method

• Need for redundant safety

• Inspection interval

• Manual release method

5.7 Flying-Object and Splash Prevention Method

This method prevents cutting chips, fragments, liquids, powders, or product pieces from flying outside the machine.

Typical components include:

• Transparent protective cover

• Chip cover

• Waterproof cover

• Flying-object prevention plate

• Impact-resistant window

• Liquid splash cover

• Enclosed cover

• Exhaust duct

Advantages

• It is effective for operator protection.

• Contamination of surrounding equipment is reduced.

• The working environment can be kept clean.

• It is suitable for cutting, cleaning, filling, and mixing processes.

• Protection can be provided while allowing internal status to be checked.

Points to Consider

• Impact resistance of the cover material is important.

• Transparent covers can be vulnerable to contamination and scratches.

• Internal pressure or liquid flow must be considered.

• Cleanability and drainability are required.

• Residue must not accumulate inside the cover.

Design Review Points

• Type of flying material

• Flying direction

• Cover material

• Transparency

• Impact resistance

• Waterproof performance

• Drainability

• Cleaning accessibility

• Replaceability

• Internal visibility

6. Main Design Criteria

The following criteria should be reviewed when designing a safety / guarding module.

6.1 Hazard Identification

The first task is to identify hazards inside the machine.

Review points include:

• Rotating sections

• Reciprocating sections

• Cutting sections

• Pressing sections

• Pinch points

• High-temperature sections

• Electrical sections

• Pneumatic / hydraulic sections

• Vertical axes

• Heavy objects

• Sharp edges

• Areas where fragments may fly

• High-speed transfer sections

• Areas accessed during maintenance

Hazards must be checked not only during automatic operation, but also during adjustment, cleaning, maintenance, and troubleshooting.

6.2 Accessibility

Even if a hazard exists, the risk level is lower if people cannot access it.
Conversely, even a small hazard becomes more serious if workers access it frequently.

Review points include:

• Can a worker put a hand into the area?

• Can a worker enter the area with the body?

• Can the hazard be reached with a tool?

• Is the area accessed during cleaning?

• Is the area accessed during jam removal?

• Is adjustment required with the cover open?

• Is access required during maintenance?

• How frequent is the access?

Safety design must review not only the hazard itself, but also accessibility to that hazard.

6.3 Stop Time and Safety Distance

When an access detection device is used, it takes time for the machine to actually stop.

Therefore, a safety distance must be secured so that the machine stops before the worker reaches the hazardous point.

Review points include:

• Sensor response time

• Safety circuit response time

• Drive section stop time

• Brake response time

• Distance to the hazardous point

• Worker approach speed

• Detection area height

• Possibility of bypass

• Restart condition

For equipment with a long stop time, simply installing a light curtain or safety scanner close to the hazard may not be sufficient.

6.4 Residual Energy

Hazardous energy may remain even after the machine stops.

Residual energy to review includes:

• Rotating body inertia

• Gravity load of vertical axes

• Pneumatic residual pressure

• Hydraulic residual pressure

• Spring compression force

• Heat in high-temperature sections

• Stored electrical energy

• Vacuum holding force

• Compressed product load

Structures are required to remove residual energy, maintain it safely, or indicate it to workers.

6.5 Restart Prevention

Automatic restart after a safe stop is dangerous.

Review points include:

• Need for manual reset after emergency stop

• Prevention of automatic restart after cover closure

• Prevention of automatic restart after power return

• Prevention of unexpected motion after air return

• Reset procedure after safe area recovery

• Lockout device during maintenance

• Operator confirmation procedure

The safety signal returning to normal and the machine being allowed to restart are different issues.

6.6 Guard Structure and Stiffness

A guard must have enough structural stiffness to protect workers from hazards.

Review points include:

• Cover material

• Cover thickness

• Frame stiffness

• Impact resistance

• Fixing method

• Hinge strength

• Locking device

• Possibility of deformation

• Finger access distance

• Gap size

• Sharp edges

If a guard is too weak, it may deform or fail due to impact, vibration, repeated opening and closing, or cleaning pressure.

6.7 Usability and Maintainability

A safety / guarding module must be easy to use so that it is actually maintained.

Review points include:

• Ease of opening and closing covers

• Cover weight

• Hinge position

• Handle position

• Inspection window

• Transparent cover

• Cleaning accessibility

• Tool replacement accessibility

• Sensor adjustment accessibility

• Component replacement space

• Cover storage location

• Possibility of tool-less disassembly

A guard with poor usability is likely to be bypassed or removed by workers.

6.8 Cleanability and Hygiene

In food machinery, the safety / guarding module is also part of hygienic design.

Review points include:

• Cleanability of guard surfaces

• Prevention of water accumulation

• Minimization of gaps and pockets

• Contamination management of transparent covers

• Prevention of residue inside covers

• Cleanability of hinges and handles

• Waterproofing of interlock switches

• Cleaning water drainage path

• Separation between food-contact and non-food-contact areas

• Ease of reassembly after cleaning

If a guard interferes with cleaning or traps residue, it becomes a problem in food machinery.

7. Interface with Other Modules

The safety / guarding module is connected to all function modules.

7.1 Relationship with the Drive Module

The drive module is a major hazard source because it creates motion and force.

Review points include:

• Are motor rotating sections exposed?

• Are couplings and shafts protected?

• Can the cylinder operating area be accessed?

• Does the drive section stop safely during emergency stop?

• Does hazardous motion not occur during power failure or air shutoff?

• Is a brake or safe stop function required?

7.2 Relationship with the Power Transmission Module

The power transmission module has a high risk of pinching and entanglement.

Review points include:

• Are gear mesh areas protected?

• Are chains and sprockets covered?

• Can a hand enter between belt and pulley?

• Are shaft ends and keyways exposed?

• Is rotating part stop time long?

• Can power be isolated during maintenance?

7.3 Relationship with the Motion / Positioning Module

The motion / positioning module includes moving bodies, sliders, tables, robots, and lifters, so there is a risk of collision and pinching.

Review points include:

• Can workers access the moving body path?

• Are there pinch points between the slider and frame?

• Is fall prevention provided for vertical axes?

• Is there access risk during homing?

• Is low-speed limitation required during manual operation?

• Are mechanical stoppers installed at travel ends?

7.4 Relationship with the Processing / Working Module

The processing / working module creates direct work hazards such as cutting, pressing, sealing, forming, and mixing.

7.5 Relationship with the Tooling Module

The tooling module is a high-risk area because it directly contacts the target object during work.

Review points include:

• Is the tool sharp?

• Is the tool hot?

• Does the tool rotate at high speed?

• Is there injury risk during tool replacement?

• Is a guard required around the tool access area?

• Can fragments fly out if the tool breaks?

• Can a safe state be maintained during tool cleaning?

7.6 Relationship with the Holding / Clamping Module

The holding / clamping module can create pinch hazards and unexpected motion hazards.

Review points include:

• Can a hand enter the clamping area?

• Is warning or detection required before clamping motion?

• Should work be prohibited before clamping is completed?

• Does the target object not fall during emergency stop?

• Does the clamp open or close during air shutoff?

• Does the product not fly out or fall during clamp release?

7.7 Relationship with the Structural Support Module

The safety / guarding module is mounted on the structural support module.

Review points include:

• Is the guard mounting section sufficiently stiff?

• Does the cover frame not vibrate?

• Is the interlock switch position stable?

• Is there space for cover opening and closing?

• Are inspection and cleaning accessibility secured?

• Does the machine structure make guard bypass difficult?

7.8 Relationship with the Control / Sensing Module

The safety / guarding module is closely connected to the control / sensing module.

Review points include:

• Are safety input signals connected to the control system?

• Do safety outputs actually remove power from the drive section?

• Are emergency stop and normal stop clearly separated?

• Are interlock signals protected from bypassing?

• Can safety sensor faults be detected?

• Are restart conditions clear?

• Are safety circuits separated from general control circuits?

8. Application in Food Machinery

In food machinery, the safety / guarding module is connected not only to operator protection but also to hygiene, cleanability, and prevention of foreign matter contamination.

Important conditions for safety / guarding modules in food machinery include the following.

In food machinery, a completely enclosed guard can reduce cleanability, while an overly open structure can reduce safety.
Therefore, balance between safety and cleanability is important.

Especially when raw material can enter inside the cover, the cover should be easy to open, clean, and reassemble while maintaining its safety function.

9. Common Design Mistakes

Common design mistakes in safety / guarding modules include the following.

9.1 Adding Guards at the End of Design

If guards are added at the end, interference, poor accessibility, cleanability problems, interlock position problems, and operator flow problems are likely to occur.

Safety / guarding should be designed together from the initial layout stage.

9.2 Assuming That a Cover Alone Makes the Machine Safe

Even with a cover, the machine is not safe if the hazardous section stop time is long, the cover opens easily, or residual energy remains after the cover is opened.

Guards must be reviewed together with physical isolation, safe stop, residual energy management, and restart prevention.

9.3 Designing Guards That Workers Are Likely to Bypass

If a cover is heavy, difficult to open, interferes with cleaning, or greatly increases product changeover time, workers may try to bypass it.

Safety design must be reviewed together with actual work flow.

9.4 Treating Emergency Stop as the Main Safety Measure

Emergency stop is a last-response measure used when an accident is about to occur.
Primary risk-prevention measures are hazard elimination, guards, interlocks, access detection, and securing safety distance.

Emergency stop should be understood as an auxiliary safety function.

9.5 Ignoring Residual Energy

Even after power is removed, rotating parts may continue to spin, vertical axes may descend, and pneumatic cylinders may move due to residual pressure.

Safety design must always review the energy that remains after stopping.

9.6 Ignoring Cleanability in Food Machinery

Even if a guard appears safe, it becomes a problem in food machinery if it is difficult to clean or if residue accumulates.

Guards for food machinery must consider safety, cleanability, drainability, corrosion resistance, and foreign matter prevention together.

10. Design Checklist

The following questions can be used when designing a safety / guarding module.

10.1 Hazard Review

• Are there rotating, reciprocating, cutting, or pressing sections?

• Are there pinch points or crushing points?

• Are there hot surfaces, electrical sections, or pneumatic / hydraulic sections?

• Is there a risk of flying objects, splashing, or falling?

• What are the hazards during cleaning, adjustment, and maintenance, in addition to automatic operation?

10.2 Accessibility Review

• Can a worker put a hand into the hazardous area?

• Does the worker access the hazardous area during product loading or removal?

• Is access to the hazardous area required during jam removal?

• Are there situations where the machine must operate with the cover open?

• How frequent is access, and how long does the task take?

10.3 Guard Structure Review

• Is a fixed guard appropriate, or is a movable guard required?

• Are cover stiffness and thickness sufficient?

• Are there gaps where fingers or hands can enter?

• Does the cover not vibrate or sag?

• Does the cover not interfere with cleaning and maintenance?

10.4 Safety Control Review

• Is an interlock required?

• Is a door lock required?

• Is the emergency stop button position appropriate?

• Is a light curtain or safety scanner required?

• Does the safety signal actually remove power from the drive section?

• Is there a restart prevention procedure?

10.5 Residual Energy Review

• Do rotating parts continue rotating after stop?

• Is there a possibility that a vertical axis may fall?

• Does pneumatic or hydraulic residual pressure remain?

• Can workers access hot surfaces before they cool sufficiently?

• Can energy be isolated and locked during maintenance?

10.6 Maintenance and Cleaning Review

• Can covers be opened and closed easily?

• Can the module be disassembled for cleaning?

• Does cleaning water not accumulate?

• Are interlocks and sensors protected from cleaning water?

• In food machinery, can residue, corrosion, and foreign matter contamination be prevented?

11. Summary

A safety / guarding module is a core function module that protects operators, maintenance personnel, equipment, and products from machine hazards.

This module may consist of fixed guards, movable guards, interlocked guards, emergency stop devices, light curtains, safety scanners, safety mats, fall-prevention devices, flying-object prevention covers, energy isolation devices, safety relays, and safety PLCs.

A safety / guarding module is not simply a cover that blocks hazardous areas.
It is a design area that integrates hazard identification, access restriction, safe stop, residual energy management, restart prevention, worker accessibility, maintainability, and cleanability.

When designing this module, hazards, accessibility, stop time, safety distance, residual energy, guard stiffness, interlocks, emergency stops, access detection, maintenance accessibility, cleanability, and hygiene must be reviewed together.

The safety / guarding module is also directly connected to the drive module, power transmission module, motion / positioning module, processing / working module, tooling module, holding / clamping module, structural support module, and control / sensing module.

In food machinery, not only safety but also cleanable structures, waterproof interlocks, residue prevention, drainability, and prevention of foreign matter contamination must be considered.

Therefore, the safety / guarding module should be understood not as an additional device attached to the outside of the equipment, but as a core design module that determines machine safety, reliability, operability, maintainability, and hygiene.