1. Overview

In mechanical design, a control / sensing module is a function module that detects machine status, makes decisions, and outputs commands so that equipment operates according to the intended sequence and conditions.

A machine does not operate correctly simply because motors, cylinders, frames, guides, and tools are assembled together.
A system is required to determine when each component should move, where it should stop, under what conditions the next operation should begin, and how the machine should stop or recover when an abnormal condition occurs.

The control / sensing module performs this role.

Sensors read the current state of the machine, the controller evaluates those signals, and output devices operate motors, valves, heaters, cylinders, lamps, alarms, and other components. The HMI allows operators to check equipment status and set operating conditions.

In other words, the control / sensing module is a design module that reads machine status, evaluates conditions, executes actions, and detects abnormalities.

For example, proximity sensors, photoelectric sensors, limit switches, encoders, pressure sensors, temperature sensors, flow sensors, load cells, vision sensors, PLCs, I/O modules, servo drives, inverters, relays, solenoid valves, HMIs, indicator lamps, buzzers, control panels, wiring, communication modules, alarm logic, and interlock logic may all be included in the control / sensing module.

The control / sensing module is applied not only to automated equipment, but also to manual equipment, semi-automated equipment, inspection equipment, food machinery, packaging machines, processing equipment, transfer systems, and assembly equipment.

Therefore, the control / sensing module is not an area where electrical components are simply added at the final stage.
The machine operating sequence, sensor positions, reference structures, safety conditions, maintenance conditions, and quality judgment criteria must be reviewed together from the early stage of mechanical design.

2. Definition

A control / sensing module is a function module that detects equipment status, product position, operation completion, working conditions, and abnormal conditions in a mechanical system, and controls equipment sequence, outputs, stops, alarms, and recovery conditions based on that information.

The core purpose of this module can be summarized as follows:

To detect machine status and control machine operation so that the machine operates reliably according to the intended conditions and sequence.

The control / sensing module performs the following functions.

The control / sensing module does not simply mean a control panel or a single sensor.
It is a system design area that includes sensors, controllers, output devices, wiring, communication, interfaces, control logic, diagnostic logic, operating conditions, and safety conditions.

3. Role in Mechanical Systems

The control / sensing module performs the following roles within a mechanical system.

3.1 It Creates the Machine Operating Sequence

A machine operates correctly only when multiple functional modules operate in the correct order.

For example, an automatic packaging machine may operate in the following sequence.

1. Confirm product input

2. Detect product position

3. Start transfer

4. Confirm arrival at the correct position

5. Operate clamp

6. Perform processing or packaging operation

7. Confirm operation completion

8. Release clamp

9. Discharge product

10. Wait for the next cycle

Creating this sequence is a core role of the control / sensing module.

Machine operation becomes unstable if it is controlled only by simple time delays.
At each step, the system must confirm whether the product is actually present, whether the axis has reached the target position, whether the cylinder has fully moved, whether pressure has been established, and whether the tool has returned to its home position.

Therefore, the control / sensing module organizes machine operation as a combination of sequence and conditions.

3.2 It Detects Machine Status

Control begins with detection.

Without sensors, the controller cannot know the current state of the equipment.
The system must then depend on visual confirmation by the operator, time-based estimation, or mechanical stoppers alone.

Typical conditions detected by the control / sensing module include the following.

The purpose of a sensor is not simply to receive a signal.
Its purpose is to allow the machine to judge its actual state.

3.3 It Confirms Operation Completion

In automated equipment, the important point is not merely giving a command, but confirming whether the command has actually been completed.

For example, even if the controller outputs a cylinder-forward command, it does not mean that the cylinder has actually reached the forward end.
The operation may not be completed if pneumatic pressure is insufficient, a product is jammed, a guide is worn, or the cylinder sensor is misaligned.

Typical operation completion conditions that must be confirmed include:

• Cylinder forward completion

• Cylinder return completion

• Axis arrival at target position

• Motor stop completion

• Clamp completion

• Pressure establishment

• Vacuum holding completion

• Product detection completion

• Tool return to home position

• Cover closed confirmation

• Discharge completion

The control / sensing module confirms these completion conditions before moving to the next operation.

Without completion confirmation, equipment becomes unstable, and product defects, collisions, pinching, tool breakage, and malfunction can occur.

3.4 It Manages Quality Conditions

The control / sensing module not only controls operation, but also manages product quality conditions.

Control elements related to quality include the following.

Machine quality is not determined by mechanical structure alone.
Quality stability changes depending on where and what the sensors detect, what criteria the controller uses for judgment, and how abnormal conditions are handled.

3.5 It Detects Abnormal Conditions and Protects the Machine

A machine does not always operate only under normal conditions.

Products may become jammed, pneumatic pressure may be insufficient, sensors may become contaminated, an axis may fail to return to its home position, a heater may overheat, or an operation request may be made while a cover is open.

The control / sensing module must detect these abnormal conditions and protect the equipment.

Typical abnormal conditions include:

• No product

• Product jam

• Incorrect product position

• Cylinder operation timeout

• Axis position mismatch

• Sensor signal mismatch

• Low pressure

• Insufficient vacuum

• Overcurrent

• Overload

• Overheating

• Cover open

• Interlock released

• Communication error

• Homing failure

• Discharge failure

When an abnormal condition is detected, the equipment must perform actions such as stopping, slowing down, warning, retrying, discharging, displaying an alarm, or supporting manual recovery depending on the situation.

Good control design does not define only normal operation.
It also defines how the equipment stops safely and recovers under abnormal conditions.

3.6 It Creates the Interface Between Operators and Equipment

The control / sensing module provides an interface that allows operators to understand and operate the equipment.

The operator interface includes the following elements.

• Start button

• Stop button

• Emergency stop button

• Manual / automatic mode selection

• HMI screen

• Setting value input

• Alarm display

• Status indicator lamp

• Buzzer

• Production count display

• Error history

• Maintenance mode

• Manual operation screen

Even if a machine operates with high precision, field operability becomes poor if operators cannot understand the current state, cannot identify the alarm cause, or do not know the recovery procedure.

Therefore, the control / sensing module must provide information so that operators can operate the equipment safely and consistently.

4. Main Types of Control / Sensing Modules

Control / sensing modules can be divided into several types according to function and application area.

5. Types of Control / Sensing Design Methods

5.1 Sensor-Based Status Detection Design

Sensor-based status detection design detects the status of products, components, axes, cylinders, covers, pressure, temperature, and similar conditions.

Typical components include:

• Proximity sensor

• Photoelectric sensor

• Limit switch

• Reed switch

• Encoder

• Pressure sensor

• Vacuum sensor

• Temperature sensor

• Load cell

• Vision sensor

Advantages

• Machine status can be confirmed objectively.

• Operation completion can be judged.

• Product presence and position can be detected.

• Abnormal conditions can be detected early.

• Automatic operation becomes more stable.

Points to Consider

• Sensor position must match the actual detection target.

• Dust, water, oil, vibration, and temperature effects must be considered.

• Detection performance may vary depending on product color, material, and reflectivity.

• Sensor bracket stiffness and position repeatability are required.

• Sensor contamination and false detection must be considered.

Design Review Points

• Detection target

• Detection distance

• Detection direction

• Sensor type

• Installation position

• Adjustability

• Possibility of contamination

• Effect of cleaning water

• Cable protection

• Replacement accessibility

5.2 PLC-Based Sequence Control Design

PLC-based sequence control design controls the machine operating sequence based on input signals and operating conditions.

Typical components include:

• PLC

• Input module

• Output module

• Relay

• Timer

• Counter

• Solenoid valve

• Motor control output

• HMI interface

Advantages

• Machine operation sequence can be clearly organized.

• Input and output conditions can be logically managed.

• Automatic operation, manual operation, and maintenance mode can be separated.

• Alarm and recovery conditions can be systematized.

• Equipment modification and improvement can be handled more easily.

Points to Consider

• The machine operation sequence must be clearly defined.

• Sensor inputs must correspond to actual machine status.

• Missing conditions can cause malfunction.

• Manual operation conditions and automatic operation conditions must be separated.

• Safety-related control may not be appropriate to handle only with general PLC logic.

Design Review Points

• Operating sequence

• Input conditions

• Output conditions

• Completion conditions

• Timeout conditions

• Manual operation conditions

• Automatic operation conditions

• Alarm conditions

• Recovery conditions

• Separation from safety control

5.3 Position Feedback Control Design

Position feedback control design controls axis position, speed, acceleration, deceleration, and repeat position.

Typical components include:

• Servo motor

• Servo drive

• Encoder

• Stepper motor

• Home sensor

• Limit sensor

• Linear scale

• Position controller

Advantages

• Precise position control is possible.

• Repeat positioning accuracy can be improved.

• Speed, acceleration, and deceleration can be controlled.

• Position abnormalities can be detected.

• Multiple axes can be synchronized.

Points to Consider

• Machine stiffness and backlash affect position accuracy.

• The homing reference must be clear.

• Limit positions and safety margins are required.

• The relationship between encoder signal and actual machine position must be reviewed.

• Stop position and collision possibility must be reviewed together.

Design Review Points

• Required position accuracy

• Repeat positioning accuracy

• Travel distance

• Speed, acceleration, and deceleration

• Home reference

• Limit position

• Backlash

• Machine stiffness

• Need for position compensation

• Position abnormality alarm

5.4 Interlock Control Design

Interlock control design prohibits or restricts equipment operation when specific conditions are not satisfied.

Typical components include:

• Door sensor

• Cover sensor

• Cylinder completion sensor

• Clamp completion sensor

• Product position sensor

• Pressure confirmation sensor

• Temperature reached confirmation

• Safety relay interface

• PLC condition logic

Advantages

• Malfunction and collision can be prevented.

• Operation sequence can be stabilized.

• Product defects can be reduced.

• Operator safety can be improved.

• Equipment damage under abnormal conditions can be reduced.

Points to Consider

• Too few interlock conditions can be dangerous, while too many can reduce operability.

• The behavior when a sensor fails must be defined.

• Necessary interlocks should remain active even in manual operation.

• Safety interlocks and general operation interlocks must be distinguished.

• Restart conditions after interlock release must be clear.

Design Review Points

• Operation prohibition conditions

• Operation permission conditions

• Sensor reliability

• Possibility of bypassing

• Manual operation conditions

• Safety circuit interface

• Error display

• Recovery procedure

• Restart conditions

• Maintenance mode conditions

5.5 HMI and Operator Interface Design

HMI and operator interface design provides information so that operators can operate the equipment and understand its status.

Typical components include:

• HMI screen

• Start button

• Stop button

• Manual / automatic mode switch

• Status indicator lamp

• Buzzer

• Production count display

• Alarm screen

• Setting value input screen

• Maintenance screen

Advantages

• Operators can easily understand equipment status.

• Setting values and operating conditions can be managed.

• Alarm causes and recovery procedures can be displayed.

• Manual operation and maintenance work can be supported.

• Production information and error history can be managed.

Points to Consider

• If the screen structure is too complex, field usability decreases.

• Alarm messages are not helpful if they are not specific.

• Incorrect setting value input must be prevented.

• Operator authority and administrator authority may need to be separated.

• Operability must be considered in washing, dust, and vibration environments.

Design Review Points

• Status to display

• Values to set

• Operator operation sequence

• Alarm messages

• Recovery guidance

• Manual operation screen

• Authority management

• Screen language

• Button location

• Prevention of incorrect input

5.6 Diagnosis and Alarm Design

Diagnosis and alarm design detects equipment abnormalities and provides information so that operators can identify the cause and recover the equipment.

Typical components include:

• Alarm code

• Error message

• Error history

• Sensor status display

• I/O monitor

• Timeout alarm

• Pressure abnormality alarm

• Temperature abnormality alarm

• Position abnormality alarm

• Communication error alarm

Advantages

• Failure diagnosis time is reduced.

• Maintenance work becomes easier.

• Repeated failures can be analyzed.

• Operator response can be standardized.

• Unnecessary part replacement can be reduced.

Points to Consider

• If there are too many alarms, operators may have difficulty distinguishing importance.

• If alarm messages are vague, field response becomes slow.

• If the displayed cause differs from the actual cause, reliability decreases.

• Temporary false detection and actual abnormalities must be distinguished.

• Alarm reset conditions must be clear.

Design Review Points

• Alarm target

• Alarm priority

• Alarm message

• Cause display

• Corrective action display

• Error history storage

• Sensor status display

• Recovery conditions

• Repeated alarm analysis

• Maintenance support

6. Main Design Criteria

The following criteria should be reviewed when designing a control / sensing module.

6.1 Clarity of the Detection Target

Before installing sensors, it must be clear what needs to be detected.

Review points include:

• Is product presence being detected?

• Is product position being detected?

• Is axis position being detected?

• Is operation completion being detected?

• Are pressure or temperature being detected?

• Is an abnormal condition being detected?

• Is a safety condition being detected?

• Is a quality condition being detected?

If the detection purpose is not clear, the number of sensors may increase, but control quality will not improve.

6.2 Sensor Position and Mechanical References

Sensor position must be connected to mechanical references.

Review points include:

• Is the sensor aligned with the actual detection target?

• Is the sensor bracket sufficiently stiff?

• Can the sensor position be adjusted?

• Is the sensor fixed securely after adjustment?

• Does vibration change the sensor position?

• Is the position maintained after cleaning or maintenance?

• Can the sensor be adjusted when the product changes?

• Is the position reproduced after sensor replacement?

Even if a sensor has good performance, detection reliability becomes low if the installation position is unstable.

6.3 Signal Reliability

Because the control system makes decisions based on sensor signals, signal reliability is important.

Review points include:

• Is the signal stable?

• Is there any noise influence?

• Are cable length and wiring route appropriate?

• Are grounding and shielding required?

• Is false detection possible?

• Does sensor contamination change the signal?

• Does vibration cause signal fluctuation?

• Must contact chattering or momentary signals be processed?

Unstable signals can lead to machine stoppage, malfunction, excessive alarms, and product defects.

6.4 Control Sequence and Conditions

The control sequence is the logic of machine operation.

Review points include:

• What is the start condition of each operation?

• What is the completion condition of each operation?

• What condition allows transition to the next operation?

• What is the operation failure condition?

• What is the timeout condition?

• What is the manual operation condition?

• What is the recovery condition after stop?

• What is the homing condition?

If the control sequence is not clear, the equipment will not operate reliably even if the mechanical structure is good.

6.5 Response Time and Synchronization

In some machines, sensor response time and output response time are very important.

Review points include:

• Sensor response speed

• PLC scan time

• Communication delay

• Servo response time

• Valve response time

• Cylinder operation time

• Detection position during high-speed transfer

• Encoder synchronization

• Product spacing

• Cycle time

In high-speed equipment, if sensor position and response time do not match, the machine may miss products, lose timing, or generate defects.

6.6 Manual Operation and Maintenance Operation

If only automatic operation is considered, actual field operation becomes difficult.

Review points include:

• Can each axis be moved manually?

• Can cylinders be operated individually?

• Are safety conditions maintained during manual operation?

• Can homing be guided manually?

• Can the machine recover after product jam removal?

• Are speed and output limited in maintenance mode?

• Can the operator check the current status?

Manual operation is not merely an auxiliary function.
It is an essential function for installation, adjustment, maintenance, and recovery.

6.7 Separation of Safety Control and General Control

General operation control and safety control must be separated.

Review points include:

• Is the emergency stop circuit separated from normal stop?

• Is the door interlock connected to the safety circuit?

• Are hazardous motions restricted by safety conditions?

• Are safety inputs and general inputs separated?

• Do safety outputs actually remove power?

• Is there a restart prevention condition?

• Does the system transition to a safe state when the safety circuit fails?

General PLC logic is suitable for equipment operation, but safety functions that protect people may require separate safety design.

6.8 Maintainability and Replaceability

The control / sensing module must be maintainable.

Review points include:

• Can sensors be replaced easily?

• Are cable connectors accessible?

• Can sensor status indicators be seen?

• Can I/O status be checked?

• Is the inside of the control panel accessible?

• Are wiring numbers and labels provided?

• Is adjustment easy after sensor replacement?

• Can spare parts be managed?

Sensors and control components can fail, so replaceability and diagnostic capability must be considered.

7. Interface with Other Modules

The control / sensing module is directly connected to all functional modules.

7.1 Relationship with the Drive Module

The drive module operates by control outputs.

Review points include:

• How are motor start and stop controlled?

• What signals are exchanged between the servo drive and PLC?

• How is cylinder forward / return completion confirmed?

• Is brake control required?

• Are overload and overcurrent detected?

• Are manual operation conditions defined?

7.2 Relationship with the Power Transmission Module

The condition of the power transmission module affects sensing and diagnostics.

Review points include:

• Is belt breakage or slipping detected?

• Can abnormal chain tension be checked?

• Can coupling looseness be detected through vibration or position error?

• Does ball screw backlash affect position control?

• Is rotating-section speed detection required?

• Can insufficient lubrication be managed by alarm?

7.3 Relationship with the Motion / Positioning Module

The motion / positioning module is one of the most closely connected modules to the control / sensing module.

Review points include:

• Is the home sensor position appropriate?

• Is a limit sensor required?

• Is position feedback required?

• Do mechanical stoppers and sensor positions interfere with each other?

• Can sensors confirm positional repeatability?

• Are manual movement and automatic movement conditions separated?

7.4 Relationship with the Processing / Working Module

The processing / working module is directly connected to quality conditions.

Review points include:

• What is the processing start condition?

• What is the processing completion condition?

• Are temperature, pressure, time, and position controlled?

• Is processing prohibited if the product is not in the correct position?

• Is abnormality in the working section detected?

• Can defective products be separated?

7.5 Relationship with the Tooling Module

The tooling module often requires sensors and control references.

Review points include:

• Is tool mounting status confirmed?

• Is tool position detected?

• Is tool wear detected or managed?

• Is the reference position maintained after tool replacement?

• Is an alarm possible when tool breakage occurs?

• Is return to the home position confirmed after tool cleaning?

7.6 Relationship with the Holding / Clamping Module

The holding / clamping module must confirm product holding status.

Review points include:

• Is clamp completion detected?

• Is clamp pressure confirmed?

• Is the product properly fixed?

• Is the next operation prohibited when clamping is incomplete?

• Is product drop detected or prevented when air pressure decreases?

• Is discharge completion confirmed after clamp release?

7.7 Relationship with the Hygienic / Cleanability Module

In food machinery, the control / sensing module must also consider hygiene and cleanability.

Review points include:

• Are sensors and cables protected from cleaning water?

• Does residue not accumulate around sensor brackets?

• Are electrical components not located above product-contact areas?

• Does sensor position remain unchanged after cleaning?

• Are waterproof connectors required?

• Is a cleaning mode required?

7.8 Relationship with the Safety / Guarding Module

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

Review points include:

• Is the door interlock signal connected to the safety circuit?

• Does the emergency stop signal actually remove power?

• Which motions are prohibited when the cover is open?

• Is safety sensor failure detected?

• Are restart conditions clear after safe stop?

• Are the safety circuit and general control circuit separated?

7.9 Relationship with the Maintenance / Serviceability Module

The control / sensing module is directly connected to serviceability.

Review points include:

• Is sensor replacement easy?

• Can I/O status be checked in the field?

• Is alarm history stored?

• Is there a manual operation screen?

• Is the homing procedure clear?

• Are safety conditions maintained in maintenance mode?

8. Application in Food Machinery

In food machinery, the control / sensing module must be reviewed together with hygiene, cleanability, foreign matter prevention, and safety, not only productivity.

Important conditions for control / sensing modules in food machinery include the following.

In food machinery, sensors are not used only to confirm machine operation.
They are directly connected to product quality and food safety, including product presence, filling quantity, sealing temperature, cleaning completion, cover closed status, pressure conditions, and foreign matter inspection.

Therefore, the control / sensing module in food machinery must consider waterproofing, cleanability, detection reliability, product contamination prevention, safety conditions, and data management together.

9. Common Design Mistakes

Common design mistakes in control / sensing modules include the following.

9.1 Assuming Sensors Can Be Added Later

If sensors are added after the machine structure is completed, the detection position may be poor, brackets may be weak, adjustment may be difficult, or cable routing may be unfavorable.

Sensor positions should be determined from the early mechanical design stage together with mechanical reference surfaces, detection targets, and maintenance accessibility.

9.2 Relying Too Much on Time-Based Control

If the next operation is executed based on the assumption that a cylinder will arrive after one second, malfunction can occur when pressure drops or a product jam occurs.

Important operations should be controlled based on actual completion signals rather than time alone.

9.3 Ignoring Sensor Bracket Stiffness

Even if the sensor itself is precise, its position changes if the bracket is weak due to vibration or impact.

A sensor bracket is not merely an auxiliary part.
It is a mechanical element that determines detection reliability.

9.4 Using Vague Alarm Messages

If only messages such as “Error,” “Fault,” or “Sensor NG” are displayed, operators cannot quickly identify the cause.

Alarms should indicate which section failed to satisfy which condition within what time.

9.5 Not Considering Manual Operation Conditions Enough

Many machines operate well in automatic mode but are difficult to recover, adjust, home, or troubleshoot when a product jam occurs.

Manual operation and maintenance operation should be included from the initial control design stage.

9.6 Confusing Safety Control with General Control

Handling emergency stops or door interlocks only with general PLC logic may not be sufficient depending on the risk level.

Functions directly related to human safety may require separate review of safety circuits, safety relays, safety PLCs, and safety drive functions.

10. Design Checklist

The following questions can be used when designing a control / sensing module.

10.1 Detection Target Review

• What needs to be detected?

• Which is important: product presence, position, orientation, or completion status?

• Does the sensor accurately represent the actual machine state?

• Are unnecessary items being detected excessively?

• What detection is required for quality conditions and safety conditions?

10.2 Sensor Installation Review

• Is the sensor position aligned with the detection target?

• Is the sensor bracket sufficiently stiff?

• Can the sensor be adjusted and replaced?

• Is it protected from contamination, water, dust, oil, and vibration?

• Are cable protection and wiring route appropriate?

10.3 Control Sequence Review

• Is the start condition of each operation clear?

• Is the completion condition of each operation clear?

• Are failure conditions and timeout conditions defined?

• Are recovery conditions after stop defined?

• Are manual operation and automatic operation conditions separated?

10.4 Output Control Review

• Which devices are controlled as outputs?

• Are operating conditions for motors, valves, heaters, and brakes clear?

• Is completion confirmation provided after output?

• Does an alarm occur when output fails?

• Are safety conditions maintained during manual output operation?

10.5 Alarm and Diagnosis Review

• Which conditions should be treated as alarms?

• Are alarm messages specific?

• Can the operator identify the cause?

• Is alarm history stored?

• Are alarm reset and recovery conditions clear?

10.6 Safety Integration Review

• Are emergency stop and normal stop separated?

• Are door interlocks and safety sensors properly connected?

• Is automatic restart prevented after safety conditions are released?

• Are safety circuits and general control circuits separated?

• Are necessary safety conditions maintained in maintenance mode?

11. Summary

A control / sensing module is a core function module that detects machine status, evaluates conditions, and enables equipment to operate according to the intended sequence and conditions.

This module may consist of proximity sensors, photoelectric sensors, limit switches, encoders, pressure sensors, temperature sensors, load cells, vision sensors, PLCs, I/O modules, servo drives, inverters, solenoid valves, HMIs, alarm logic, interlock logic, communication modules, control panels, and wiring structures.

A control / sensing module is not simply a matter of installing sensors and connecting a PLC.
It is a design area that reviews detection targets, sensor positions, mechanical references, input reliability, control sequence, output conditions, interlocks, feedback, alarms, manual operation, maintenance operation, safety control, and operator interface together.

When designing this module, detection purpose, sensor installation conditions, signal stability, control sequence, operation completion conditions, response time, manual operation conditions, separation of safety control, maintainability, and replaceability must be reviewed comprehensively.

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

In food machinery, the control / sensing module must be reviewed together with product quality, hygiene, cleanability, foreign matter prevention, safety conditions, and data management.

Therefore, the control / sensing module should be understood not as an additional element for adding electrical components to a machine, but as a core design module that determines machine operating logic, quality stability, safety, maintainability, and productivity.