1. Definition of Control Basis

Control Basis refers to the fundamental principles, design scope, decision criteria, and implementation structure that must be defined before designing the control system of general machinery.

Control is not simply the task of connecting devices such as motors, cylinders, sensors, and PLCs. It is the overall system design that converts required machine functions into executable commands, verifies the actual machine state, and adjusts, stops, or recovers operation when the machine deviates from normal conditions.

Control Basis must answer the following questions:

• What must be controlled?

• What is the purpose of control?

• How should the machine state be defined?

• Under what conditions should operation be permitted or prohibited?

• How should differences between the target state and the actual state be handled?

• What state should the machine enter when an abnormal condition occurs?

• Through what hardware and software architecture should the control functions be implemented?

• How can the same control performance be reproduced during assembly, manufacturing, and testing?

Control Basis is therefore not an explanation of individual control functions. It is the common foundation that all control design must follow.

2. Position of Control in Machine Design

The design process of general machinery generally follows this sequence:

Requirements → Function → Structure → Mechanism and Motion → Control → Assembly → Manufacturing → Validation

Each area has the following role:

Control converts the motion defined in Mechanism & Motion into actual machine operation.

If a mechanism defines “how the machine moves,” Control defines:

• When it should move

• Under what conditions it should move

• At what position and speed it should move

• How completion of the motion should be verified

• How the machine should respond when the command and actual result differ

• How the machine should stop under hazardous or uncertain conditions

Control is the connecting domain that completes the mechanical structure as an operable system.

3. Fundamental Purposes of Control

Control in general machinery has five primary purposes.

3.1 Function Execution

The machine performs the required process and work in the specified sequence.

Examples:

• Product feeding

• Positioning

• Clamping

• Cutting

• Forming

• Inspection

• Discharge

3.2 State Verification

The system verifies whether the commanded operation has actually been completed.

Examples:

• Has the product arrived?

• Has the cylinder reached the forward-completion position?

• Has the rotating element stopped?

• Has the set temperature been reached?

• Has the required clamping force been secured?

3.3 Operation Regulation

The system adjusts output to reduce the difference between the target value and the actual value.

Examples:

• Position correction

• Speed regulation

• Pressing-force maintenance

• Temperature regulation

• Pressure regulation

3.4 Operation Restriction

The system does not permit operation when the required conditions are not satisfied.

Examples:

• Machining prohibited before clamping is complete

• Automatic operation prohibited before homing is complete

• Spindle operation prohibited when lubrication pressure is insufficient

• Hazardous motion prohibited while a safety door is open

3.5 Fault Response and Recovery

When the machine leaves normal conditions, the system detects the abnormality and returns the machine to a safe and verifiable state.

Examples:

• Timeout

• Position mismatch

• Product jamming

• Overload

• Sensor inconsistency

• Loss of electrical power or pneumatic supply

4. Fundamental Elements of Control

Control is not a list of devices. It is composed of relationships among the following elements.

4.1 Command

A command defines what the machine is instructed to perform.

• Move

• Rotate

• Stop

• Press

• Clamp

• Heat

• Cool

• Feed

• Discharge

• Return

A command should include the target state rather than merely an output ON/OFF condition.

Examples:

• Not “Servo ON,” but “Move the working axis to the 250 mm position”

• Not “Cylinder forward,” but “Clamp the product at the working position”

• Not “Heater ON,” but “Maintain the chamber temperature at 80°C”

4.2 State

A state represents the machine’s current condition.

• Power condition

• Operating mode

• Axis position

• Device operating condition

• Product position

• Process progress

• Fault condition

• Safety condition

States form the basis for control decisions.

4.3 Condition

A condition defines the criteria used to determine whether an operation should start, continue, finish, or stop.

• Start condition

• Permissive condition

• Completion condition

• Transition condition

• Stop condition

• Retry condition

• Recovery condition

• Restart condition

4.4 Signal

A signal provides information about the actual machine condition to the control system.

• Digital input

• Analog input

• Encoder signal

• Communication data

• Diagnostic information

• Safety signal

4.5 Response

A response defines how the machine reacts to a specific state or condition.

• Output adjustment

• Speed limitation

• Operation hold

• Retry

• Alarm generation

• Normal stop

• Fault stop

• Safety stop

• Emergency stop

• Operator intervention request

Control must clearly connect these five elements.

Command → State → Condition → Signal → Response

5. Definition of Control Targets

The first step in control design is to clearly define what must be controlled.

5.1 Motion-Related Control Targets

• Position

• Travel distance

• Rotation angle

• Speed

• Acceleration

• Deceleration

• Rotational speed

• Synchronization

• Phase

• Stop position

5.2 Force- and Energy-Related Control Targets

• Force

• Torque

• Pressure

• Tension

• Flow rate

• Vacuum

• Current

• Output

• Energy-supply condition

5.3 Thermal and Process-Related Control Targets

• Temperature

• Heating time

• Cooling time

• Holding time

• Product weight

• Feed quantity

• Level

• Viscosity

• Process time

5.4 State-Related Control Targets

• Product presence

• Tool condition

• Door condition

• Clamp condition

• Lubrication condition

• Supply condition

• Communication condition

• Fault condition

A control target should not be selected merely because it can be measured. It should have a meaningful influence on machine function, quality, or safety.

6. Control Variables and State Variables

Control Basis should distinguish control variables from state variables.

6.1 Control Variable

A control variable has a target value, and the system directly regulates the actual value so that it follows the target.

Examples:

• Target position

• Target speed

• Target torque

• Target temperature

• Target pressure

• Target tension

A control variable generally requires:

• Target value

• Allowable tolerance

• Measurement method

• Actuation method

• Control cycle

• Abnormal range

6.2 State Variable

A state variable is observed to determine whether the machine is currently operating normally.

Examples:

• Product arrival

• Cylinder forward completion

• Door closed

• Pneumatic supply normal

• Lubrication normal

• Communication normal

• Motor overload

A state variable is not necessarily regulated continuously, but it serves as an important criterion for operation permission and state transition.

7. Control Scope and System Boundary

The scope of responsibility of the control system must be clearly defined.

7.1 Internal Machine Boundary

• Sensors

• Actuators

• Drives

• Valves

• Motors

• Heaters

• Brakes

• Local I/O

• PLC

• HMI

7.2 External System Boundary

• Upstream and downstream equipment

• Robots

• Conveyors

• Quality-inspection equipment

• Production-management systems

• MES

• SCADA

• Remote service systems

• Customer facilities

7.3 Items to Define at the Boundary

• Signal sender and receiver

• Meaning of the signal

• Normal state

• Abnormal state

• Response time

• Default behavior during communication failure

• Reconnection condition

• Scope of responsibility

• Interface test method

If the control boundary is unclear, it becomes difficult to determine the cause and responsibility when an abnormal condition occurs between machines.

8. Control Architecture

Control architecture defines how control functions are distributed across levels and devices.

8.1 Fundamental Levels

Field Level

This level detects actual conditions and performs physical actions.

• Sensors

• Switches

• Encoders

• Motors

• Cylinders

• Valves

• Heaters

• Brakes

Device Control Level

This level controls individual devices.

• Servo drives

• Inverters

• Stepper drives

• Temperature controllers

• Valve manifolds

• Local controllers

Machine Control Level

This level controls the overall machine functions and sequences.

• PLC

• Motion controller

• Industrial PC

Safety Control Level

This level processes safety-related inputs and restricts hazardous outputs.

• Safety relay

• Safety PLC

• Safety drive functions

Operator Level

This level provides the interface between the operator and the machine.

• HMI

• Operator panel

• Push buttons

• Indicator lamps

• Warning devices

Supervisory Level

This level manages production, quality, history, and maintenance information.

• SCADA

• MES

• Data logging

• Remote monitoring

8.2 Centralized and Distributed Control

Centralized Control

A single main controller handles most control functions.

Advantages:

• Simple structure

• Easy program management

• Easy understanding of the overall sequence

Limitations:

• Wiring may become long

• Controller failure has a broad impact

• Scalability may be limited in large systems

Distributed Control

Multiple local controllers share the control functions.

Advantages:

• Easier modularization

• Reduced wiring

• Higher scalability and maintainability

Limitations:

• Higher dependence on communication

• State synchronization is required

• System integration may become more complex

The architecture should be selected according to machine size, modularity, response requirements, wiring distance, and maintenance strategy.

9. Functional Units and Control Units

The machine function should be decomposed into controllable units.

Examples:

• Feeding module

• Alignment module

• Clamping module

• Processing module

• Inspection module

• Discharge module

The following items should be defined for each control unit:

Clear definition of functional units allows control programming, assembly inspection, commissioning, and maintenance to share the same criteria.

10. Operating States and State Transitions

A machine is not defined simply by ON and OFF states.

10.1 Typical Operating States

• Power Off

• Initialization

• Ready

• Automatic

• Manual

• Setup

• Homing

• Paused

• Normal Stop

• Fault Stop

• Emergency Stop

• Recovery

• Maintenance

10.2 Definition of State Transitions

Clear conditions are required for transitions between states.

Examples:

• Initialization → Ready
  When homing and basic diagnostics are complete

• Ready → Automatic
  When automatic-operation conditions and safety conditions are satisfied

• Automatic → Fault Stop
  When an operation timeout or device fault occurs

• Fault Stop → Recovery
  When the operator confirms the abnormal condition and performs a reset

• Recovery → Ready
  When the machine position and device states have been verified

State transitions form the core structure of the control program and must be connected with operating modes, fault handling, and safety logic.

11. Fundamental Principles of Operating Modes

11.1 Automatic Operation

The machine repeatedly executes the defined process and sequence.

Required conditions:

• Homing confirmed

• Safety conditions satisfied

• Product and tool conditions confirmed

• Upstream and downstream equipment ready

• Major alarms cleared

11.2 Manual Operation

The operator directly operates individual functions or axes.

Items to review:

• To what extent should automatic interlocks remain active?

• Should limited speed be applied?

• Should movement continue only while the button is held?

• Should operation be prohibited in hazardous positions?

11.3 Setup Operation

Sensor position, speed, stroke, timing, and process conditions are adjusted.

Adjustment values should be restricted by authority level and allowable range.

11.4 Homing

The control-system position is aligned with the actual machine position.

During homing, the following should be reviewed:

• Travel direction

• Travel speed

• Sensor malfunction

• Collision possibility

11.5 Maintenance and Cleaning Mode

Limited motion may be required while guards are open or some components are removed.

The following should be defined:

• Permitted operations

• Limited speed

• Hold-to-run operation

• Interlocks that may be bypassed

• Safety functions that must remain active

12. Open-Loop and Closed-Loop Control

12.1 Open-Loop Control

The command is executed without continuously comparing and correcting the actual result.

Examples:

• Simple pneumatic cylinder

• Motor operation for a defined period

• Pulse-based stepper-motor control

• Fixed-output heater

Suitable conditions:

• Load variation is small

• High precision is not required

• The result is determined by a mechanical stop

• A separate completion-detection method is provided

12.2 Closed-Loop Control

The target value and actual value are compared, and output is adjusted to reduce the error.

Examples:

• Servo position control

• Motor speed control

• Temperature control

• Pressure control

• Pressing-force control

• Tension control

The application of closed-loop control should be determined by considering not only precision, but also disturbance, load variation, friction variation, and process quality.

13. Fundamental Principles of Interlocks

An interlock prevents operation when a specific condition is not satisfied.

13.1 Types of Interlocks

Functional Interlock

Prevents an incorrect sequence between functions.

Example:

• Machining prohibited before clamping is complete

Process Interlock

Blocks operation when product or process conditions are not satisfied.

Example:

• Pressing prohibited when no product is detected

Equipment-Protection Interlock

Prevents equipment damage.

Example:

• Spindle stopped when lubrication pressure is insufficient

Safety Interlock

Prevents risk to the operator.

Example:

• Hazardous axis stopped when a safety door is open

13.2 Items to Define for an Interlock

• Protected target

• Input condition

• Permitted operation

• Prohibited operation

• Release condition

• Whether bypass is permitted

• Bypass authority

• Restrictions during bypass

More interlocks do not necessarily mean better control. Only the necessary conditions should be configured while considering recoverability and operability.

14. Faults and Response Levels

The same stopping method should not be applied to every abnormal condition.

14.1 Normal

The machine operates within the specified range.

14.2 Automatic Correction

A small deviation is corrected automatically.

14.3 Caution

Operation may continue, but inspection is required.

14.4 Restricted Operation

The machine operates with limited speed, output, or function.

14.5 Automatic Retry

The operation is retried a limited number of times under safe conditions.

14.6 Normal Stop

The current cycle or process is safely completed before stopping.

14.7 Fault Stop

The operation is interrupted and operator action is required.

14.8 Safety Stop

The machine stops according to a defined safety procedure to limit hazardous motion and energy.

14.9 Emergency Stop

Hazardous motion is stopped as quickly as reasonably possible to reduce immediate danger.

15. Fundamental Principles of Recovery and Restart

Automatic operation should not resume immediately simply because an alarm has been cleared.

The following should be verified before recovery:

• Has the actual cause of the fault been removed?

• Can the product position be confirmed?

• Can the tool position be confirmed?

• Can the current axis position be trusted?

• Is homing required?

• Must residual products be removed?

• Are the safety devices in their normal state?

• Has the operator intentionally performed a reset?

• Are the upstream and downstream machines ready?

Restart should occur only after confirming that the machine has returned to a known state, rather than simply repeating the previous command.

16. Boundary between Mechanical Design and Control Design

The responsibilities of mechanical design and control design should be clearly distinguished.

Items That Should Be Solved Mechanically

• Structural stiffness

• Load support

• Basic positioning accuracy

• Guide alignment

• Backlash minimization

• Mechanical stops

• Drop-prevention structure

• Mechanical overload protection

Items That Should Be Solved through Control

• Position command

• Speed command

• State verification

• Sequence control

• Target-value correction

• Interlocks

• Fault detection

• Stop and recovery logic

Items That Require Joint Review

• Repeatability

• Positioning

• Vibration

• Collision prevention

• Overload

• Braking

• Home and limit positions

• Safety stopping

Control is not a means of compensating for poor mechanical design. The roles of mechanical performance and control performance must be clearly separated.

17. Interface with Assembly

The results of control design must be physically implementable during assembly.

17.1 Sensor Installation Information

• Mounting reference surface

• Installation position

• Sensing distance

• Sensing direction

• Adjustment range

• Repeatability

• Cable direction

• Contamination protection

• Replacement accessibility

17.2 Actuator Installation Information

• Alignment reference

• Coupling misalignment

• Motor mounting stiffness

• Cylinder side load

• Brake orientation

• Home position

• Mechanical limit

• Cable bending radius

17.3 Adjustment Information

• Sensor position

• Stopper position

• Belt tension

• Cylinder speed

• Pressure setting

• Servo home position

• Torque limit

• Brake clearance

Control Basis should provide standards so that control components are not installed arbitrarily based only on the assembler’s experience.

18. Interface with Manufacturing

The control system must be reproduced consistently in every manufactured machine.

18.1 Manufacturing Tolerance and Control Performance

The following should be distinguished:

• Accuracy that must be guaranteed through machining

• Range that can be corrected through assembly adjustment

• Range that can be compensated through control parameters

• Range that must be continuously corrected through feedback

18.2 Parameter Standardization

• Speed

• Acceleration

• Deceleration

• Torque limit

• Temperature

• Pressure

• Timeout

• Retry count

• Alarm criteria

• Sensor delay time

Parameters should not exist only as internal program values. They should be traceable management items for manufacturing, quality, and service.

18.3 Manufacturing Inspection

• I/O inspection

• Wiring inspection

• Rotation-direction inspection

• Individual-operation inspection

• Homing inspection

• Interlock inspection

• Automatic-operation inspection

• Alarm inspection

• Recovery inspection

• Safety-function inspection

19. Major Deliverables of Control Basis

20. Control Basis Review Questions

Purpose and Scope

• Is the purpose of control clearly defined?

• Are the control targets and system boundaries defined?

• Has the machine function been divided into controllable units?

States and Variables

• Are control variables and state variables distinguished?

• Can the actual result be verified?

• Does the sensor position represent the final state?

Architecture

• Are functions assigned to the appropriate control level?

• Is the boundary between standard control and safety control clear?

• Is the default behavior during communication failure defined?

Operation

• Are automatic, manual, setup, and recovery modes defined?

• Are state-transition conditions clear?

• Are homing and restart conditions defined?

Fault and Recovery

• Are timeout conditions defined?

• Is the range of automatic retry appropriate?

• Are conditions requiring operator intervention clear?

• Can the machine state be trusted after recovery?

Assembly and Manufacturing

• Are sensor and actuator installation criteria available?

• Can all control functions be inspected after assembly?

• Can parameters be reproduced consistently?

• Are final test and acceptance criteria defined?

21. Conclusion

Control Basis is the common design standard for implementing control in general machinery.

Its purpose is not merely to select control devices or write programs. It is to systematically define what the machine must execute, which states must be verified, under what conditions operation should be permitted, and how the machine should stop and recover when an abnormal condition occurs.

A clear Control Basis enables the following documents to be developed consistently:

• Function and State Control

• Motion and Process Control

• Sensing and State Detection

• Feedback and Regulation Control

• Interlock and Permissive Control

• Fault, Alarm, Diagnostics, and Recovery

• Safety-Related Control

• Control Hardware and System Implementation

• Manufacturing, Commissioning, and Validation

A well-defined Control Basis connects machine function, structure, and motion to an actual operable system and allows the same performance to be repeatedly implemented and verified during Assembly and Manufacturing.