1. Overview

In mechanical design, a motion / positioning module is a function module that determines in which direction, along which path, to which position, and with what stopping condition a part, target object, tool, or working section moves inside a machine.

If the drive module generates the force and power required for motion, and the power transmission module transfers or converts that power, the motion / positioning module defines how that motion actually appears as a trajectory and position.

In other words, the motion / positioning module is not simply a device that “makes something move.” It is a design area that determines the direction, path, position, repeatability, accuracy, and reference of machine motion.

For example, even if a servo motor rotates and a ball screw generates linear driving force, actual positioning accuracy cannot be secured if the linear guide layout, slider structure, stopper position, home sensor, encoder feedback, and reference surface design are not appropriate.

Therefore, the motion / positioning module should not be understood as a sub-part of the drive module or power transmission module. It should be understood as a core design module that creates accurate machine motion and work quality.

2. Definition

A motion / positioning module is a function module that determines the motion direction, motion path, stop position, repeat position, and reference position of the target object, tool, working section, or transfer section in a mechanical system.

The core purpose of a motion / positioning module can be summarized as follows:

To move the target object or working section stably to the required position and posture, and to stop repeatedly at the same position.

This module performs the following functions.

The motion / positioning module defines machine motion from the perspective of “how it moves” and “where it is positioned.”

3. Role in Mechanical Systems

A motion / positioning module performs the following roles within a mechanical system.

3.1 It Creates the Motion Path

In a machine, the generation of force alone does not create the desired motion.
The force must be guided along a defined path.

Examples include the following.

If the motion path is unstable, positioning error, vibration, jamming, wear, and product damage may occur even when the driving force is sufficient.

3.2 It Determines Positioning Accuracy and Repeatability

The motion / positioning module directly determines the positioning accuracy and repeatability of the machine.

Positioning accuracy means how accurately the system reaches the target position.
Repeatability means how consistently the system reaches the same position when the same motion is repeated.

Factors to review include:

• Accuracy of reference surfaces

• Straightness of guides

• Parallelism of rails

• Slider clearance

• Stopper position

• Sensor detection repeatability

• Homing accuracy

• Backlash

• Thermal deformation

• Frame deformation

• Deflection caused by load

When quality problems occur in a machine, the cause is often not the drive motor but clearance in the motion / positioning structure, guide alignment, or stopper repeatability.

3.3 It Determines the Relative Position Between the Target Object and the Tool

Work quality is often determined by the relative position between the target object and the tool.

Examples include the following.

Even a small change in the relative position between the tool and target object can cause cutting defects, leakage, underfilling, pressing defects, assembly defects, or inspection errors.

Therefore, the motion / positioning module is not a simple transfer device. It is a structure that creates the reference position that determines work quality.

3.4 It Creates the Machine Coordinate System and References

A machine is not a device that moves arbitrarily.
It is a system that moves around defined references.

The motion / positioning module creates the following references:

• Machine home position

• Work home position

• Product reference position

• Tool reference position

• Transfer reference line

• Height reference

• Centerline

• Stop position

• Adjustment reference

• Replacement reference

If these references are unclear, problems occur during assembly, adjustment, maintenance, and product changeover.

For example, if the reference position is not reproduced after tool replacement, readjustment is required every time.
If the reference line is unclear even after product guide adjustment, positional deviation continues during production.

3.5 It Stabilizes the Direction of Driving Force and Load

The motion / positioning module does not only determine position.
It also restricts and supports the direction of motion so that driving force and working load are transmitted stably through the structure.

Review points include:

• Load direction

• Guide layout

• Moment load

• Eccentric load

• Vertical load

• Side load

• Friction load

• Impact load

• Over-constraint

• Deformation path

If the direction of driving force and the direction of guidance do not match, slider jamming, uneven bearing wear, vibration, and positioning error may occur.

3.6 It Affects Productivity and Cycle Time

The motion / positioning module also affects machine cycle time.

If the motion path is long, acceleration and deceleration are unstable, or stabilization time after stopping is long, productivity decreases.

Review points include:

• Travel distance

• Travel speed

• Acceleration time

• Deceleration time

• Stabilization time after stopping

• Homing time

• Position confirmation time

• Clamp release and repositioning time

• Reciprocating cycle

• Product changeover adjustment time

The motion path should be as short and clear as possible, and unnecessary reciprocating motion or excessive travel distance should be reduced.

4. Main Types of Motion / Positioning Modules

Motion / positioning modules can be divided into several types according to the motion method and positioning method.

5. Types of Motion / Positioning Methods

5.1 Linear Motion Method

The linear motion method moves a target object, tool, slider, or table along a straight path.

Typical components include:

• Linear guide

• LM rail

• Slider

• Ball screw

• Lead screw

• Timing belt

• Pneumatic cylinder

• Electric actuator

• Linear motor

Advantages

• The transfer path is clear.

• Position control is relatively easy.

• It is widely used in automated equipment.

• It is easy to expand into multi-axis structures.

• It is suitable for managing the relative position between the tool and target object.

Points to Consider

• Guide alignment is important.

• Load direction and guide layout must match.

• For long strokes, deflection and vibration must be reviewed.

• Dust, cleaning water, and foreign matter ingress must be considered.

• The structure should not become over-constrained.

Design Review Points

• Travel distance

• Load direction

• Guide type

• Guide spacing

• Number of sliders

• Straightness

• Parallelism

• Repeatability

• Drive method

• Lubrication and dustproof structure

• Stopper and limit sensor

5.2 Rotary Positioning Method

The rotary positioning method rotates and stops a rotary axis, turntable, or index table at a specific angle.

Typical components include:

• Rotary table

• Index table

• Rotary shaft

• Servo motor

• Reducer

• Cam indexer

• Bearing

• Brake

• Position sensor

Advantages

• Multiple processes can be arranged in a circular layout.

• Equipment space can be reduced.

• Repeated stop positioning is possible.

• It is suitable for multi-process automation.

• Work positions can be moved sequentially.

Points to Consider

• Large rotary inertia increases acceleration and deceleration load.

• Stop position repeatability is important.

• Backlash and reducer clearance must be reviewed.

• Table deflection and rotational runout must be reviewed.

• Product separation during rotation and safety risks must be considered.

Design Review Points

• Rotation angle

• Number of divisions

• Stop position repeatability

• Rotational speed

• Acceleration and deceleration conditions

• Table inertia

• Allowable moment

• Bearing structure

• Need for brake

• Home sensor

• Safety cover

5.3 Vertical Lifting Positioning Method

The lifting method moves a target object, tool, table, or head in the vertical direction.

Typical components include:

• Ball screw lifting axis

• Linear guide

• Guide post

• Pneumatic cylinder

• Hydraulic cylinder

• Electric lifter

• Lifting table

• Counterbalance

• Brake

Advantages

• It is suitable for height adjustment and vertical work.

• It can be applied to pressing, cutting, sealing, and assembly work.

• It clearly defines the tool approach direction.

• It uses workspace efficiently.

Points to Consider

• Load in the gravity direction must be considered.

• There is a falling risk during power failure.

• Tilting caused by eccentric load must be reviewed.

• Guide stiffness is important.

• Brakes, stoppers, or fall-prevention devices may be required.

Design Review Points

• Lifting load

• Stroke

• Vertical accuracy

• Guide layout

• Eccentric load

• Fall prevention

• Brake

• Home and limit sensors

• Safety during power failure

• Maintenance accessibility

5.4 Stopper-Based Positioning Method

Stopper-based positioning determines position by bringing the target object or moving body into contact with a mechanical reference surface.

Typical components include:

• Mechanical stopper

• Locating pin

• Reference block

• End stopper

• V-block

• Centering block

• Adjustable stopper

• Damping stopper

Advantages

• The structure is simple.

• Repeated position can be secured easily.

• Dependence on sensors and control can be reduced.

• Field adjustment is relatively easy.

• Cost is low.

Points to Consider

• Impact load may occur.

• Stopper wear can create positioning error.

• Foreign matter or residue on the reference surface can change the position.

• A damping structure may be required for high-speed moving bodies.

• Product damage must be prevented.

Design Review Points

• Reference surface position

• Stopper stiffness

• Impact load

• Repeatability

• Allowable wear range

• Adjustment method

• Damping structure

• Foreign matter discharge

• Cleanability

• Replaceability

5.5 Cam and Link Motion Method

The cam and link method converts rotary motion into a specific trajectory, reciprocating motion, or timing motion.

Typical components include:

• Cam

• Follower

• Link

• Crank

• Pin joint

• Lever

• Rod end

• Guide block

Advantages

• A defined motion trajectory can be created mechanically.

• It is suitable for repeated motion.

• Constant timing can be created without electronic control.

• It can be applied to high-speed repeated equipment.

• Multiple motions can be mechanically synchronized.

Points to Consider

• Cam profile design is important.

• Wear occurs at pin joints and followers.

• Clearance affects repeatability.

• Lubrication is required.

• Adjustability may be limited.

Design Review Points

• Motion trajectory

• Cam profile

• Follower load

• Link length

• Pin load

• Clearance

• Lubrication

• Wear

• Impact

• Repeatability

• Safety cover

5.6 Sensor-Based Positioning Method

Sensor-based positioning detects and controls position using position sensors, home sensors, limit sensors, encoders, and similar elements.

Typical components include:

• Home sensor

• Limit sensor

• Proximity sensor

• Photo sensor

• Linear scale

• Rotary encoder

• Servo encoder

• Position feedback system

Advantages

• Position status can be checked by the control system.

• Automatic homing is possible.

• Abnormal positions can be detected.

• It can be combined with servo systems for precise control.

• It is easy to connect with quality data.

Points to Consider

• Sensor position repeatability is important.

• Dust, water, oil, and vibration may affect sensor performance.

• Sensors alone cannot remove mechanical clearance.

• The home sensor position and actual working position may differ.

• Wiring and noise countermeasures are required.

Design Review Points

• Sensor type

• Sensor mounting position

• Detection repeatability

• Resolution

• Response speed

• Noise resistance

• Waterproof and dustproof protection

• Homing method

• Limit position

• Interface with control system

5.7 Multi-Axis Positioning Method

The multi-axis positioning method combines two or more axes to determine position on a plane or in space.

Typical components include:

• XY table

• XYZ stage

• Gantry structure

• Cartesian robot

• Pick-and-place device

• Multi-axis servo system

• Linear motor stage

Advantages

• Complex position control is possible.

• It can respond to various product positions.

• Motion can be changed by program modification.

• It is suitable for automated processes.

• It can be applied to inspection, assembly, dispensing, cutting, and transfer.

Points to Consider

• Squareness and parallelism between axes are important.

• Error from one axis can accumulate in another axis.

• Cable and piping management must be considered.

• Control setup can become complex.

• Frame stiffness and vibration must be reviewed.

Design Review Points

• Axis configuration

• Travel range

• Squareness between axes

• Repeatability

• Interpolation control

• Cable carrier structure

• Frame stiffness

• Load and moment

• Home setting

• Safety area setting

6. Main Design Criteria

The following criteria should be reviewed when designing a motion / positioning module.

6.1 Required Motion

The first factor to review is the type of motion required.

If the required motion is unclear, it is difficult to correctly design guides, drive methods, sensors, stoppers, and reference surfaces.

6.2 Positioning Accuracy and Repeatability

One of the most important criteria in a motion / positioning module is positioning accuracy and repeatability.

Review points include:

• Target positioning accuracy

• Repeatability

• Homing accuracy

• Stop position error

• Reference surface error

• Sensor detection error

• Thermal deformation

• Load deformation

• Assembly error

• Position change after wear

Accuracy is not determined only by values in a component catalog.
Structural stiffness, load direction, assembly condition, sensor position, control conditions, and operating environment must be reviewed together.

6.3 Stiffness and Load

The motion / positioning module receives load during motion or while stopped.

Review points include:

• Moving mass

• Working load

• Eccentric load

• Moment load

• Vertical load

• Side load

• Impact load

• Acceleration load

• Frame deformation

• Guide deformation

If stiffness is insufficient, position becomes unstable, the relative position between tool and target object changes, and vibration and wear increase.

6.4 Clearance and Backlash

Clearance and backlash are major causes of positioning error in motion / positioning modules.

Review points include:

• Guide clearance

• Bearing clearance

• Ball screw backlash

• Gear backlash

• Link pin clearance

• Clamp clearance

• Stopper wear

• Loosening of fasteners

• Movement of adjustment parts

In high-precision equipment, it is important not only to reduce clearance, but also to arrange the structure so that the direction of clearance does not affect work quality.

6.5 Reference Surfaces and Adjustability

A motion / positioning module must have clear references.

Review points include:

• Reference surface position

• Reference line

• Centerline

• Height reference

• Home position

• Adjustment reference

• Scale or marking

• Stopper adjustment structure

• Position reproduction after tool replacement

• Adjustability during product changeover

Equipment without clear references is difficult to assemble and maintain, and adjustment results may vary depending on the operator.

6.6 Sensors and Feedback

Sensors are important elements that confirm the actual position and state in a positioning module.

Review points include:

• Need for home sensor

• Need for limit sensor

• Intermediate position detection

• Encoder feedback

• Need for linear scale

• Sensor mounting position

• Sensor protection

• Detection repeatability

• Control response

• Abnormal position detection

If sensors exist only at the drive section, the actual position of the working section may not be known accurately.
For precision equipment, it may be necessary to detect position near the working section.

6.7 Friction, Lubrication, and Wear

The motion / positioning module performs repeated movement, so friction and wear occur.

Review points include:

• Guide friction

• Slider friction

• Bearing friction

• Stopper wear

• Link pin wear

• Cam follower wear

• Lubrication method

• Lubrication interval

• Foreign matter ingress

• Cleaning water ingress

• Position change after wear

Wear is not simply a service-life issue.
It is a direct cause of reduced positioning accuracy and repeatability.

6.8 Safety

Because the motion / positioning module includes moving structures, safety must be reviewed.

Hazards include:

• Pinch hazard

• Entrapment hazard

• Falling vertical axis

• Collision of high-speed moving body

• Contact with rotary table

• Stopper collision

• Access during homing

• Unexpected motion during manual adjustment

• Overtravel beyond limit

• Residual motion after emergency stop

Safety design may include the following elements:

• Safety cover

• Interlock

• Mechanical stopper

• Limit sensor

• Emergency stop

• Brake

• Fall-prevention device

• Low-speed inspection mode

• Manual operation mode

• Safety area setting

7. Interface with Other Modules

The motion / positioning module is directly connected to several function modules.

7.1 Relationship with the Drive Module

The drive module generates the force and power required for motion, while the motion / positioning module determines the direction and position in which that force appears as actual motion.

Review points include:

• Does the driving force match the motion direction?

• Is the drive capacity appropriate for the moving mass and load?

• Does vibration occur during acceleration and deceleration?

• Is position control required?

• Is a brake or holding function required?

• Is the system safe during power failure?

The motion quality is not secured just because the drive module is appropriate.
Guides, stoppers, sensors, and reference surfaces must be reviewed together.

7.2 Relationship with the Power Transmission Module

The power transmission module transfers driving force to the motion / positioning module.

Review points include:

• Does backlash in belts, ball screws, gears, or links affect position?

• Does elastic deformation in the power transmission section disturb the stop position?

• Are the reduction ratio and travel speed appropriate?

• Does shaft alignment match the guide direction?

• Does over-constraint occur?

• Does wear in the transmission section affect positioning repeatability?

7.3 Relationship with the Processing / Working Module

The processing / working module requires work to be performed at the correct position for stable quality.

Work quality is created not only by processing capability, but also by accurate positioning.

7.4 Relationship with the Tooling Module

Because the tooling module is the tool section that directly contacts the target object, it strongly depends on the accuracy of the motion / positioning module.

Review points include:

• Does the tool approach the same position repeatedly?

• Is the position reproduced after tool replacement?

• Is the clearance between tool and target object constant?

• Does tool load change the position?

• Is position adjustment possible after tool wear?

• Are reference surfaces and positioning structures clear?

7.5 Relationship with the Material Handling Module

The material handling module must supply the target object to the position required by the motion / positioning module.

Review points include:

• Is the target object supplied accurately to the reference position?

• Does the feeding direction match the working position?

• Is the posture of the target object maintained during transfer?

• Does the product shake at the stopper or guide?

• Do feeding speed and positioning time match?

• Does the discharge motion conflict with the next process?

7.6 Relationship with the Control / Sensing Module

The control / sensing module confirms and corrects the positioning state.

Review points include:

• Is the homing procedure clear?

• Are limit sensors located at safe positions?

• Is working position detection possible?

• Can positioning error be detected?

• Does the sensor position match the mechanical reference?

• Is position compensation possible in the control program?

• Can the system stop safely at abnormal positions?

8. Application in Food Machinery

In food machinery, the motion / positioning module is connected not only to product quality but also to hygiene, cleanability, and contamination prevention.

Important conditions for motion / positioning modules in food machinery include the following.

In food machinery, linear guides, ball screws, bearings, and sensors are easily exposed to cleaning water and food residue.
Therefore, in addition to positioning accuracy, it is necessary to review whether repeatability is maintained after cleaning, whether lubricant contamination occurs, and whether residue remains on reference surfaces that contact the product.

9. Common Design Mistakes

Common design mistakes in motion / positioning modules include the following.

9.1 Judging Positioning Accuracy Only by the Drive Unit

Using a servo motor does not automatically secure positioning accuracy.

Actual positioning accuracy is determined by guide alignment, ball screw backlash, coupling torsion, frame stiffness, sensor position, and load deformation.

9.2 Over-Constraining the Guide and Drive Axis

If the centerlines of the guide and the ball screw, cylinder, or link do not match, motion will not be smooth and jamming may occur.

Over-constrained structures cause increased friction, wear, vibration, positioning error, and reduced component life.

9.3 Not Defining Reference Surfaces and Home Position Clearly

If reference surfaces and home position are not clear, assembly, adjustment, maintenance, and product changeover all become difficult.

In particular, if position is not reproduced after tool replacement, guide adjustment, or stopper adjustment, dependence on operator skill increases.

9.4 Deciding Stopper and Sensor Positions Too Late

Stoppers and sensors are core elements of positioning.
If they are added later, accessibility, protection structure, wiring, and maintainability can become poor.

Stoppers and sensors should be placed together during the initial structural design stage.

9.5 Ignoring Cleanability and Protection of Lubricated Areas

In food machinery, if linear guides, ball screws, and bearings are exposed to cleaning water and product residue, positioning accuracy and service life can decrease significantly.

Therefore, waterproofing, dustproofing, drainage, covers, and separation of lubricated areas must be considered during the initial design stage.

10. Design Checklist

The following questions can be used when designing a motion / positioning module.

10.1 Motion Requirement Review

• Is the required motion linear, rotary, lifting, reciprocating, or curved?

• What are the travel distance or rotation angle?

• Is intermediate stopping required?

• Is synchronization with other axes or processes required?

• What are the travel speed and cycle time?

10.2 Positioning Accuracy Review

• What is the target positioning accuracy?

• What repeatability is required?

• Is homing accuracy sufficient?

• How does positioning error affect product quality?

• Does the sensor position match the actual working position?

10.3 Structure and Stiffness Review

• Is the guide layout suitable for the load direction?

• Can the structure withstand eccentric load and moment load?

• Are frame and slider stiffness sufficient?

• Can shaft alignment and guide parallelism be secured?

• Does over-constraint occur?

10.4 Reference and Adjustment Review

• Are reference surfaces and reference lines clear?

• Are home position and working position clear?

• Can the stopper be adjusted?

• Is the position reproduced after tool replacement?

• Is adjustment easy during product changeover?

10.5 Sensor and Safety Review

• Are home sensors and limit sensors required?

• Are sensors protected from water, dust, and vibration?

• Can overtravel beyond the limit be prevented?

• Can falling of a vertical axis be prevented?

• Is a safe state maintained after emergency stop?

10.6 Maintenance and Cleaning Review

• Are guides, stoppers, and sensors accessible?

• Is lubrication and inspection possible?

• Can wear condition be checked?

• Does cleaning water drain properly?

• Are food-contact areas separated from lubricated areas?

• Is positioning repeatability maintained after cleaning?

11. Summary

A motion / positioning module is a core function module that determines in which direction and along which path the target object, tool, working section, or transfer section moves inside the machine, and at which position it stops.

This module may consist of linear guides, sliders, rotary tables, index tables, ball screws, stoppers, reference surfaces, sensors, cams, links, and multi-axis stages. It directly affects machine positioning accuracy, repeatability, motion stability, and work quality.

When designing a motion / positioning module, the designer should not stop at simply creating a moving structure.
Required motion, positioning accuracy, repeatability, stiffness, load, clearance, backlash, reference surfaces, sensors, adjustability, safety, maintainability, and cleanability must be reviewed together.

This module is also closely connected to the drive module, power transmission module, processing / working module, tooling module, material handling module, and control / sensing module.

In food machinery, cleaning accessibility, residue prevention, separation of lubricated areas, waterproofing, dustproofing, drainability, and product damage prevention must be considered together.

Therefore, the motion / positioning module should be understood not as a simple transfer device, but as a central design module that determines machine motion quality and work quality.