1. Overview

A machine performs its intended function by transmitting the force and motion generated by a power source to the working unit and converting them into the required direction, speed, trajectory, force, and operating cycle.

In this process, a mechanism refers to the mechanical structure and principle used to transmit or transform motion, while motion refers to the actual form and characteristics of movement generated by the mechanism.

Mechanism & Motion can therefore be understood through the following sequence:

Input power → Motion transmission → Motion conversion → Motion guidance and constraint → Output motion → Work execution

Mechanism and motion are not separate concepts. They are closely interconnected. A mechanism receives an input motion and generates a specific output motion, while the same type of motion can be produced by different mechanisms.

Part I. Classification of Mechanisms

2. Motion Transmission Mechanisms

A motion transmission mechanism transfers motion and power from an input shaft to another shaft or component.

Its main purpose is to maintain the basic form of motion while changing rotational speed, torque, rotational direction, or shaft position.

2.1 Gear Transmission Mechanisms

Gear transmission mechanisms transfer rotational motion and torque through the engagement of gear teeth.

Major types include:

• Spur gears

• Helical gears

• Bevel gears

• Worm and worm wheels

• Internal gears

• Planetary gears

• Rack and pinion systems

• Compound gear trains

Gear mechanisms are suitable for systems that require accurate speed ratios and synchronized rotational motion. However, backlash, noise, lubrication, and tooth surface strength must be considered.

2.2 Belt and Pulley Mechanisms

Belt and pulley mechanisms transmit rotational motion between two shafts located at a distance from each other.

Major types include:

• Flat belts

• V-belts

• Timing belts

• Poly-V belts

Belt mechanisms have a simple structure, operate relatively quietly, and are suitable for long center distances. Timing belts can transmit synchronized motion without slippage.

2.3 Chain and Sprocket Mechanisms

Chain and sprocket mechanisms are used to transmit rotational motion or linear conveying motion.

Typical applications include:

• Conveyors

• Product transfer systems

• Power transmission shafts

• Lifting devices

• Intermittent transfer systems

Chain mechanisms are suitable for high loads and long transfer distances, but lubrication, tension adjustment, noise, and wear must be properly managed.

2.4 Shaft and Coupling Mechanisms

A shaft transmits rotational motion and torque, while a coupling connects two separate shafts.

Major components include:

• Rotating shafts

• Keys and splines

• Flexible couplings

• Rigid couplings

• Universal joints

• Torque limiters

Couplings may also compensate for shaft misalignment, angular error, and axial displacement.

2.5 Friction Drive Mechanisms

Friction drive mechanisms transmit motion through friction between two components.

Typical examples include:

• Friction wheels

• Roller drives

• Clutches

• Brakes

• Friction feeders

These mechanisms are structurally simple and can protect components by slipping under overload. However, they have limitations when an exact speed ratio must be maintained.

3. Motion Conversion Mechanisms

A motion conversion mechanism changes one form of input motion into another form of output motion.

Typical motion conversions include:

• Rotary motion to linear motion

• Rotary motion to reciprocating motion

• Rotary motion to oscillating motion

• Continuous motion to intermittent motion

• Linear motion to rotary motion

3.1 Screw Mechanisms

A screw mechanism converts rotary motion into linear motion using the helical geometry of screw threads.

Major types include:

• Lead screws

• Ball screws

• Trapezoidal screws

• Square-thread screws

• Roller screws

• Differential screws

Screw mechanisms are used for precision positioning, lifting, clamping, pressing, and electric cylinders.

Ball screws offer high efficiency and precision, while trapezoidal screws have a simpler structure and may provide self-locking characteristics under certain conditions.

3.2 Rack and Pinion Mechanisms

A rack and pinion mechanism combines a circular pinion gear with a straight rack gear to convert rotary motion into linear motion, or vice versa.

It is suitable for applications requiring long travel distances and high travel speeds.

Typical applications include:

• Gantry systems

• Automatic doors

• Large linear axes

• Lifting systems

• Steering mechanisms

3.3 Crank-Slider Mechanisms

A crank-slider mechanism converts the rotary motion of a crank into the reciprocating linear motion of a slider.

Typical applications include:

• Presses

• Pumps

• Compressors

• Reciprocating cutting machines

• Packaging machines

The position and velocity of the slider change nonlinearly according to the crank angle.

3.4 Scotch Yoke Mechanisms

A Scotch yoke mechanism converts rotary motion into linear reciprocating motion as a rotating crank pin moves within a slot.

It has a simple structure and can produce a relatively uniform reciprocating motion. However, friction and wear between the pin and slot can be significant.

3.5 Eccentric Mechanisms

An eccentric mechanism generates reciprocating or oscillating motion by intentionally offsetting the center of rotation from the operating point.

Typical applications include:

• Vibrating devices

• Feeders

• Small presses

• Reciprocating cutting devices

• Screening equipment

3.6 Cam Mechanisms

A cam mechanism uses the profile of a cam to convert rotary motion into linear or oscillating motion.

A cam does more than change the direction of motion. It also determines the position, velocity, acceleration, and dwell time of the follower.

Major cam types include:

• Plate cams

• Cylindrical cams

• Barrel cams

• Face cams

• Linear cams

• Conjugate cams

Follower types include:

• Roller followers

• Flat-faced followers

• Spherical followers

• Translating followers

• Oscillating followers

Cam mechanisms are suitable for filling machines, packaging machines, labeling machines, and cutting machines that require precise motion sequences and timing.

4. Linkage Mechanisms

A linkage mechanism consists of multiple rigid links connected by revolute joints or prismatic joints to generate a specific motion or trajectory.

4.1 Four-Bar Linkages

A four-bar linkage is one of the most fundamental linkage mechanisms and consists of four links and four revolute joints.

Major types include:

• Crank-rocker mechanisms

• Double-crank mechanisms

• Double-rocker mechanisms

• Parallel linkages

• Trapezoidal linkages

Four-bar linkages are used to convert rotary motion into oscillating motion or to generate a specific trajectory.

4.2 Slider Linkages

Slider linkages combine revolute joints and prismatic joints.

Major types include:

• Crank-slider mechanisms

• Offset crank-slider mechanisms

• Double-slider mechanisms

• Toggle linkages

4.3 Parallel Linkages

A parallel linkage moves an output link while maintaining its orientation.

Typical applications include:

• Lifting tables

• Robotic grippers

• Parallel opening and closing devices

• Workpiece orientation-maintaining systems

4.4 Multi-Link Mechanisms

Multi-link mechanisms use six or more links to generate complex trajectories or motion characteristics.

Major types include:

• Six-bar linkages

• Eight-bar linkages

• Pantographs

• Robotic linkages

• Path-generating linkages

Multi-link mechanisms are useful for complex path generation and orientation control, but their design and kinematic analysis are more complicated.

5. Intermittent Motion and Indexing Mechanisms

An intermittent motion mechanism converts continuous input motion into repeated periods of movement and dwell.

5.1 Geneva Mechanisms

A Geneva mechanism uses a driving pin that enters the slots of a Geneva wheel and rotates it through a fixed angle.

It is suitable for indexing motions that require rotation by a specific angle followed by a dwell period.

5.2 Ratchet and Pawl Mechanisms

A ratchet and pawl mechanism produces stepwise motion in one direction or prevents reverse rotation.

Typical applications include:

• Manual indexing

• Winding devices

• Tension adjusters

• Anti-reverse devices

5.3 Cam Indexers

A cam indexer uses a cam profile to rotate an output shaft through a fixed angle and hold it in position.

Compared with a Geneva mechanism, it generates less motion shock and is more suitable for high-speed and high-precision operation.

5.4 Star Wheels

A star wheel separates products at regular intervals or transfers them through rotational indexing.

It is commonly used for bottles, containers, food products, and packaged goods.

5.5 Escapement Mechanisms

An escapement mechanism separates and releases products or components one at a time.

Typical applications include:

• Component feeding systems

• Vibratory feeders

• Packaging machines

• Automatic assembly machines

6. Guidance and Constraint Mechanisms

Guidance and constraint mechanisms restrict moving components so that they move only in the intended direction or along the intended path.

6.1 Linear Guidance Mechanisms

Linear guidance mechanisms maintain the direction and accuracy of linear motion.

Major types include:

• Linear motion guides

• Linear shafts and bushings

• Dovetail guides

• Cross-roller guides

• Slide rails

• Telescopic guides

6.2 Rotary Guidance Mechanisms

Rotary guidance mechanisms support shafts or rotating components so that they rotate about a defined center.

Major types include:

• Rolling-element bearings

• Plain bearings

• Bushings

• Hinges

• Pivots

• Turntable bearings

6.3 Path Guidance Mechanisms

Path guidance mechanisms guide a moving component along a defined curve or slot.

Major types include:

• Slot-and-pin mechanisms

• Cam tracks

• Curved rails

• Roller tracks

• Link-guided systems

A guidance mechanism generally does not generate motion directly. Instead, it restricts the degrees of freedom so that only the intended motion is possible.

7. Force Amplification and Clamping Mechanisms

A force amplification mechanism converts a small input force into a larger output force.

7.1 Lever Mechanisms

A lever amplifies force or displacement by using the difference in distance between the pivot and the points of applied force.

Increasing the lever length increases the output force but reduces the output displacement.

7.2 Toggle Mechanisms

A toggle mechanism generates a very large output force when two links approach a straight-line position.

Typical applications include:

• Presses

• Mold clamping

• Door locking

• Jigs and fixtures

• Injection molding machines

7.3 Wedge Mechanisms

A wedge mechanism changes the direction of input motion and amplifies force using an inclined surface.

It is used for clamping, positioning, height adjustment, and clearance compensation.

7.4 Eccentric and Cam Clamps

Eccentric and cam clamps use the rotation of an eccentric shaft or cam to secure a component with a short operating stroke.

They are fast to operate and suitable for repetitive work.

7.5 Screw Clamps

A screw clamp uses the high mechanical advantage of a screw mechanism to generate a large clamping force.

Its structure is simple and its holding force is stable, although its operating speed is relatively slow.

8. Locking, Stopping, and Safety Mechanisms

Locking and stopping mechanisms maintain a moving component in a specific position or prevent it from moving beyond an allowable range.

Major types include:

• Latches

• Detents

• Locking pins

• Spring plungers

• Over-center locks

• Brakes

• Stoppers

• Anti-reverse mechanisms

• Torque limiters

• Slip clutches

These mechanisms provide not only positional holding, but also protection for equipment and operators against overload, collision, and unexpected reverse motion.

9. Elastic and Return Mechanisms

Elastic mechanisms store and release elastic energy to generate return force, tension, cushioning force, or contact force.

Major types include:

• Compression springs

• Extension springs

• Torsion springs

• Leaf springs

• Constant-force springs

• Gas springs

• Rubber elastomers

• Counterbalances

Their main functions include:

• Returning a moving part to its original position

• Maintaining tension

• Absorbing impact

• Compensating for load

• Maintaining contact force

• Correcting positional error

• Isolating vibration

10. Compliant Mechanisms

A compliant mechanism generates motion through elastic deformation of the material instead of conventional pin joints or bearing joints.

Major types include:

• Flexure hinges

• Compliant links

• Leaf-spring guides

• Compliant grippers

• Precision positioning mechanisms

• Monolithic compliant mechanisms

Advantages of compliant mechanisms include:

• Almost no backlash

• Low friction and wear

• No lubrication requirement

• Reduced number of components

• Suitability for micro-motion

However, their range of motion is limited, and repeated stress and fatigue life must be carefully evaluated.

Part II. Classification of Motion

11. Classification by Motion Path

11.1 Linear Motion

Linear motion is movement along a straight path.

Major forms include:

• Horizontal linear motion

• Vertical linear motion

• Inclined linear motion

• Single-axis linear motion

• Multi-axis linear motion

Linear motion can be generated by cylinders, ball screws, rack and pinion systems, belt-driven axes, and linear motors.

11.2 Rotary Motion

Rotary motion is movement around a fixed axis.

Major forms include:

• Continuous rotation

• Limited-angle rotation

• Forward rotation

• Forward and reverse rotation

• Multi-turn rotation

• Partial rotation

11.3 Reciprocating Motion

Reciprocating motion repeatedly moves forward and backward along the same path.

Major forms include:

• Linear reciprocating motion

• Vertical reciprocating motion

• Horizontal reciprocating motion

• Symmetrical reciprocating motion

• Asymmetrical reciprocating motion

• Variable-stroke reciprocating motion

11.4 Oscillating Motion

Oscillating motion is repeated angular movement within a limited range about a fixed pivot.

Major forms include:

• Fixed-angle oscillation

• Variable-angle oscillation

• Symmetrical oscillation

• Asymmetrical oscillation

• Damped oscillation

11.5 Helical Motion

Helical motion combines rotary motion and linear motion simultaneously.

Typical applications include:

• Screw feeding

• Extrusion screws

• Screw conveyors

• Drill feeding

• Bottle cap tightening

11.6 Curvilinear Motion

Curvilinear motion follows a curved path rather than a straight line or simple circular arc.

Major forms include:

• Circular-arc motion

• Elliptical motion

• Cycloidal motion

• Free-form curved motion

• Cam-profile motion

11.7 Compound Motion

Compound motion combines two or more motions either simultaneously or sequentially.

Typical examples include:

• Combined rotary and linear motion

• Combined linear and oscillating motion

• Multi-axis interpolated motion

• Robot end-effector motion

• Spatial curved-path motion

12. Classification by Time Characteristics

12.1 Continuous Motion

Continuous motion proceeds without stopping.

Typical examples include:

• Conveyors

• Rotating shafts

• Pumps

• Blowers

• Continuous extruders

12.2 Intermittent Motion

Intermittent motion repeatedly alternates between movement and dwell.

Typical examples include:

• Index tables

• Pitch feeding systems

• Product separation systems

• Packaging machines

• Automatic assembly machines

12.3 Cyclic Motion

Cyclic motion repeats the same or a similar movement at regular intervals.

Typical examples include:

• Reciprocating motion

• Oscillating motion

• Repetitive pressing

• Pump piston motion

• Cam-driven motion

12.4 Non-Cyclic Motion

Non-cyclic motion changes according to operating conditions or control commands without a fixed repeating cycle.

Typical examples include:

• Robot paths

• Servo positioning

• Automated storage and retrieval systems

• Programmed multi-axis motion

13. Classification by Speed and Position Characteristics

13.1 Constant-Speed Motion

Constant-speed motion maintains a fixed operating speed.

It is commonly used in conveyors, agitators, and constant-speed rotating shafts.

13.2 Acceleration and Deceleration Motion

Acceleration and deceleration motion involves changes in speed during starting and stopping.

An appropriate acceleration and deceleration profile is required to reduce mechanical shock and vibration.

13.3 Positioning Motion

Positioning motion moves a component to a target position and stops it there.

Typical applications include:

• Servo axes

• Stepper motor axes

• Index tables

• Robots

• Automatic assembly machines

13.4 Synchronized Motion

Synchronized motion occurs when two or more axes or devices maintain a defined speed ratio or phase relationship.

Typical applications include:

• Electronic cam systems

• Packaging machines

• Printing equipment

• Multi-axis transfer systems

• Synchronized cutting systems

13.5 Following Motion

Following motion occurs when one axis follows the position, velocity, or trajectory of a reference axis.

Master-slave control and electronic gearing are representative methods.

14. Classification by Actuation Method

14.1 Manual Motion

Manual motion is generated directly by human force.

Examples include:

• Handwheels

• Levers

• Pedals

• Manual slides

• Hand cranks

14.2 Mechanically Generated Automatic Motion

This type of motion is generated automatically by mechanical elements such as cams, linkages, gears, and springs.

14.3 Pneumatically Actuated Motion

Pneumatically actuated motion uses compressed air to generate linear or rotary movement.

Typical actuators include:

• Pneumatic cylinders

• Rodless cylinders

• Pneumatic grippers

• Rotary actuators

Pneumatic systems have a simple structure and are suitable for high-speed operation, but they have limitations in precise position and speed control.

14.4 Hydraulically Actuated Motion

Hydraulically actuated motion uses hydraulic pressure to generate large forces and torques.

Typical actuators and systems include:

• Hydraulic cylinders

• Hydraulic motors

• Hydraulic presses

• Hydraulic clamps

Hydraulic systems are suitable for heavy loads, but leakage, contamination, heat generation, and maintenance must be considered.

14.5 Electrically Actuated Motion

Electrically actuated motion uses electric motors to generate and control motion.

Major drive sources include:

• Induction motors

• Brake motors

• Stepper motors

• Servo motors

• Linear motors

• Electric cylinders

Electric drive systems are highly suitable for position, speed, torque, and synchronization control.

Part III. Relationship Between Mechanism and Motion

15. Functional Connection Between Mechanism and Motion

Mechanism and motion can be understood through the following five stages.

15.1 Input Motion

Input motion is the initial motion generated by a power source.

Examples include:

• Rotary motion of a motor

• Linear motion of a cylinder

• Manual motion generated by an operator

15.2 Motion Transmission

Motion is transmitted to the required location.

Examples include:

• Gears

• Belts

• Chains

• Shafts

• Couplings

15.3 Motion Conversion

The input motion is converted into the motion required by the working unit.

Examples include:

• Ball screws

• Rack and pinion systems

• Crank-slider mechanisms

• Cams

• Linkages

15.4 Motion Guidance and Constraint

The moving component is restricted so that it moves in the intended direction or along the intended path.

Examples include:

• Linear motion guides

• Bearings

• Slots

• Curved rails

• Link joints

15.5 Output Motion

Output motion is the final motion generated at the working unit.

Examples include:

• Vertical movement of a nozzle

• Reciprocating movement of a cutting blade

• Opening and closing of a clamp

• Conveyor transport

• Indexing of a rotary table

For example, a filling nozzle lifting system driven by a servo motor can be analyzed as follows:

Rotary motion of the servo motor
→ Power transmission through a coupling
→ Rotary-to-linear conversion by a ball screw
→ Linear constraint by a linear motion guide
→ Vertical positioning motion of the nozzle

Part IV. Design and Selection Criteria

16. Functional Requirements

Before selecting a mechanism, the required output motion must first be defined.

The following items should be identified:

• Direction of motion

• Travel distance or rotation angle

• Maximum speed

• Acceleration and deceleration

• Operating cycle

• Dwell time

• Positioning accuracy

• Repeatability

• Required force and torque

• Operating frequency

17. Load Conditions

The magnitude and direction of loads acting on the mechanism must be evaluated.

Major load conditions include:

• Static loads

• Repeated loads

• Impact loads

• Inertial loads

• Eccentric loads

• Axial loads

• Radial loads

• Moment loads

The design should not be limited to motor capacity calculations. Stress, deformation, wear, and fatigue of the entire mechanism must also be evaluated.

18. Motion Performance

The performance of a mechanism can be evaluated using the following criteria:

• Positioning accuracy

• Repeatability

• Backlash

• Stiffness

• Vibration

• Noise

• Friction

• Efficiency

• Response speed

• Smoothness of motion

In high-speed machinery, acceleration and jerk are particularly important. Abrupt changes in motion can increase shock, vibration, product damage, and component fatigue.

19. Environmental Conditions

Materials and structures must be selected according to the operating environment.

Major environmental conditions include:

• Temperature

• Humidity

• Dust

• Moisture

• Washdown water

• Corrosive substances

• Food contact

• Vacuum

• Cleanroom conditions

• Explosion hazards

In food machinery, hygienic design, cleanability, lubricant leakage, crevices, and the possibility of contamination accumulation must also be considered.

20. Maintainability

A mechanism should be designed not only for normal operation but also for easy inspection, adjustment, lubrication, and replacement.

Major considerations include:

• Lubrication access

• Tension adjustment

• Backlash adjustment

• Space for component replacement

• Ease of disassembly and assembly

• Service life of consumable parts

• Use of standard components

• Inspection accessibility

• Fault diagnosis capability

Part V. Recommended Classification Structure

21. Mechanism Classification

Mechanisms can be classified as follows.

A. Motion Transmission

• Gear Drive

• Belt and Pulley

• Chain and Sprocket

• Shaft and Coupling

• Friction Drive

B. Motion Conversion

• Screw Mechanism

• Rack and Pinion

• Crank-Slider

• Scotch Yoke

• Cam Mechanism

• Eccentric Mechanism

C. Linkage and Path Generation

• Four-Bar Linkage

• Slider Linkage

• Parallel Linkage

• Multi-Link Mechanism

• Trajectory Mechanism

D. Guidance and Constraint

• Linear Guide

• Rotary Guide

• Bearing and Pivot

• Slot and Track

• Curved Guide

E. Intermittent and Indexing

• Geneva Mechanism

• Ratchet Mechanism

• Cam Indexer

• Star Wheel

• Escapement

F. Force, Clamping, and Holding

• Lever

• Toggle Mechanism

• Wedge

• Clamp

• Locking Mechanism

• Brake and Stopper

G. Elastic and Compliant Mechanisms

• Spring Mechanism

• Counterbalance

• Flexure Hinge

• Elastic Link

• Compliant Mechanism

22. Motion Classification

Motion can be classified as follows.

A. Motion Path

• Linear Motion

• Rotary Motion

• Reciprocating Motion

• Oscillating Motion

• Helical Motion

• Curvilinear Motion

• Compound Motion

B. Motion Timing

• Continuous Motion

• Intermittent Motion

• Cyclic Motion

• Non-Cyclic Motion

C. Motion Control

• Constant-Speed Motion

• Variable-Speed Motion

• Positioning Motion

• Synchronized Motion

• Following Motion

D. Motion Actuation

• Manual Motion

• Mechanical Motion

• Pneumatic Motion

• Hydraulic Motion

• Electric Motion

23. Conclusion

A mechanism is not merely a collection of mechanical elements. It represents the mechanical logic and structure used to convert input motion and power into the desired output motion.

Likewise, motion does not refer only to basic forms such as linear, rotary, or reciprocating movement. It also includes speed, acceleration, cycle time, dwell time, synchronization, and positioning accuracy.

Therefore, the following design sequence is recommended when analyzing or designing a mechanism and motion system:

Define the required function
→ Define the output motion
→ Analyze load and speed conditions
→ Select the motion conversion principle
→ Select the transmission and guidance mechanisms
→ Determine the actuator and control method
→ Review safety, durability, and maintainability

This classification structure goes beyond simply organizing mechanical elements by type. It provides a systematic framework that enables designers to compare and select mechanisms and motion methods according to functional requirements.