1. Overview
An intermittent mechanism is a mechanical system that converts continuous rotary or reciprocating input motion into repeated movement and dwell at defined intervals.
An indexing mechanism is a type of intermittent mechanism that moves an output shaft or working table to a predetermined position or angle and holds it stationary for a specified period.
The basic operating sequence is:
Continuous input motion
→ Acceleration
→ Movement through a specified angle or distance
→ Deceleration
→ Dwell and position holding
→ Repetition of the next cycle
Typical applications include:
Positioning a rotary table at individual process stations
Feeding packaging material by a fixed length
Distributing containers to filling positions
Supplying components one at a time
Moving products between assembly stations
Intermittent film feeding
Separating products at a constant pitch
Providing dwell time for cutting and sealing operations
The performance of an intermittent mechanism is not determined solely by its ability to move through a specified angle. The following factors must also be considered:
Index angle
Index time
Dwell time
Acceleration
Jerk
Output-shaft inertia
Positioning repeatability
Dwell rigidity
Backlash
Shock and vibration
Overload protection
Service life and maintainability
2. Difference Between Intermittent and Indexing Mechanisms
2.1 Intermittent Mechanisms
An intermittent mechanism is a general mechanism that converts continuous motion into repeated movement and dwell.
Possible output motions include:
Intermittent rotation
Intermittent linear motion
Step feeding
One-direction ratcheting motion
Periodic opening and closing
Single-product separation
Periodic release motion
Typical examples include:
Geneva mechanisms
Ratchet-and-pawl mechanisms
Intermittent gears
Escapement mechanisms
Star wheels
Cam-driven stoppers
2.2 Indexing Mechanisms
An indexing mechanism moves an output shaft or table precisely to a target position and holds that position during the dwell period.
Typical examples include:
Cam indexers
Geneva indexers
Servo indexing tables
Ratchet indexing devices
Precision rotary tables
Linear indexing conveyors
2.3 Main Difference
Intermittent mechanisms primarily focus on the repeated sequence of movement and dwell.
Indexing mechanisms additionally emphasize positioning performance such as:
Target-position accuracy
Positioning repeatability
Rigidity during dwell
Resistance to external disturbance
Acceleration and deceleration characteristics
Synchronization between processes
Therefore, all indexing mechanisms perform intermittent motion, but not all intermittent mechanisms are precision indexing mechanisms.
3. Main Functions of Intermittent and Indexing Mechanisms
3.1 Division of Continuous Motion
Continuous motor rotation is divided into a number of independent motion segments.
Example:
Continuous motor rotation
→ 60° rotation
→ Dwell
→ Another 60° rotation
→ Dwell
3.2 Constant-Pitch Feeding
Products, film, chains, or conveyors are moved by a fixed distance.
3.3 Provision of Dwell Time
The workpiece is held stationary for filling, cutting, sealing, inspection, or assembly.
3.4 Distribution to Process Positions
Multiple process stations are arranged around one rotary table, and products are transferred sequentially between them.
3.5 Product Separation
Continuously supplied products are separated individually or in defined quantities.
3.6 Process Synchronization
The phase relationship between feeding, cutting, sealing, discharge, and other operations is synchronized mechanically or electronically.
3.7 Position Holding and Locking
The output section is mechanically locked or restrained during dwell so that it does not move under external or inertial loads.
3.8 Prevention of Reverse Rotation
Ratchets, one-way clutches, or locking devices are used to prevent reverse rotation of the output shaft.
4. Basic Operating Cycle
One cycle of an indexing mechanism generally consists of the following stages.
4.1 Acceleration Stage
The output starts from rest and accelerates toward its maximum velocity.
4.2 Motion Stage
The output moves toward the target position.
Depending on the selected motion profile, the velocity may continue to vary throughout this stage.
4.3 Deceleration Stage
The output velocity decreases before reaching the target position.
4.4 Dwell Stage
The output remains stationary at the target position while the process operation is performed.
4.5 Locking Stage
When required, the output is mechanically restrained or held by a brake during dwell.
5. Main Time and Angle Variables
5.1 Cycle Time
The total time required to complete one movement and dwell cycle is called cycle time.
t_cycle = t_index + t_dwell
Where:
t_cycle: Total cycle time
t_index: Indexing time
t_dwell: Dwell time
5.2 Cycle Frequency
The number of indexing cycles per minute can be expressed as:
Cycles per minute = 60 / t_cycle
Here, t_cycle is expressed in seconds.
5.3 Index Angle
If the output table is divided into N equal stations, the index angle per movement is:
θ_index = 360° / N
For example, the index angle of an eight-station table is:
θ_index = 360° / 8 = 45°
5.4 Dwell Ratio
The proportion of the total cycle occupied by the dwell period is:
Dwell ratio = t_dwell / t_cycle
5.5 Index Ratio
The proportion of the total cycle occupied by the indexing movement is:
Index ratio = t_index / t_cycle
Therefore:
Dwell ratio + Index ratio = 1
6. Basic Classification of Intermittent and Indexing Mechanisms
6.1 Mechanical Intermittent Mechanisms
Geneva mechanisms
Ratchet and pawl
Intermittent gears
Incomplete gears
Star wheels
Escapement mechanisms
Cam-driven stoppers
One-way-clutch feeding mechanisms
6.2 Mechanical Precision Indexing Mechanisms
Barrel cam indexers
Globoidal cam indexers
Flat cam indexers
Parallel cam indexers
Roller gear cam indexers
Turret cam indexers
6.3 Electric and Servo Indexing Mechanisms
Direct servo-motor drive
Servo motor with gear reducer
Servo rotary tables
Direct-drive torque motors
Stepper-motor indexing
Linear-motor indexing
6.4 Fluid-Power Intermittent Mechanisms
Pneumatic cylinder with ratchet
Hydraulic indexing cylinder
Rotary actuator with locking pin
Cylinder-driven escapement
6.5 Classification by Output Form
Intermittent rotary type
Intermittent linear type
Step-feed type
Rotary-table type
Linear-transfer type
Product-separation type
One-direction accumulation type
7. Geneva Mechanisms
7.1 Definition
A Geneva mechanism is a representative mechanical indexing mechanism that converts continuous input rotation into intermittent output rotation through a fixed angle.
A pin on the driving wheel enters a slot in the Geneva wheel and rotates the output wheel. When the pin leaves the slot, the output wheel remains stationary.
7.2 Main Components
Driving wheel
Driving pin
Geneva wheel
Radial slots
Locking disc
Locking surface
Input shaft
Output shaft
Support bearings
7.3 Operating Principle
One cycle of a Geneva mechanism proceeds as follows:
Driving pin approaches the slot
→ Pin enters the slot
→ Geneva wheel rotates
→ Pin leaves the slot
→ Locking disc restrains the output wheel
→ Dwell is maintained
7.4 Index Angle
If the number of slots is N, the index angle per cycle is:
θ_index = 360° / N
As the number of slots increases, the index angle per movement decreases.
7.5 Main Types
External Geneva Mechanism
The driving wheel and Geneva wheel engage externally. This is the most common arrangement.
Internal Geneva Mechanism
The driving pin drives slots formed in an internal Geneva wheel.
It may provide smoother motion characteristics than the external type under certain conditions.
Spherical Geneva Mechanism
Intermittent rotation is transmitted between intersecting shafts in a spatial arrangement.
Linear Geneva Mechanism
Rotary input is converted into intermittent linear movement.
7.6 Advantages
Relatively simple structure
Movement and dwell without complex control
Index angle determined mechanically
Mechanical locking possible during dwell
Relatively low manufacturing cost
Easy application in low- and medium-speed systems
7.7 Disadvantages
Impact occurs as the pin enters and leaves the slot
Vibration and noise increase at high speed
High contact stress occurs between pin and slot
Output acceleration and jerk characteristics are limited
Index angle and dwell ratio are difficult to change
Backlash and slot wear affect positioning accuracy
7.8 Typical Applications
Small indexing tables
Film feeding systems
Packaging machines
Automatic assembly machines
Product distribution devices
Inspection-position switching systems
Low-speed rotary feeders
8. Ratchet-and-Pawl Mechanisms
8.1 Definition
A ratchet-and-pawl mechanism converts reciprocating or limited-angle rotary input into stepwise rotation in one direction.
The ratchet teeth and pawl engage to prevent reverse rotation.
8.2 Main Components
Ratchet wheel
Driving pawl
Holding pawl
Driving lever
Return spring
Shaft
Stopper
8.3 Operating Principle
Driving lever advances
→ Driving pawl rotates the ratchet wheel by one pitch
→ Holding pawl maintains the position
→ Driving lever returns
→ Driving pawl moves to the next tooth
8.4 Main Types
External ratchet
Internal ratchet
Single-pawl type
Dual-pawl type
Bidirectional selectable ratchet
Manual lever ratchet
Pneumatically driven ratchet
Roller ratchet
8.5 Advantages
Simple structure
Easy manufacturing and maintenance
Step feeding and reverse-rotation prevention in one mechanism
Easy application to manual, pneumatic, and mechanical drives
Economical for low-speed and low-frequency systems
8.6 Disadvantages
Impact between teeth and pawl generates noise
Large backlash
Unsuitable for high-speed operation
Wear of ratchet teeth and pawl
Limited precision positioning
Output motion is not smooth
8.7 Typical Applications
Manual winches
Winding devices
Chain tension adjusters
Step-feeding systems
Manual indexing tables
Supply feeders
Anti-reverse mechanisms
9. Intermittent Gears and Incomplete Gears
9.1 Definition
An intermittent gear has teeth formed only on part of its circumference. The output shaft rotates while the toothed sections are engaged and remains stationary during the toothless section.
It is also called an incomplete gear.
9.2 Main Components
Full gear or driving gear
Incomplete output gear
Toothed section
Toothless section
Locking mechanism
Dwell-position device
9.3 Characteristics
Movement angle can be set by the gear ratio
Relatively high torque can be transmitted
Simple structure
Impact may occur at initial tooth engagement
A separate locking device may be required during dwell
9.4 Design Considerations
Impact on the first engaging tooth
Tooth-tip interference
Backlash
Tooth-surface strength
Dwell-position locking
Lubrication
Rotational speed
Gear-manufacturing accuracy
9.5 Typical Applications
Low-speed feeders
Counting devices
Step feeding of packaging material
Simple rotary distribution devices
Educational mechanisms
Low-cost automation systems
10. Escapement Mechanisms
10.1 Definition
An escapement mechanism separates continuously supplied components or products into individual units or defined quantities and releases them to the next process.
It focuses more on controlling product flow than on indexing a rotary shaft.
10.2 Basic Operation
Products are supplied continuously
→ Front stopper holds the first product
→ Rear stopper blocks the following product
→ Front stopper releases
→ First product is discharged
→ Front stopper returns
→ Rear stopper releases
→ Next product advances
10.3 Main Types
Dual-stopper type
Sliding-gate type
Rotary-finger type
Star-wheel type
Cam-driven type
Pneumatic-cylinder type
Servo-separation type
Vacuum-pickup type
10.4 Design Considerations
Product size and shape
Supply pressure
Friction between products
Possibility of product damage
Jamming
Supply speed
Sensor position
Stopper response time
Prevention of double feeding
Cleanability
10.5 Typical Applications
Vibratory feeders
Component supply systems
Bottle and container feeding
Packaging machines
Assembly machines
Inspection equipment
Product-counting devices
11. Star-Wheel Mechanisms
11.1 Definition
A star wheel uses a rotating element with pockets or grooves corresponding to the product shape to separate products at a constant pitch and transport them rotationally.
11.2 Main Functions
Creation of product spacing
Maintenance of product orientation
Transfer of products into a rotary process
Synchronization of infeed and discharge
Product positioning
11.3 Main Components
Star wheel
Central shaft
Product pockets
Guide rails
Infeed screw
Discharge guide
Drive mechanism
Safety guard
11.4 Advantages
Stable separation of containers and products
Easy integration with rotary filling and capping machines
Accurate maintenance of product pitch
Applicable to both continuous and intermittent operation
11.5 Disadvantages
A different star wheel may be required for a product-format change
Sensitive to dimensional variation of the product
Incorrect entry can cause jamming and product damage
Clearance between guides and pockets is critical
11.6 Typical Applications
Bottle fillers
Capping machines
Labeling machines
Container inspection systems
Packaged-product distribution
Food-container transport systems
12. Cam Indexers
12.1 Definition
A cam indexer uses a specially designed cam profile and roller followers to convert continuous input rotation into precise intermittent output rotation.
It can provide smoother acceleration and deceleration than a Geneva mechanism and is suitable for high-speed, high-precision indexing.
12.2 Main Components
Input camshaft
Cam
Turret or output wheel
Cam-follower rollers
Output shaft
Bearings
Housing
Lubrication system
Preload structure
12.3 Operating Principle
As the input cam rotates continuously, the cam profile sequentially drives the rollers on the output turret and rotates the output shaft through the specified angle.
During dwell, the cam profile restrains the output shaft in both directions and provides high positional rigidity.
12.4 Main Characteristics
High positioning repeatability
Smooth acceleration and deceleration
Low backlash
High dwell rigidity
High-speed capability
High output torque
Various index angles
Defined motion profiles
13. Barrel Cam Indexers
13.1 Structure
A spatial curved groove machined on the outer surface of a cylindrical cam engages rollers on the output turret.
13.2 Characteristics
Input and output shafts can be arranged parallel or in another specified orientation
Compact structure
Suitable for high-speed indexing
Precision machining of the cam groove and rollers is critical
13.3 Typical Applications
Assembly machines
Packaging machines
Process transfer systems
Small indexing tables
Component orientation devices
14. Globoidal Cam Indexers
14.1 Structure
A globoidal cam engages multiple rollers arranged circumferentially around the output turret.
14.2 Characteristics
Multiple rollers transmit load sequentially
High torque and dwell rigidity
Backlash can be minimized
Suitable for high-speed, high-load indexing tables
Manufacturing and assembly accuracy are critical
14.3 Typical Applications
Large rotary indexing tables
Automotive component assembly lines
Machine-tool automation
High-speed packaging equipment
Inspection and machining stations
15. Flat Cam Indexers
15.1 Structure
The profile of a flat or disc cam drives rollers on the output turret.
15.2 Characteristics
Relatively easy to understand structurally
Thin and flat construction possible in certain layouts
Suitable for small and medium loads
Cam-profile accuracy and roller preload are important
16. Parallel Cam Indexers
16.1 Structure
Two or more parallel cams drive rollers mounted on the output shaft from both sides.
16.2 Characteristics
Output shaft can be constrained in both directions
High dwell rigidity and low backlash
Relatively high load capacity
Assembly and phase adjustment are critical
17. Roller Gear Cam Indexers
17.1 Definition
A roller gear cam indexer is a precision mechanism in which a cam and multiple rollers engage continuously in a gear-like manner to index the output shaft.
17.2 Characteristics
Predominantly rolling contact
Low friction
High positioning accuracy
High dwell rigidity
Long service life
High-speed operation
Reduced backlash through preload
17.3 Points Requiring Attention
Lubrication condition is critical
Roller-bearing life must be evaluated
Overload impact should be avoided
Cam and roller alignment is important
18. Motion Profiles of Cam Indexers
18.1 Role of the Motion Profile
The motion profile defines how output displacement, velocity, acceleration, and jerk change during the indexing movement.
Even with the same index angle and index time, the motion profile affects:
Maximum velocity
Maximum acceleration
Maximum drive torque
Vibration
Impact
Product movement
Settling time after indexing
Cam and bearing life
18.2 Constant-Velocity Motion
Velocity is maintained at a constant value.
Although conceptually simple, it produces severe impact because velocity changes abruptly at the beginning and end.
It is unsuitable for precision high-speed systems.
18.3 Constant-Acceleration and Deceleration Motion
The output accelerates at a constant rate during the first half of the movement and decelerates at a constant rate during the second half.
It improves upon constant-velocity motion, but jerk may be discontinuous at acceleration-transition points.
18.4 Simple Harmonic Motion
Displacement is generated using sine or cosine relationships.
Velocity and acceleration are relatively smooth, but acceleration may not be zero at the beginning and end of movement.
18.5 Cycloidal Motion
Velocity and acceleration can both be zero at the beginning and end of the movement.
It is widely used for high-speed indexing and is effective in reducing shock and residual vibration.
18.6 Polynomial Motion
Polynomial functions such as 3-4-5 and 4-5-6-7 profiles smoothly connect displacement, velocity, acceleration, and jerk.
They are used in precision servo and cam design.
18.7 Modified Sine and Composite Motion Profiles
Several motion profiles may be combined to optimize load, speed, and settling performance.
19. Velocity, Acceleration, and Jerk
19.1 Average Output Angular Velocity
If the index angle is θ_index and the index time is t_index:
ω_avg = θ_index / t_index
The angle should normally be expressed in radians.
19.2 Actual Maximum Velocity
Actual maximum velocity is greater than average velocity and depends on the motion profile.
Therefore, motors and cams should not be selected based only on average velocity.
19.3 Angular Acceleration
The inertial torque of the output shaft and table is proportional to angular acceleration.
T_inertia = Iα
Where:
T_inertia: Inertial torque
I: Mass moment of inertia of the output assembly
α: Angular acceleration
19.4 Jerk
Jerk is the time rate of change of angular acceleration.
j = dα / dt
High jerk can cause:
Mechanical shock
Vibration
Noise
Product instability
Fastener loosening
Roller and bearing fatigue
Long settling time after indexing
20. Inertia and Drive Torque
20.1 Mass Moment of Inertia
The inertia of a rotary table and its payload is strongly affected not only by mass but also by the distance of the mass from the rotational axis.
The farther the mass is positioned from the axis, the greater the moment of inertia.
20.2 Total Inertia
The total inertia acting on the output shaft includes:
Rotary table
Jigs and fixtures
Products
Output shaft
Couplings
Gears and pulleys
Rotary arms
Output components of the gear reducer
20.3 Required Drive Torque
The required drive torque can be conceptually expressed as:
T_required
= T_inertia + T_friction + T_process + T_disturbance
Where:
T_inertia: Inertial torque
T_friction: Friction torque
T_process: Process torque
T_disturbance: Disturbance and impact torque
20.4 Effect of a Gear Reducer
When a reducer is used, the load inertia reflected to the motor decreases according to the square of the reduction ratio.
However, the following are introduced:
Reducer backlash
Efficiency loss
Torsional elasticity
Additional inertia
Additional maintenance requirements
21. Concepts Related to Accuracy
21.1 Indexing Accuracy
The difference between the commanded or designed target position and the actual stop position.
21.2 Positioning Repeatability
The consistency of the stop position when the system repeatedly moves to the same position under identical conditions.
A system may have good repeatability while still having absolute positioning error.
21.3 Accumulated Pitch Error
The accumulation of individual position errors as the mechanism moves sequentially through multiple index positions.
21.4 Backlash
Mechanical clearance that causes delayed output response when the direction of motion is reversed.
21.5 Lost Motion
Overall input-output lost movement, including not only gear backlash but also:
Cam-to-roller clearance
Bearing clearance
Shaft torsion
Coupling elasticity
Housing deformation
Joint clearance
21.6 Dwell Repeatability
The ability of the output to maintain a stable position during dwell even when process loads are applied.
22. Dwell Rigidity and Locking
22.1 Dwell Rigidity
Dwell rigidity indicates how little the output shaft deflects under external torque while stationary.
Low dwell rigidity can cause:
Position movement during machining
Variation in filling position
Assembly error
Vibration
Product-quality variation
22.2 Mechanical Locking Methods
Double-sided cam constraint
Locking disc
Indexing pin
Tapered locking pin
Hirth coupling
Face-gear clamp
Disc brake
Wedge lock
Toggle lock
22.3 Indexing Pin
After the output table reaches the target position, a precision pin enters a bushing or hole to lock the position.
This provides high accuracy and rigidity, but the following must be reviewed:
Position error before pin insertion
Pin-tip geometry
Bushing wear
Insertion impact
Contamination
Release-confirmation sensor
22.4 Hirth Coupling
Two axially mating discs with radial teeth provide high repeatability and rigidity.
Hirth couplings are used in precision rotary tables and machine tools.
23. Servo Indexing
23.1 Definition
Servo indexing uses servo-motor position control to move an output shaft or table through a desired angle within a defined time.
23.2 Basic Configuration
Servo motor
→ Coupling or gear reducer
→ Output table
→ Encoder feedback
→ Position controller
23.3 Advantages
Index angle can be freely changed
Index and dwell times can be programmed
Product-specific recipes can be applied
Velocity and acceleration profiles can be changed
Forward and reverse rotation are possible
Multiple positions and irregular pitches can be set
Diagnostics and data collection are easy
23.4 Disadvantages
More complex control system
Increased motor and drive cost
Dwell rigidity against external load may be lower than that of a mechanical cam
Reducer backlash may affect positioning
Safety control and a brake may be required
Position-holding measures may be needed during power loss
23.5 Typical Applications
Multi-product assembly machines
Variable-pitch packaging machines
Robotic cells
Inspection tables
Machining-position switching devices
Flexible manufacturing systems
24. Direct-Drive Indexing Tables
24.1 Definition
A direct-drive system uses a torque motor to drive the rotary table directly without a gear reducer.
24.2 Advantages
No reducer backlash
High positioning accuracy
High acceleration and deceleration capability
Fewer mechanical components
Reduced maintenance
Flexible indexing patterns
24.3 Disadvantages
Large torque motor and drive required
Motor heat generation may be significant
Large load inertia acts directly on the motor
Position-holding device may be required during power failure
High-performance control and a precision encoder are required
25. Stepper-Motor Indexing
25.1 Characteristics
A stepper motor rotates by a fixed angle proportional to the number of input pulses, making it easy to use in small indexing devices.
25.2 Advantages
Relatively simple structure and control
Suitable for low-cost positioning
High holding torque at low speed
Suitable for repeated constant-pitch feeding
25.3 Disadvantages
Possibility of missed steps
Reduced high-speed torque
Resonance and vibration may occur
Less smooth than closed-loop servo systems
Limited suitability for high-inertia loads
25.4 Applications
Small rotary tables
Label feeders
Small packaging machines
Component feeders
Simple film-feeding systems
26. Comparison of Mechanical and Servo Indexing
26.1 Mechanical Cam Indexers
Suitable conditions:
High-speed repetitive cycles
Fixed index angle
High dwell rigidity
High repeatability
Mass production
Long-term use with an unchanged process
Advantages:
High mechanical synchronization
High rigidity during dwell
Multiple processes can be synchronized from one main shaft
Stable repeated operation
Disadvantages:
Difficult to change motion conditions
Mechanism replacement may be required for product changes
Precision machining of cams and rollers is required
26.2 Servo Indexing
Suitable conditions:
Frequent product changes
Various index angles
Variable cycles
Irregular position arrangements
Data-based control
Advantages:
Motion can be modified by changing the program
Individual processes can be controlled independently
Easy diagnostics and monitoring
Disadvantages:
More complex control
Dwell rigidity may need to be reinforced separately
Performance is affected by reducers and brakes
26.3 Hybrid Systems
A servo motor may be combined with a mechanical cam or locking device.
Example:
Servo motor
→ Cam indexer
→ Rotary table
Another example:
Servo motor
→ Rotary table
→ Precision indexing pin
→ Mechanical locking during the process
This approach combines servo flexibility with mechanical locking rigidity.
27. Indexing Tables
27.1 Definition
An indexing table is a rotary platform that sequentially moves workpieces between multiple process positions.
27.2 Main Components
Rotary table
Indexing drive
Central shaft
Bearings
Housing
Jigs and fixtures
Locking device
Position sensors
Safety guard
27.3 Table Types
Horizontal rotary table
Vertical dial table
Ring-type indexing table
Hollow rotary table
Lift-and-index table
Precision clamping table
27.4 Main Design Considerations
Table diameter
Number of stations
Payload
Eccentric load
Moment of inertia
Indexing time
Dwell time
Repeatability
Dwell rigidity
Process load
Bearing life
Wiring and piping
28. Linear Indexing Mechanisms
28.1 Definition
A linear indexing mechanism moves products or fixtures stepwise through a fixed linear distance.
28.2 Main Types
Walking beam
Lift-and-carry mechanism
Pallet-chain indexer
Cam-driven linear indexer
Servo belt indexer
Rack-and-pinion indexer
Pneumatic-cylinder indexer
28.3 Walking Beam
Products or pallets are lifted, moved forward, and placed down again.
Basic Sequence
Lift
→ Advance
→ Lower
→ Return
Advantages
Reduces friction during transfer
Provides stable support at process positions
Suitable for fixed-pitch movement
Disadvantages
Linkage and cam structures can be complex
Vertical and horizontal motion must be synchronized
Installation height may increase
28.4 Pallet Indexing Conveyor
Pallets are moved at a fixed pitch using chains, timing belts, or linear modules.
Buffers, stopping devices, and positioning pins may be used together.
29. Position Sensors and Detection
29.1 Home Sensor
Establishes the reference position of the mechanism.
29.2 Index-Complete Sensor
Confirms that the output has reached the target position.
29.3 Lock-Confirmation Sensor
Confirms that an indexing pin or clamp is fully engaged.
29.4 Release-Confirmation Sensor
Confirms that the locking device has been released before table movement.
29.5 Product Detection Sensor
Detects product presence, orientation, and position.
29.6 Torque and Overload Detection
Motor current, torque sensors, or mechanical torque limiters can be used to detect jamming and overload.
30. Overload Protection
30.1 Causes of Overload
Product jamming
Fixture interference
Double product feeding
Locking pin not released
Bearing damage
Foreign matter
Increased process load
Inertial impact during emergency stop
30.2 Protection Methods
Torque limiter
Slip clutch
Shear pin
Servo torque limit
Motor-current monitoring
Mechanical stopper
Shock-absorbing coupling
Safety clutch
30.3 Torque Limiter
When the preset torque is exceeded, the torque limiter interrupts or allows slipping of power transmission between the drive and output.
Automatic-reset and manual-reset types are available.
31. Shock and Vibration
31.1 Main Causes
Abrupt acceleration and deceleration
High jerk
Mechanical backlash
Impact between pin and slot
Poor cam-to-roller contact
Table eccentricity
Uneven product distribution
Insufficient frame stiffness
Resonance
31.2 Reduction Methods
Apply a smooth motion profile
Increase movement time
Reduce output mass
Place mass closer to the rotational center
Apply preload
Increase frame stiffness
Use shock absorbers
Perform dynamic balancing
Improve assembly accuracy
Use damping materials and vibration-isolation mounts
31.3 Settling Time
Settling time is the time required for vibration to decrease to an acceptable level after the output reaches the target position.
Long settling time reduces the dwell period available for the actual process.
32. Bearing and Shaft Design
32.1 Output-Shaft Loads
The output shaft may be subjected to:
Radial load
Axial load
Overturning moment
Eccentric load
Impact load
Repeated load
32.2 Bearing Arrangements
Angular-contact ball bearings
Tapered roller bearings
Cross-roller bearings
Cylindrical roller bearings
Four-point-contact bearings
Turntable bearings
32.3 Hollow Shaft
A hollow output shaft may be used to route wiring, pneumatic hoses, vacuum lines, or sensors through the center of rotation.
The following should be reviewed:
Cable bending
Rotary joints
Slip rings
Pneumatic rotary unions
Waterproofing and washdown
Maintenance access
33. Lubrication and Sealing
33.1 Main Lubrication Points
Cam and roller
Gear engagement
Output-shaft bearings
Geneva pin and slot
Ratchet teeth
Links and bushings
Chains and sprockets
33.2 Lubrication Methods
Oil bath
Grease lubrication
Circulating lubrication
Automatic lubrication
Sealed bearings
Self-lubricating bushings
33.3 Sealing
The following contaminants should be prevented from entering the mechanism:
Dust
Washdown water
Product fragments
Metal particles
Detergent
Corrosive liquids
Typical sealing methods include:
Oil seals
Lip seals
Labyrinth seals
O-rings
Gaskets
Bellows
Sealed housings
34. Materials and Surface Treatment
34.1 Cams
Required characteristics include:
High surface hardness
Contact-fatigue resistance
Wear resistance
Dimensional stability
Applicable materials and treatments include:
Alloy steel
Carburizing
Nitriding
Induction hardening
Precision grinding
34.2 Rollers
Bearing steel
Heat-treated steel
Precision grinding
High-hardness surface
34.3 Geneva Pins and Slots
Materials and surface hardness sufficient to resist impact and bearing pressure are required.
34.4 Tables and Housings
Carbon steel
Cast iron
Aluminum alloy
Stainless steel
Welded frames
Stiffness, vibration damping, weight, and corrosion resistance should be considered together.
35. Selection Procedure for Intermittent and Indexing Mechanisms
35.1 Define the Working Function
Rotary position switching
Linear pitch feeding
Product separation
Film feeding
Pallet transfer
Process dwell
Assembly positioning
Inspection-position switching
35.2 Define Output Requirements
Index angle or travel distance
Number of stations
Indexing time
Dwell time
Cycle speed
Direction of rotation
Positioning repeatability
Dwell rigidity
35.3 Analyze Load Conditions
Payload
Mass moment of inertia
Eccentric load
Process torque
Axial load
Overturning moment
Impact load
Emergency-stop load
35.4 Compare Mechanism Types
Geneva mechanism
Ratchet mechanism
Intermittent gear
Cam indexer
Servo indexer
Direct-drive system
Walking beam
Pneumatic indexing system
35.5 Review Motion Characteristics
Velocity
Acceleration
Jerk
Settling time
Motion profile
Residual vibration
Synchronization
35.6 Review Accuracy
Indexing accuracy
Positioning repeatability
Backlash
Lost motion
Accumulated pitch error
Deflection during dwell
35.7 Review Environmental Conditions
Temperature
Dust
Moisture
Washdown
Corrosion
Food contact
Cleanroom
Vacuum
Explosion hazard
35.8 Review Maintainability
Lubrication access
Cam and roller replacement
Sensor adjustment
Torque-limiter reset
Bearing replacement
Disassembly space
Cleaning
Spare parts
35.9 Final Verification
Motion simulation
Inertia and torque calculation
Structural analysis
Bearing-life calculation
Repeatability testing
Maximum-load testing
Overload testing
Emergency-stop testing
Long-term durability testing
36. Major Failure Modes
36.1 Geneva Mechanism
Driving-pin wear
Slot wear
Slot-edge fracture
Locking-surface wear
Increased backlash
Impact fatigue
Shaft and bearing damage
36.2 Ratchet Mechanism
Ratchet-tooth wear
Pawl-tip fracture
Spring fatigue
Reverse rotation
Tooth skipping
Shaft clearance
Increased impact noise
36.3 Cam Indexer
Cam-surface pitting
Roller-bearing damage
Scoring between cam and roller
Reduction in preload
Increased backlash
Insufficient lubrication
Output-shaft bearing damage
Housing deformation
36.4 Servo Indexer
Encoder error
Increased reducer backlash
Motor overheating
Coupling loosening
Brake wear
Improper control parameters
Communication error
Missed steps or position-following error
36.5 Common Causes of Failure
Overload
Product jamming
Insufficient lubrication
Contamination
Shaft misalignment
Excessive acceleration
Insufficient frame stiffness
Bearing life exceeded
Assembly error
Sensor malfunction
37. Maintenance and Inspection
37.1 Daily Inspection
Abnormal noise
Vibration
Temperature rise
Lubricant leakage
Change in repeat positioning
Change in cycle time
Sensor operation
Locking-device operation
Product jamming
Safety-guard condition
37.2 Periodic Inspection
Cam and roller contact surfaces
Geneva pin and slots
Ratchet teeth
Output-shaft clearance
Bearing condition
Coupling fastening
Torque limiter
Brake
Indexing pin and bushing
Table levelness
37.3 Accuracy Inspection
Position error at each station
Positioning repeatability
Accumulated pitch error
Shaft runout
Table runout
Deflection during dwell
Backlash
37.4 Condition-Based Maintenance
The following monitoring methods may be used:
Vibration
Temperature
Motor current
Drive torque
Encoder position error
Cycle time
Lubricant condition
Noise
Bearing-frequency analysis
38. Safety Design
38.1 Pinch and Collision Hazards
Pinch and shear points are created between the indexing table and fixed frame.
Required protective measures include:
Fixed guards
Interlocked doors
Safety distances
Light curtains
Safety scanners
Emergency stops
Safe-speed control
Torque limitation
38.2 Unexpected Restart
The machine must not restart unexpectedly after a product jam is removed or a sensor is restored.
38.3 Stored Energy
The following stored energy may remain in the system:
Rotational inertia
Compressed air
Hydraulic pressure
Springs
Vertical loads
Brake-release energy
38.4 Maintenance Lockout
During maintenance, electrical, pneumatic, hydraulic, and gravitational energy must be isolated and the mechanism mechanically locked.
39. Intermittent and Indexing Mechanisms in Food Machinery
In food machinery, hygienic design, cleanability, corrosion resistance, and lubricant-contamination prevention must be considered together with indexing performance.
39.1 Main Hygienic Requirements
Structure that prevents food-residue accumulation
Open and washable construction
Minimized deep crevices
Minimized horizontal surfaces
Drainable surfaces
Separation of lubricated areas from food zones
Sealed housings
Corrosion-resistant materials
Easy drying after washdown
Tool-less replaceable format parts
39.2 Cam Indexers
Because cams and rollers require lubrication, they should be installed inside sealed housings and separated from food zones.
39.3 Star Wheels
Because star wheels contact products directly, the following should be considered:
Food-grade plastics or stainless steel
Tool-less replacement
Open pockets
Washable guides
Drainable structure
Prevention of product damage
39.4 Escapement Mechanisms
The structure should be simplified so that product residue does not accumulate around the stoppers.
The exhaust direction of pneumatic devices should also be arranged so that exhaust air does not directly contact food.
39.5 Chains and Ratchets
Exposed lubricated chains and ratchets should be avoided in direct food zones whenever possible and placed in a separate drive area or hygienic enclosure.
39.6 Typical Applications
Indexing containers to filling positions
Distribution of meat-processing products
Tray feeding
Intermittent packaging-film feeding
Dwell positioning for sealing and cutting
Product inspection tables
Container capping
Product discharge distribution
Label positioning
40. Application Examples
40.1 Rotary Filler Indexing Table
Servo motor or cam indexer
→ Rotary table
→ Container fixtures
→ Filling position
Main considerations:
Number of stations
Index angle
Filling dwell time
Liquid sloshing
Table inertia
Cleanability
Container detection
Overflow prevention
40.2 Intermittent Packaging-Film Feeding
Servo motor
→ Feed rollers
→ Packaging film
→ Sealing and cutting position
Main considerations:
Film-feed pitch
Tension
Registration-mark sensor
Slippage
Acceleration
Film elongation
Stop-position accuracy
40.3 Automatic Assembly Indexing Table
Geared motor
→ Cam indexer
→ Rotary table
→ Multiple assembly stations
Main considerations:
Process time
Maximum process load
Fixture repeatability
Dwell rigidity
Overload protection
Operator safety
Defective-product discharge
40.4 Product Escapement
Vibratory feeder
→ Dual stoppers
→ Single-product release
→ Supply to assembly position
Main considerations:
Product overlap
Supply pressure
Stopper wear
Product damage
Sensor position
Pneumatic response time
Jam recovery
40.5 Star-Wheel Container Transfer
Infeed screw
→ Star wheel
→ Filling or capping process
→ Outfeed star wheel
Main considerations:
Container pitch
Pocket geometry
Guide clearance
Product-change flexibility
Tool-less replacement
Synchronization
Cleanability
40.6 Walking-Beam Transfer System
Cam or servo drive
→ Lift
→ Advance
→ Lower
→ Return
Main considerations:
Transfer pitch
Pallet weight
Lifting height
Positioning
Link interference
Cycle speed
Fall prevention
41. Analysis Tools for Intermittent and Indexing Mechanisms
41.1 CAD Motion Analysis
The following can be evaluated:
Range of motion
Interference
Velocity
Acceleration
Jerk
Joint reaction forces
Dwell time
Product trajectory
41.2 Multibody Dynamic Analysis
Table inertia
Cam-to-roller contact force
Bearing load
Drive torque
Impact
Vibration
41.3 Finite-Element Analysis
Cam contact stress
Turret deformation
Output-shaft strength
Housing stiffness
Table deformation
Natural frequency
Fatigue life
41.4 Control Simulation
For servo indexers, the following can be reviewed:
Position-following error
Velocity profile
Peak torque
Settling time
Resonance
Control gains
Emergency-stop response
42. Conclusion
An intermittent mechanism converts continuous input motion into repeated movement and dwell. An indexing mechanism moves the output to a defined position and then holds it securely.
Geneva mechanisms are simple and economical, but impact and vibration can become significant at high speed. Ratchet-and-pawl mechanisms are suitable for step feeding and reverse-rotation prevention, but they have limitations in precision and high-speed performance. Star wheels and escapement mechanisms are effective for product separation and constant-pitch feeding.
Cam indexers provide smooth acceleration and deceleration according to a defined motion profile and can achieve high repeatability and dwell rigidity. They are therefore suitable for high-speed packaging machines, automatic assembly systems, and precision rotary tables.
Servo indexing allows the index angle, movement time, and motion profile to be changed through programming, making it advantageous for flexible automation and multi-product production. However, where high dwell rigidity is required, indexing pins, brakes, or mechanical clamps may need to be added.
Intermittent and indexing mechanisms should be designed and selected according to the following sequence:
Define the working function
→ Determine the index angle or travel distance
→ Determine the number of stations and cycle time
→ Allocate indexing time and dwell time
→ Calculate load and inertia
→ Select the mechanism type
→ Review the motion profile and acceleration characteristics
→ Calculate drive torque and bearing loads
→ Review positioning accuracy and dwell rigidity
→ Design overload protection and safety measures
→ Review lubrication, maintainability, and hygienic design
→ Perform simulation and durability testing
A properly designed intermittent or indexing mechanism is a key component for improving machine productivity, positioning accuracy, process synchronization, operational stability, and maintainability.