How a Rotary cam Indexer Works: Cam Profiles, Index Angle and Dwell Explained
Updated: 4 hours ago
A Rotary cam Indexer is a precision mechanical motion-control device designed to convert continuous rotary motion into accurate, repeatable intermittent movement. It is widely used in industrial automation where a workpiece, fixture, tooling plate, or rotary table needs to move from one predetermined position to another and remain stationary for a specific operation.
Unlike a conventional gearbox, which continuously rotates its output shaft, a rotary cam indexer produces a controlled sequence of indexing and dwell. The output moves through a defined angular distance, decelerates smoothly, stops at the required position, and remains stationary before starting the next indexing movement.
This combination of cam profile, index angle, index time, and dwell makes rotary cam indexers particularly suitable for high-speed and repetitive automation applications such as assembly machines, machining systems, inspection equipment, packaging machines, welding systems, and rotary transfer machines.
Understanding how a rotary cam indexer works is important when selecting the correct indexer for an application.
What Is a Rotary cam Indexer?
A rotary cam indexer is a mechanical indexing mechanism consisting of a specially designed cam, follower system, output shaft or flange, bearings, housing, and input drive mechanism.
The input shaft is normally connected to a motor or gearmotor. As the input shaft rotates continuously, the cam profile controls the movement of the followers. This follower movement is transferred to the output mechanism, producing precise intermittent rotary motion.
The output therefore follows a predetermined motion pattern:
Acceleration → Indexing → Deceleration → Stop → Dwell → Next Index
The major advantage is that the required motion is generated mechanically by the cam profile. Once the indexer is correctly selected and driven at the required speed, the output follows the designed motion cycle repeatedly.
This makes CAM rotary indexers particularly useful for applications where the same motion must be repeated thousands or millions of times.
How Does a Rotary cam Indexer Work?
The operating principle of a rotary cam indexer is based on the relationship between the input cam and the output follower mechanism.
The motor rotates the input shaft. The cam mounted on the input shaft rotates along with it. Because the cam has a carefully calculated profile, the follower moves according to the required motion law.
The follower movement causes the output shaft or flange to rotate through a predetermined angle.
For example, consider a rotary table with eight stations. The table may need to move 45° from one station to the next.
The sequence can be represented as:
45° Index → Stop → Dwell → 45° Index → Stop → Dwell
The motor can continue rotating the input shaft while the output shaft alternates between movement and stationary periods.
During the dwell period, the rotary table remains stationary and the machine can perform its required operation.
For example:
The table indexes to the next station.
The table reaches the required position.
The output stops.
The machine performs drilling or assembly.
The dwell period continues.
The next indexing movement begins.
This process repeats continuously throughout the machine cycle.
Understanding the CAM Profile
The cam profile is the heart of a mechanical rotary cam indexer.
It determines how the output moves during the indexing cycle. A cam profile is designed not only to achieve the required angular movement but also to control the motion characteristics of the output.
Important motion characteristics include:
Displacement
Velocity
Acceleration
Deceleration
Jerk
Indexing time
Smoothness of movement
The cam profile has a direct influence on the mechanical performance of the indexer.
A poorly matched motion profile can result in excessive acceleration, vibration, mechanical shock, noise, and increased component loading. A properly designed profile provides smooth and controlled movement while maintaining the required indexing performance.
Therefore, cam profile selection is especially important in high-speed applications.
Acceleration and Deceleration in a Cam Indexer
During an indexing movement, the output shaft cannot instantly move from zero speed to maximum speed.
The cam profile controls the acceleration phase.
At the beginning of the index, the output starts moving from the stationary position. The velocity increases progressively until the output reaches the required operating speed.
As the output approaches the destination position, the cam profile controls the deceleration.
The output gradually slows down and reaches zero velocity at the required indexing position.
The basic motion can therefore be represented as:
Start → Acceleration → Maximum Velocity → Deceleration → Stop
This controlled movement helps reduce shock and vibration and allows the rotary table to reach the required position repeatedly.
What Is Index Angle?
The index angle is the angular distance through which the output shaft rotates during one indexing movement.
For example, if a rotary table moves 30° from one station to the next, the index angle is 30°.
The number of indexing positions can be calculated using:
Number of Stops = 360° ÷ Index Angle
For example:
Number of Positions | Index Angle |
4 | 90° |
6 | 60° |
8 | 45° |
10 | 36° |
12 | 30° |
16 | 22.5° |
20 | 18° |
Therefore, if an application requires 20 equally spaced positions:
360° ÷ 20 = 18°
The required index angle is therefore 18°.
Index angle is one of the fundamental parameters required when selecting a rotary cam indexer.
What Is Dwell in a Rotary cam Indexer?
Dwell is the period during which the output shaft remains stationary while the input cam continues to rotate.
This is an important feature of a CAM rotary indexer because it allows the machine to perform a process while the workpiece remains accurately positioned.
For example, in an automated assembly machine, the rotary table may index to a station and remain stationary while a component is inserted.
The sequence becomes:
Index → Stop → Dwell → Index → Stop → Dwell
The dwell period can be used for operations such as:
Assembly
Drilling
Welding
Inspection
Filling
Screw tightening
Labelling
Pick-and-place
Testing
The required dwell time depends on how long the machine process takes at each station.
Index Time vs Dwell Time
Index time and dwell time are two different parameters.
Index Time:
Index time is the time required for the output shaft to move from one position to the next.
For example:
Index angle = 45°Index time = 0.5 seconds
The output takes 0.5 seconds to complete the 45° indexing movement.
Dwell Time:
Dwell time is the time for which the output remains stationary before the next indexing movement.
For example:
Index time = 0.5 secondsDwell time = 1.5 seconds
The approximate cycle time is:
Cycle Time = Index Time + Dwell Time
Therefore:
Cycle Time = 0.5 + 1.5 = 2 seconds
The machine completes one indexing cycle every two seconds.
Why Is Dwell Important in Automation?
Dwell allows different operations to be performed at different stations of a rotary machine.
Consider a six-station assembly machine.
Each station may perform a different operation:
Station 1: Component loading
Station 2: Drilling
Station 3: Assembly
Station 4: Screw tightening
Station 5: Inspection
Station 6: Unloading
The rotary table indexes from one station to the next and remains stationary during the process.
This allows multiple operations to take place in sequence while maintaining a predictable production cycle.
The dwell period therefore plays an important role in determining the overall productivity of the machine.
Cam Profile and Jerk
In high-speed indexing applications, acceleration alone is not sufficient to evaluate the motion profile.
Jerk, which is the rate of change of acceleration, is also important.
Sudden changes in acceleration can generate mechanical shock and vibration.
A properly designed cam motion law controls the transition between acceleration and deceleration to achieve smoother movement.
This can help reduce:
Vibration
Mechanical shock
Noise
Bearing loading
Wear
Product movement during indexing
For this reason, different cam motion laws may be selected depending on the application requirements.
Effect of Reducing Index Time
Reducing index time can increase machine productivity, but it also changes the mechanical requirements.
If the same angular movement must be completed in a shorter period, the output generally needs to accelerate and decelerate more rapidly.
This can increase:
Acceleration
Inertial forces
Torque requirements
Bearing loads
Mechanical stress
Vibration
Therefore, simply specifying a shorter index time does not automatically mean that every indexer can achieve it.
The indexer must be selected based on the complete application conditions.
Load and Moment Considerations
The weight of the rotary table and workpiece is not the only factor that should be considered when selecting a CAM rotary indexer.
The position of the load relative to the output shaft is also important.
A load located far away from the output center can create a significant moment load.
This is particularly important for large rotary tables and applications where fixtures or workpieces extend significantly from the indexer's output center.
Applications of Rotary cam Indexers
Rotary cam indexers are used across many industries and automation systems.
Typical applications include:
Assembly Automation
Rotary indexing tables can move components between multiple assembly stations.
Machining Automation
Cam Indexers can position components for drilling, tapping, milling, and other machining processes.
Inspection Systems
The rotary table can move components through multiple inspection stations.
Packaging Machinery
Indexing mechanisms can position containers or packages for filling, sealing, labelling, or inspection.
Welding Automation
Components can be accurately positioned at welding stations.
Pick-and-Place Systems
The indexer can present workpieces to robotic or automated handling equipment.
Testing Machines
Multiple testing operations can be performed at different rotary stations.
Transfer Machines
Cam indexing systems can transfer components between sequential manufacturing operations.
Advantages of Rotary Cam Indexers
Rotary cam indexers offer several advantages for industrial automation.
High Repeatability
The mechanical cam profile provides consistent movement from cycle to cycle.
High-Speed Operation
Cam mechanisms are well suited to repetitive high-speed indexing applications.
Smooth Motion
Properly designed cam profiles can provide controlled acceleration and deceleration.
Mechanical Reliability
The mechanical indexing mechanism can operate repeatedly in demanding industrial environments.
Simple Drive Arrangement
A Rotary cam indexer can often operate with a continuously rotating motor or gearmotor without requiring complex electronic positioning for every index.
Suitable for Repetitive Production
Applications with fixed indexing requirements can benefit significantly from mechanical indexing.
Rotary cam Indexer Maintenance
Although rotary cam indexers are designed for reliable operation, appropriate maintenance is important for long service life.
Maintenance requirements depend on the indexer design and manufacturer recommendations but may include:
Lubrication inspection
Checking mounting bolts
Inspecting the drive arrangement
Checking for abnormal noise
Monitoring vibration
Checking for excessive backlash or positioning changes
Inspecting connected components
Following the manufacturer's lubrication and maintenance schedule
The indexer should also be operated within its specified load, speed, moment, and duty-cycle limits.
Conclusion
A Rotary cam Indexer provides a reliable and precise method of producing intermittent rotary motion in automated machinery. Its operation depends on the carefully engineered relationship between the cam profile, index angle, index time, acceleration, deceleration, and dwell.
The cam profile determines how the output moves, while the index angle determines how far it moves during each cycle. The dwell period then provides the stationary time required for assembly, machining, inspection, welding, packaging, or other machine operations.
For an efficient indexing system, it is important to evaluate the complete application rather than selecting an indexer based only on the number of positions or the workpiece weight. Index time, dwell time, load, moment load, rotational inertia, accuracy, speed, mounting orientation, and duty cycle should all be considered.
When correctly selected, a rotary cam indexer can provide smooth, repeatable, high-speed and mechanically synchronized motion, making it an effective solution for a wide range of industrial automation and rotary indexing applications.
For applications where precise and repetitive rotary positioning is required, understanding the fundamentals of Cam profiles, index angles and dwell is the first step toward selecting the right indexing mechanism.
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