What Is Robot Cycle Time and How Can It Be Reduced?

Robot cycle time is an important factor when evaluating the productivity of an automated production process.

A robot may have a high maximum speed, but that does not necessarily mean the complete application has a short cycle time. Robot movement, gripper operation, workpiece positioning, machine processing, waiting time, and other equipment all affect how quickly one complete production cycle can be finished.

Understanding these factors is important when selecting a robot or improving an existing automation system.

Robot cycle time is the time required for a robot or automated workstation to complete one defined production cycle and return to the starting condition.

For example, a pick-and-place application may include:

1. Move to the workpiece

2. Close the gripper

3. Pick up the workpiece

4. Move to the destination

5. Place the workpiece

6. Open the gripper

7. Return to the starting position

The time required to complete this sequence contributes to the cycle time.

In a machine tending application, the complete cycle may also include machine door operation, workpiece loading, machining, unloading, and communication with other equipment.

1. Robot Movement

Robot speed and acceleration affect how quickly the arm can move between positions.

However, maximum speed is only one part of the calculation. A robot may spend significant time accelerating, decelerating, changing direction, or waiting for another device.

2. Robot Path

An inefficient path can add unnecessary movement.

If the robot travels farther than necessary between the pickup and placement positions, the cycle becomes longer.

Optimizing the robot path can reduce unnecessary travel while maintaining safe clearance from equipment and workpieces.

3. Gripper Operation

The gripper also contributes to the cycle.

Opening and closing time, gripping confirmation, workpiece stability, and communication between the gripper and robot controller can all affect the overall sequence.

A gripper that is too slow for the application may become a bottleneck.

4. External Equipment

Robot cycle time is often affected by equipment outside the robot.

Examples include:

• CNC machines

• Conveyors

• Fixtures

• Positioners

• Sensors

• Machine doors

• Pallet systems

• PLC-controlled equipment

If the robot has to wait for another device, increasing robot speed alone will not solve the problem.

5. Workpiece Handling

The size, weight, shape, and orientation of the workpiece can influence robot movement and gripping.

Heavy or difficult-to-handle parts may require slower acceleration and more controlled movement.

The workpiece loading position should also be considered when designing the workstation.

1. Optimize the Robot Program

Review the robot's movement sequence and identify unnecessary movements.

Shorter paths can reduce travel time, but the robot should not simply move faster everywhere. The program needs to balance speed, positioning accuracy, equipment clearance, and safe operation.

2. Reduce Waiting Time

Waiting can be a major source of lost production time.

Check whether the robot is waiting for:

• Machine doors

• Sensors

• Fixtures

• PLC signals

• Conveyors

• Processing equipment

Improving communication between devices can sometimes reduce cycle time without changing the robot itself.

3. Select an Appropriate Gripper

The gripper should match the workpiece and required production speed.

Fast and reliable gripping can reduce the time spent picking and releasing parts.

For some applications, a dual gripper can allow the robot to handle two related operations in one movement sequence, potentially reducing unnecessary travel and machine waiting.

4. Improve Workpiece Positioning

Consistent workpiece positioning makes robot movement more predictable.

Fixtures, trays, conveyors, and part presentation systems should be arranged so the robot can access the workpiece efficiently.

Poor positioning can force the robot to make additional movements or use slower approaches.

5. Coordinate the Complete Workstation

The robot should not be optimized independently from the rest of the system.

For example, if a CNC machine requires significantly more time to process a part than the robot needs to load and unload it, increasing robot speed may have little effect on overall production output.

The complete workstation should therefore be analyzed as one process.

6. Choose the Right Robot

Robot selection should be based on the required production cycle rather than maximum speed alone.

Consider:

• Payload

• Reach

• Repeatability

• Motion range

• Acceleration

• Required cycle time

• Gripper

• Workpiece handling method

An oversized robot may increase equipment cost without providing a meaningful production advantage.

It is tempting to assume that a faster robot will automatically increase production output.

In reality, production speed is limited by the slowest important step in the process.

For example, if a robot completes a loading movement in 8 seconds but the machine requires 45 seconds to process the workpiece, reducing robot movement to 6 seconds may have little effect on the total production cycle.

This is why cycle-time improvement should focus on the entire production sequence.

Before purchasing an industrial robot, prepare the complete process information.

Useful information includes:

• Workpiece weight and dimensions

• Pickup and placement positions

• Required production quantity

• Machine processing time

• Required robot movements

• Gripper type

• Fixture layout

• Conveyor speed

• Machine interface

• Target cycle time

A supplier or system integrator can then evaluate the robot, gripper, layout, and peripheral equipment as one automation system.

Robot cycle time is more than the time required for the robot arm to move from one point to another. It represents the interaction between the robot, tooling, workpiece, machine, controls, and other equipment in the production cell.

To reduce cycle time effectively, manufacturers should first identify where time is actually being lost. Optimizing robot paths, reducing waiting periods, improving gripping, and coordinating peripheral equipment can often deliver better results than simply selecting a faster robot.

For new automation projects, cycle time should be considered from the beginning of robot selection and system design.