Fixed-Sequence Robot

A Fixed-Sequence Robot, also known as a pre-programmed robot or hard-wired robot, is a type of industrial robot that performs a predetermined series of operations in a specific order. The sequence of movements and tasks is fixed and cannot be easily altered once programmed. Such robots are primarily used in mass production environments where the same set of operations must be repeated continuously with precision and consistency.
Fixed-sequence robots are among the earliest and simplest forms of automation, representing the first generation of industrial robotics.

Definition

A Fixed-Sequence Robot is a mechanical device designed to execute a predetermined set of movements based on a fixed control programme. The sequence of actions — such as picking, placing, welding, assembling, or packaging — is established at the time of programming or installation.
The robot follows this sequence repeatedly without deviation unless the hardware or control system is physically modified or reprogrammed.

Characteristics of Fixed-Sequence Robots

• Predefined Motion Path: The robot follows a specific sequence of operations that remains constant.
• Limited Flexibility: Any change in the sequence requires manual adjustment or reprogramming.
• High Repeatability: Performs repetitive tasks with precision and uniformity.
• Simple Control System: Operates through mechanical cams, switches, or basic controllers.
• Suitable for High-Volume Production: Ideal where product design and process remain unchanged for long periods.
• Low Cost and Maintenance: Simple design reduces operational complexity and maintenance requirements.

Components

A typical fixed-sequence robot consists of the following elements:

1. Manipulator or Arm:
   • The mechanical structure that performs physical tasks like movement, lifting, or assembly.
2. End Effector:
   • The tool or device attached to the robot arm (e.g., gripper, welding gun, or suction pad).
3. Actuators:
   • Devices (electric, hydraulic, or pneumatic) that drive the robot’s movement.
4. Controller:
   • The control unit that governs the order, timing, and coordination of the robot’s operations.
5. Sensors:
   • Limited sensing elements (if any) to detect positions or simple conditions like object presence.

Working Principle

The working of a fixed-sequence robot is based on a predefined control programme that dictates its movement and operation order.

1. The control system stores the sequence of actions, such as movement paths, tool activation, and timing.
2. Once started, the robot executes each action step-by-step in a fixed order.
3. The system repeats the sequence continuously until stopped or reconfigured.

Example:In an automobile assembly line, a fixed-sequence robot might perform tasks such as:

1. Picking up a car door panel.
2. Moving it to the welding station.
3. Performing spot welds at specific points.
4. Returning to the start position.This cycle repeats identically for every unit produced.

Applications

Fixed-sequence robots are ideally suited to tasks that are highly repetitive and predictable. Common applications include:

• Assembly Line Operations: Repetitive mechanical assembly of parts.
• Material Handling: Transferring components between machines or conveyor belts.
• Welding and Painting: Performing the same patterns or strokes on identical products.
• Packaging and Palletising: Placing items into boxes or stacking them in fixed arrangements.
• Machining and Die-Casting: Loading and unloading machine tools in a fixed pattern.

In sectors like automotive manufacturing, electronics, and consumer goods, fixed-sequence robots are integral to automation lines where process consistency is critical.

Advantages

• High Speed and Efficiency: Performs repetitive operations rapidly without human fatigue.
• Precision and Consistency: Maintains uniform quality in mass production tasks.
• Low Operating Cost: Once installed, operation and maintenance costs are minimal.
• Reliability: Simple mechanical and control systems make it dependable for long-term use.
• Reduced Human Intervention: Minimises labour dependency and human error.

Limitations

Despite their efficiency, fixed-sequence robots have several constraints:

• Lack of Flexibility: Cannot adapt to new tasks or design changes without reprogramming or mechanical modification.
• High Setup Cost: Initial design and installation may be expensive due to customisation.
• Limited Sensing Capability: Operates effectively only in structured environments with minimal variability.
• Obsolescence Risk: Becomes outdated when product designs or processes change frequently.
• No Decision-Making Ability: Lacks intelligence or adaptability to respond to unexpected conditions.

Comparison with Other Types of Industrial Robots

Fixed-sequence robots are thus best suited for stable production systems where changes are infrequent, whereas modern intelligent robots cater to dynamic and flexible operations.

Role in Industrial Automation

Fixed-sequence robots represent the first generation of industrial automation. They introduced mechanisation into manufacturing by replacing repetitive human tasks with programmed mechanical precision. Although technologically simple, their contribution to productivity and cost reduction was foundational to the evolution of modern robotics.
They continue to be used in legacy systems, high-volume assembly lines, and process industries where flexibility is less critical than efficiency.

Evolution and Modern Relevance

With advances in robotics and artificial intelligence, many industries have transitioned from fixed-sequence to programmable and adaptive robots. However, fixed-sequence robots remain relevant in:

• Continuous production environments like bottling plants and automotive assembly.
• Applications requiring extreme precision in repetitive tasks.
• Low-cost automation systems in small and medium enterprises (SMEs).