What Are Robots?

Robots are programmable machines capable of executing physical tasks with some degree of autonomy, typically by sensing the environment, processing sensory data, and actuating joints or end-effectors in response. The term encompasses a wide range of physical architectures, from rigid serial-link manipulator arms fixed to a factory floor to soft continuum structures inspired by biological organisms to legged and wheeled platforms that navigate unstructured terrain. What unites them is the combination of physical agency in the world, programmability, and varying capacity to act without continuous human direction.

Robots draw their conceptual lineage from mechanical automata and teleoperators developed in the mid-twentieth century, but the modern robot is defined by digital computation and feedback control. The first programmable industrial robot, the Unimate, was installed on a General Motors assembly line in 1961, and the subsequent decades saw rapid development of serial-link kinematic structures, servo control, and, eventually, onboard intelligence.

Mechanical Structure and Actuation

A robot's mechanical structure determines its range of motion and the forces it can apply. Serial-link manipulators chain rigid links through revolute or prismatic joints, with the joint count establishing the degrees of freedom. Six-degree-of-freedom arms can reach arbitrary positions and orientations within their workspace, making them the standard architecture for assembly, welding, and painting tasks. Parallel kinematic machines, such as the delta robot, connect the end-effector to the base through multiple independent kinematic chains, achieving very high speeds and stiffness at the cost of a smaller workspace.

Actuation translates electrical or pneumatic energy into joint motion. Servo motors with optical encoders dominate in industrial manipulators because they provide precise, repeatable position control. Hydraulic actuators supply higher force-to-weight ratios and are used in heavy construction and military systems. Soft actuators, including pneumatic artificial muscles, shape memory alloys, and dielectric elastomers, are employed in soft robots, enabling compliant interactions with fragile objects and biological tissue.

Biologically Inspired Design

Bionics and biomimicry have produced a growing class of robots whose morphology and locomotion are modeled on living organisms. The PMC review of biology and bioinspiration in soft robotics documents how plants and animals provide actuation and sensing strategies that engineered systems struggle to match: the Venus flytrap's bistable snap-through, the octopus's hydrostatic muscular arm, and the mammalian skin's sensitivity to forces as low as 10 pascals. Artificial muscles made from liquid crystal elastomers and dielectric elastomers attempt to replicate the work density of biological muscle.

Legged robots take inspiration from insect and mammalian gaits to traverse stairs, rubble, and soft terrain that wheeled platforms cannot navigate. Quadruped robots such as Boston Dynamics' Spot use reinforcement-learned locomotion controllers that generalize across terrain variations. Aquatic robots model fish and jellyfish propulsion to achieve low-noise, energy-efficient underwater movement.

Sensing and Onboard Intelligence

A robot's sensors determine what it can perceive and therefore what tasks it can perform autonomously. Proprioceptive sensors (encoders, IMUs, force-torque sensors) measure the robot's own state; exteroceptive sensors (cameras, lidar, ultrasonic, tactile arrays) measure the environment. The Nature paper on design, fabrication and control of soft robots identifies sensing and closed-loop control as the two critical capabilities that separate passive soft mechanisms from true soft robots.

Onboard computing, once a significant size and power constraint, has become compact enough to support real-time planning and perception on mobile platforms. Assembly systems that integrate robots with conveyors, vision inspection, and part feeders represent a mature class of application in which sensing, planning, and actuation are tightly coordinated within a larger production architecture. The IEEE Robotics and Automation Society publishes ongoing research on robot design, sensing, and intelligence across multiple peer-reviewed transactions.

Applications

Robots have applications in a wide range of fields, including:

• Manufacturing assembly systems, including welding, painting, and electronics assembly
• Medical surgery and rehabilitation, using both rigid and soft robotic systems
• Exploration, including planetary rovers and deep-sea autonomous underwater vehicles
• Agriculture, including harvesting, pruning, and precision spraying robots
• Disaster response and hazardous environments, where robots substitute for human workers exposed to danger