A robot arm is a machine designed to move objects with speed, accuracy, and repeatability. It is built from rigid links connected by joints, similar to how a human arm has bones and moving joints. In factories, robot arms can pick up parts, weld metal, sort packages, or assemble products.
Understanding how a robot arm works helps students connect physics, engineering, coding, and real-world automation.
Each joint is moved by a motor or actuator that turns or slides part of the arm. Sensors measure position, speed, and sometimes force so the controller can guide the arm along a planned path. The end effector, such as a gripper, is the tool at the end that interacts with the object.
In a pick-and-place task, the controller moves the gripper to the block, closes it, lifts the block, follows a path, and releases it at a new location.
Key Facts
- A robot arm is made of links and joints, where links are rigid parts and joints create motion.
- Degrees of freedom, or DOF, count the independent ways a robot can move, such as rotating at the base or bending at the elbow.
- Speed = distance/time, so moving a gripper 0.60 m in 2.0 s gives speed = 0.30 m/s.
- Torque = force x lever arm, so a larger load or longer arm requires more turning force at a joint.
- Work = force x distance, so lifting a 10 N block by 0.50 m requires 5.0 J of work.
- Feedback control compares the target position with the measured position and adjusts the motors to reduce error.
Vocabulary
- Joint
- A joint is a movable connection between robot arm links that allows rotation or sliding.
- Link
- A link is a rigid section of a robot arm that connects one joint to another.
- End effector
- An end effector is the tool at the end of a robot arm, such as a gripper, suction cup, or welder.
- Degrees of freedom
- Degrees of freedom are the independent movements a robot can make to position and orient its end effector.
- Actuator
- An actuator is a device, usually a motor or cylinder, that produces motion in a robot joint.
Common Mistakes to Avoid
- Confusing links with joints, which is wrong because links are the solid arm sections while joints are the moving connections between them.
- Counting every visible part as a degree of freedom, which is wrong because a degree of freedom only counts an independent controlled motion.
- Ignoring torque when a block is far from the base, which is wrong because the same block creates more turning effect when the lever arm is longer.
- Assuming the gripper moves in a straight line automatically, which is wrong because the controller must coordinate several joints to create a smooth path.
Practice Questions
- 1 A robot gripper moves 1.2 m from a pickup point to a drop-off point in 3.0 s. What is its average speed?
- 2 A joint must lift a block with a weight of 18 N at a distance of 0.40 m from the joint. What torque is needed, using torque = force x lever arm?
- 3 A robot arm has a rotating base, shoulder joint, elbow joint, wrist bend, and wrist twist. Explain why more degrees of freedom can help the gripper pick up a block from different angles.