A therapy robot does not sell a robot arm; it sells a force applied to a human body. Pressure, rhythm and depth are the prescription, and position control cannot deliver them: soft tissue is compliant and time-varying, so one position command yields contact forces that differ several-fold between muscle and bone. Force-controlled harmonic joint modules turn contact force into a closed-loop variable - the only way to make dose repeatable, human contact safe and a therapist's technique teachable. Starting from one site photo of a bedside therapy robot, this article reads the configuration, sets out five reasons force control is unavoidable, settles HONPINE's TCHL-versus-HAG choice criterion by criterion, and gives the torque sensor resolution budget that picks the frame sizes.

In lithium battery plants, reducer selection for a robotic arm is not about finding one "best" gearbox — it is about dividing work by joint. RV reducers take the shoulder and elbow (J1–J3), where stiffness, shock resistance, and long life matter most; harmonic reducers take the wrist (J4–J6), where near-zero backlash, high torque density, and low weight decide positioning accuracy. Planetary gearboxes cover long-travel Cartesian transfer at lower cost. Lithium battery production then adds three stricter filters: extreme repeatability (±0.02–0.05 mm), 24/7 high-duty cycles, and zero tolerance for metal particle contamination. This guide explains the logic behind joint-by-joint selection, compares the three reducer types, and maps typical configurations for every station.

Collaborative robot joints must balance several competing requirements: high torque, compact size, low weight, precise positioning, fast response and responsive force interaction. This makes the choice of transmission architecture particularly important, especially as cobots are being designed for more dynamic motion and increasingly demanding human-robot interaction. Two approaches are often considered for this type of application: the DD motor (direct-drive motor) and the harmonic reducer combined with a servo motor. A DD motor eliminates the mechanical reduction stage and provides a direct connection between the motor and joint output, while a harmonic reducer uses a high-ratio precision transmission to achieve high output torque from a compact motor.