Domain Adoption: Robotics History and Control Systems Engineering
Target Review Group: Robotics and Cybernetics Engineers/Historians
Abstract:
This material profiles the historical development and underlying control philosophy of the "Belgrade Hands," a series of pioneering robotic prosthetics originating from the Mihajlo Pupin Institute in Yugoslavia, led by Rajko Tomović beginning in the 1960s. The core innovation was a radical shift in control theory, moving away from the conventional "zero error" tracking used in industrial systems toward a biologically-inspired "error maximization" principle. This approach involved maximizing positive sensory feedback (e.g., contact pressure) to achieve flexible grasping of diverse objects without explicit kinematic programming. Later iterations, including the Belgrade/USC Hand, refined this concept into "Artificial Reflex Control" (ARC), demonstrating that complex manipulation could be managed by learned, local reflex actions rather than computationally intensive, top-down instruction. Although commercially unsuccessful due to mechanical complexity and size, the Belgrade Hand is recognized as a foundational achievement in intelligent robotics.
High-Five to the Belgrade Hand: Analysis of Pioneering Robotic Prosthetics
0:02 Control Challenge: The complexity of the human hand (35 actuators, 19 internal) necessitates advanced control methods to translate simple gestures like grasping into precise prosthetic movement.
0:44 Biological Inspiration: Yugoslav scientist Rajko Tomović (Mihajlo Pupin Institute, 1960s) sought biological models to overcome the limitations of contemporary prosthetic control.
3:50 Early Control Methods: Myoelectric control (using muscle-generated electrical signals) was an established concept (pioneered in the 1910s by Sauerbruch), but pre-1960s systems were limited to crude, pre-determined action sequences.
4:45 Theoretical Foundation: Tomović posited that the mathematical theory for prosthetic control lagged behind hardware advances post-WWII, advocating for new mathematical techniques over hardware changes.
5:20 Rejection of Zero Error: Tomović rejected the standard "zero error" control paradigm (where systems minimize the difference between actual state and a fixed reference command), arguing it was unsuitable for life-like interaction.
6:11 Error Maximization: He proposed "error maximization," where the system is incentivized to maximize sensory feedback (e.g., maximizing the surface area of contact, facilitated by a conductive rubber glove).
7:33 Conceptual Leap: This control flow defined the end goal (clasping) without rigidly defining the transitional states, representing a major theoretical advance in control theory.
7:58 The First Belgrade Hand (1963/1964): This was the first recorded five-fingered robotic hand, roughly human-sized and externally powered. It was triggered by a pressure sensor in the user’s bicep.
8:52 Grasping Capabilities: Utilizing the biology-inspired feedback, the hand could perform two main grasp types: a clenching movement (resulting in a hook or a fist depending on object thickness) and a precise fingertip grasp.
9:59 Mechanical Design: The first hand was driven by a single geared motor distributing force through a complicated system of springs and levers, with finger sensors providing feedback. Its intelligent capabilities were achieved without a large, attached digital computer.
10:56 Drawbacks and Funding: Clinical evaluation identified the first hand’s mechanical complexity and large external power source as drawbacks. However, its capabilities secured funding from the US Vocational Rehabilitation Administration (VRA) in the mid-1960s.
11:47 The Second Hand (1966-1967): Developed in collaboration with the VRA, this generation improved the control logic, levers, and joints but was still deemed too heavy for practical testing (12:21).
13:42 The Belgrade/USC Hand (Late 1980s): Developed with George Bekey (USC) during an era of advanced robotics (e.g., Salisbury and Utah-MIT hands).
14:49 Artificial Reflex Control (ARC): Tomović and Bekey promoted ARC, a control philosophy based on stored, reflex-like responses triggered by learned sensory patterns, simplifying the requirements compared to complex top-down systems.
15:07 Design Improvements (Belgrade/USC Hand): The hand featured four separate motors for the non-thumb fingers and a fully articulated, two-joint thumb, designed to mount onto a robotic arm (Puma 560).
15:48 Commercial Outcome: Approximately five or six Belgrade/USC Hands were sold to research labs, but the design proved too complex and failed to gain commercial viability against simpler industrial grippers.
16:52 Legacy: Despite limited commercial success, the Belgrade Hand is celebrated as a pioneering achievement in robotics history, validating control theory based on local, biologically-inspired reflex actions.