Programmable Universal Machine for Assembly
The Programmable Universal Machine for Assembly (PUMA) is a pioneering industrial robotic arm designed for precise manipulation and assembly tasks in manufacturing environments. Developed by Victor Scheinman, a mechanical engineering student at Stanford University's Artificial Intelligence Laboratory, the foundational design emerged in 1969 as the all-electric, six-axis Stanford Arm, which emphasized articulated movement for enhanced control in automation.[1] In 1973, Scheinman founded Vicarm Inc. to commercialize the technology, and by 1977, he sold the design to Unimation Inc., which collaborated with General Motors to refine it into the PUMA series for light assembly applications targeting small parts under 1.5 kg, such as automotive components.[1][2] The PUMA arm, introduced in the late 1970s, featured a six-degree-of-freedom structure with three axes forming a spherical wrist, enabling versatile positioning and orientation for repetitive industrial operations. The first PUMA unit was installed at a General Motors facility in December 1978, marking a significant advancement over earlier hydraulic robots like the Unimate by prioritizing accuracy and adaptability for electronics and precision assembly lines.[2] Notable models included the PUMA 560, a widely adopted six-axis version for general manipulation, and the PUMA 260, optimized for lighter payloads. This design facilitated the automation of tasks previously performed manually, reducing labor in sectors like automotive production where approximately 95% of parts weighed less than 1.5 kg.[2] Beyond industrial use, the PUMA platform demonstrated versatility in medical applications, with the PUMA 200 model becoming the first robot employed in human surgery in 1985. During a neurosurgical procedure at Memorial Medical Center in Long Beach, California, it precisely positioned a biopsy needle under CT guidance, enabling stereotactic brain biopsies with submillimeter accuracy while minimizing human exposure to radiation.[3] This adaptation highlighted the robot's potential for high-precision tasks outside manufacturing, influencing subsequent developments in robotic-assisted surgery. The PUMA's legacy endures as a cornerstone of modern robotics, inspiring generations of articulated manipulators, establishing benchmarks for industrial arm designs, and underscoring the transition from heavy-duty to dexterous automation.[1][4]History and Development
Origins and Invention
The origins of the Programmable Universal Machine for Assembly (PUMA) trace back to the late 1960s at Stanford University, where mechanical engineering student Victor Scheinman designed the Stanford Arm as part of his engineer's degree thesis. Completed around 1969, this all-electric, six-axis articulated robot arm with seven degrees of freedom (including a proportional hand) represented a pioneering effort in computer-controlled manipulators, featuring orthogonal axes and brakes for precise static positioning. Unlike earlier hydraulic systems, the Stanford Arm emphasized lightweight construction and sophisticated control suitable for research applications, serving as a foundational precursor to industrial designs.[4] In 1973, Scheinman founded Vicarm Inc. in Mountain View, California, to commercialize and manufacture versions of the Stanford Arm and related designs, such as the MIT Arm developed around 1972, supplying kits to research institutions like SRI, JPL, and MIT. Facing challenges in scaling production, Scheinman sold Vicarm's designs to Unimation Inc. in 1977, joining the company as part of its West Coast division under a royalty arrangement; Unimation, originally established in 1956 by Joseph Engelberger and George DeVol for hydraulic Unimate robots, thus gained access to electric arm technology. This acquisition enabled Unimation to pivot toward more versatile, programmable systems.[4][5] The development of the first PUMA prototype in 1978 was heavily influenced by sponsorship from General Motors, which had supported Scheinman's earlier work on the Stanford Arm in the early 1970s and sought a robot for lightweight automotive assembly tasks. GM's collaboration with Unimation, initiated around 1977, focused on creating an electric, human-scale manipulator capable of handling parts under 5 pounds with high precision and reprogrammability, addressing limitations of heavy hydraulic robots like the Unimate used for spot welding and die-casting. This prototype, evolved from the Vicarm and MIT Arm designs, marked the transition to a dedicated assembly machine, prioritizing flexibility over the fixed-task rigidity of prior industrial arms.[4][2][6]Commercialization and Key Milestones
Unimation achieved its first commercial success with the PUMA robot through a partnership with General Motors, installing the initial units in December 1978 at the company's Rochester Products division for assembly tasks involving automobile subcomponents such as dash panels and lights.[7][2] This marked the transition from prototype development to industrial application, with the PUMA designed specifically to meet GM's requirements for precise, small-parts handling in high-volume production environments.[8] The 1980s saw significant expansion for Unimation's PUMA line, with thousands of units sold worldwide by the mid-decade, reflecting growing adoption in manufacturing sectors beyond automotive assembly.[9] Key corporate milestones included Unimation's acquisition by Westinghouse Electric Corporation in 1982 for $107 million, which integrated the PUMA into a larger industrial automation portfolio and shifted operations to Pittsburgh, Pennsylvania.[10] In 1988, Westinghouse sold Unimation to the Swiss firm Stäubli, enabling continued PUMA development and broader market penetration in Europe.[11] Production initially centered on U.S. facilities in Danbury, Connecticut, emphasizing domestic manufacturing to support early automotive integrations. Following the acquisitions, international licensing agreements and partnerships expanded output, including variants tailored for European markets through Stäubli's operations in Switzerland, which facilitated localized adaptations and reduced export dependencies.[9] Early commercialization faced challenges, including reliability issues in high-volume assembly lines attributed to workmanship, design flaws, and vendor-supplied components, which occasionally led to downtime exceeding expectations in demanding environments.[6] Additionally, adapting the PUMA for non-automotive sectors like electronics required modifications for finer precision and integration with vision systems, addressing limitations in handling delicate components such as circuit boards.[12]Design and Technical Features
Mechanical Structure and Kinematics
The Programmable Universal Machine for Assembly (PUMA) features an anthropomorphic design that emulates the human arm through six revolute joints, providing six degrees of freedom for precise manipulation tasks. The joint configuration includes a waist rotation at joint 1 (J1), shoulder flexion/extension at joint 2 (J2), elbow flexion/extension at joint 3 (J3), and a three-joint wrist comprising roll at joint 4 (J4), pitch at joint 5 (J5), and yaw at joint 6 (J6). This arrangement enables a spherical workspace, allowing the end-effector to reach positions within a roughly hemispherical volume centered on the wrist center point.[13][14] The base of the PUMA is mounted on a stable pedestal to provide a fixed reference frame, with each of the six joints actuated by electric DC servo motors equipped with encoders for position feedback. The arm's links are constructed from lightweight aluminum to minimize inertia while supporting payloads ranging from 2 kg to 11 kg across variants, enhancing dynamic performance and energy efficiency.[15][16][17] Forward kinematics for the PUMA are derived using the Denavit-Hartenberg (DH) convention, which parameterizes the spatial transformations between consecutive links via four parameters per joint: link length a_i, link twist \alpha_i, link offset d_i, and joint angle \theta_i. The standard DH parameters for the PUMA 560 model, widely used as a reference, are as follows:| Link i | a_i (m) | \alpha_i (rad) | d_i (m) | \theta_i (rad) |
|---|---|---|---|---|
| 1 | 0 | \pi/2 | 0 | \theta_1 |
| 2 | 0.4318 | 0 | 0 | \theta_2 |
| 3 | 0.0203 | -\pi/2 | 0.15005 | \theta_3 |
| 4 | 0 | \pi/2 | 0.4318 | \theta_4 |
| 5 | 0 | -\pi/2 | 0 | \theta_5 |
| 6 | 0 | 0 | 0 | \theta_6 |