TELESAR I

Susumu Tachi (born 1946) studied mathematical engineering and information physics at the University of Tokyo. After hearing a radio broadcast of Norbert Wiener's The Human Use of Human Beings in 1965, he devoted himself to cybernetics research. From 1975 he worked at the Mechanical Engineering Laboratory (MEL) in Tsukuba Science City, under Japan's Ministry of International Trade and Industry (MITI). He spent 1979–1980 as a visiting scientist at MIT. On the morning of September 19, 1980, walking down a laboratory hallway at MEL shortly after returning from MIT, he had an epiphany: if technology could continuously present a remote person with the identical retinal images they would receive from direct vision, they could essentially 'exist' across space and time. He filed two foundational Japanese patents: 'Evaluation Device for Mobility Aids for the Blind' (filed Dec 26, 1980, patent 1462696) and 'Operation Method of Manipulators with Sensory Information Display Functions' (filed Jan 14, 1981, patent 1458263). The first English-language paper appeared in 1984 at the RoManSy symposium.

The master system consisted of a head-coupled stereo display (two 6-inch monochrome LCDs at 720×240 pixels with convex lenses and mirrors), a 10-DOF master arm, and a counterbalanced 6-DOF link mechanism for head tracking. The slave robot was anthropomorphic: 60 kg, 7-DOF right arm with a 6-axis wrist force sensor, 3-DOF neck carrying two color CCD cameras (420,000 pixels each, f=12mm, 40° field of view) and two binaural microphones spaced 243mm apart (matching the master display's ear spacing), a 1-DOF waist twist, and a gripper hand (1-DOF pinch/grasp) weighing 620 g with a DC motor, ball screw, parallel-link mechanism, and strain gauge force sensing. Locomotion was provided by a planar polar-coordinate mechanism (500–1500mm radial, 270° angular). Four Intel 286/386 computers ran MS-DOS with C-language control programs totaling 11572 + 76983 + 22611 + 86375 bytes. The control cycle was 10 ms.

The operator sees the remote environment through the robot's eyes; when the operator turns their head, the robot's neck turns correspondingly, changing the camera view in real time. When the operator's hand moves, the robot's arm moves identically. Crucially, the slave arm appears in the operator's HMD at the exact spatial position where the operator's proprioception expects their own arm to be — creating a seamless sensorimotor loop. Tachi called this a 'virtual exoskeleton' — the operator is not wearing the robot body physically (as in GE's Hardiman, 1967) but experiences the same embodiment effect without the physical danger. This was a conceptual Aufhebung (sublation) of two contradictory paradigms: the dangerous physical exoskeleton and the disembodied autonomous supervised robot.

The term 'telexistence' was Tachi's independent coinage (1980), nearly simultaneous with Marvin Minsky's 'telepresence' (OMNI magazine, June 1980). The concepts differ in three ways: (1) telepresence does not include virtual environments — telexistence explicitly includes both real remote environments AND computer-generated virtual environments; (2) telepresence is an extension of teleoperation, while telexistence is a dialectical synthesis of exoskeleton and autonomous robot paradigms; (3) telexistence robots (avatars) are intelligent autonomous robots that can also be human-controlled, while telepresence robots are slave devices with no autonomy. Tachi founded the first international VR conference (ICAT, 1991), the Virtual Reality Society of Japan (1996), and later Telexistence Inc. (2017), which deployed avatar robots in Lawson convenience stores in 2020.

Tachi conducted rigorous human-factors experiments in 1989–1990 comparing five display conditions: (1) direct observation (control), (2) binocular HMD with head tracking, (3) monocular HMD with head tracking, (4) fixed CRT at 45° FOV, and (5) offset CRT at 30°. Operators performed a pursuit tracking task following a pseudorandomly moving target with the slave manipulator. Results showed clear superiority of the binocular head-tracked HMD over all CRT conditions, with significantly higher crossover frequency (fc) and lower effective time delay (Te). The binocular HMD approached direct-observation performance. The results were published in Presence journal (1994) and established the quantitative basis for head-coupled stereo displays in teleoperation.

TELESAR I proved the core hypothesis: tight visuomotor coupling between human and machine creates genuine presence. The TELESAR series continued through TELESAR VI (2020, 67-DOF full-body avatar with 10-finger haptic feedback including force, vibration, and temperature). Tachi's 30-year-cycle conjecture predicts a major societal shift toward telexistence in the 2050s. The Japanese government's Moonshot R&D program (2020, ¥115 billion) made 'cybernetic avatar society' its first of six goals — directly tracing to Tachi's work.