TBW.
Unfortunately, the development was shelved when Motek was acquired by a Chinese investor who also invested in Hocoma, who in turn had in their portfolio an arm exoskeleton of six times the cost and complexity, coupled to useless performance.
The torque-only idea was not the one that started the development. The original motivation was to use the skewed axes ideas from the ADL gimbal to eliminate the open circle segments, sometimes even big full ring bearings often seen near the human wrist interface, and even somemetimes even around the upper arm.
Eliminating these large bearings led to a mechanically so simple and lightweight robot arm.
, with no motors moving with the limbs, and with no cable drives or pulleys, only simple pushrods.
Several mechanical innovations were needed to make this ideal possible, as detailed below. But the major breakthrough came with the torque-only idea.
Upper arm abduction, flexion and internal-external rotation, as well as elbow flexion are powered without loading the shoulder joint and are absolutely painless. There is no setup or alignment time. Any patient can put their arm into the upper arm- and elbow brackets without any need for further adjustment.
Motors and force sensors are located in the base. The mechanism itself is very lightweight, consisting only of a few lightweight aluminium tubes. In addition, it is completely naturally balanced.
While at Moog, around 2009 I started the development of a novel arm exoskeleton. It is mechanically balanced. The mechanism gently floats when it is not powered. Bias forces ( or rather, torques ) are added to the mechanism by motors on the floor, with force sensors near the motor and admittance control to free up the motion completely.
By the use of a special elbow linkage ( modified Galloway ), ± 45° joint angles are transmitted over a series of joints with a total added angle of over 180°, all the way from the motors to the elbow and even to the wrist, by simple lightweight pushrods.
The shoulder abduction torque is driven along a horizontal axis coming from 45° back. This fits the human range of motion ( ROM ) quite closely, and since there is no translational forcing of the shoulder at all, the shoulder is free to lift and rotate around any point internal ( or even external ) to the shoulder.
This order of axes is far superior in range of motion to a vertical first axis from the world. This is often used in other exoskeletons because it provides natural gravity balancing ( or rather, indifference ) to the first axis, but this is not needed in an admittance controller, whcih only "sees" the weight suspended from the force sensor.
The video shows the final prototype in action.
There is *no* powered weight support...
The weight of the upper arm and forearm combined
is supported by a settable vertical force,
unloading the shoulder from the combined weight
of the upper arm and forearm.
This force comes (via the linkage) from the floor motor
and the single push-pull force sensor dedicated to this DOF.
The weight of the forearm,
suspended from the upper arm link,
is supported by a fully adaptive
elbow flexion torque from a second chain of pushrods
and motor plus force sensor.
Shoulder abduction is driven by a third floor motor,
rotating the red torque tube.
- skewed axes.
- abduction and eternal rotation mixed geometry.
- no vertical force on shoulder.
- torques only.
- free (unpowered) DOF's give shoulder joint 0.25 m free range in all directions.
- automatic balancing.
- additive angles via the Galloway bellcrank.
- low mass, low friction pushrods.
- all motors and force sensors at ground level.
- simple plain leadscrew drives.
- admittance control for extremely sensitive haptics.
- rubber disks take the place of small angle pivots.
- simple thrust bearings allow infinite pushrod roll.
- low cost Hudson Teknic ( ClearPath&hairps;) motors.
- one ( independent ) haptic channel per powered DOF.