Fifteen million individuals worldwide experience a stroke each year with 50,000 of these cases occurring in Canada . Approximately two-thirds of these individuals will experience neurological deficit  and half will never fully recover the hand function required to perform activities of daily living independently . Stroke survivors with severe hand impairment have difficulty producing hand motion and grip force and their increased muscle tone, spasticity and contractures keep their hand clenched in a fist. These stroke survivors have the potential to attain functional improvements years after their stroke by constantly incorporating the affected hand into activities of daily living (ADLs) and additional goal-directed tasks during their therapy exercises and daily routines [4,5,6].
There are many barriers to incorporating the affected hand into exercises and daily routines including time, discomfort, safety risks and mental and physical effort. Personalized, high-intensity, coaching and motion assistance is required to overcome these barriers but is often inaccessible to stroke survivors. The time and resource commitments are too substantial for many clinics to supply at a sufficient intensity and additional rehabilitation technologies and services can be inaccessible due to high cost, location and availability [7, 8]. As a result, stroke survivors often do not regain the hand range of motion (ROM), strength and coordination required to perform ADLs independently. Affordable and accessible rehabilitation technologies and services that enable stroke survivors with severe hand impairment to incorporate their affected hand into ADLs are needed to maximize neuromuscular recovery and daily independence.
Design targets for wearable hand robots
A main goal for wearable hand robots is to provide the hand function assistance and rehabilitation required to enable people after stroke to perform ADLs independently. Able-bodied individuals move their fingers through a ROM of 164o during activities of daily living, as calculated by summing the differences between the extension and flexion joint angles of the distal interphalangeal (DIP), proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints . The thumb moves through a ROM of 40o, as calculated by summing the differences between the extension and flexion joint angles of the thumb’s interphalangeal (IP) and MCP joints . Grip forces averaging 67 N are exerted  and a combination of hand postures are used (i.e. a tripod pinch was used during 38% of the activities of daily living evaluated, extended hand (13%), cylindrical grasp (12%), lumbrical grasp (10%), lateral pinch (9%)) .
Capabilities of wearable hand robots
Wearable hand robots have manipulated able-bodied participants’ relaxed hands to provide 129o of index finger ROM, 83 N of grip strength as measured using a hand dynamometer, and 7 hand postures in Rose et al. . However, when these robots are evaluated with impaired hands the assistive capabilities have been much lower. For studies by Cappello et al. and Soekadar et al. with six and nine persons with impaired hands following a spinal cord injury, wearable hand robots have increased grip strength to 4 N  and ADL performance to 5.5 out of 7 on the Toronto Rehabilitation Institute – Hand Function Test by assisting pinch and palmar grasp postures [12, 13]. For a study by Yurkewich et al. with five persons with severely impaired hands following stroke (no voluntary index finger extension), a previous version of the HERO Grip Glove named the HERO Glove increased ROM to 79o and improved water bottle and block grasping performance . Refer to  for a supplementary table detailing recently developed wearable hand robots, their capabilities and their evaluation results. Hand robots need to be improved to generate strong extension and grip forces that overcome muscle tone and securely stabilize various object geometries, such as a water bottle and a fork. These robots should also be easy to put on clenched hands, comfortable during multiple hours of use, lightweight so as not to affect the motion of weak arms and affordable so they are accessible to people with limited income even though these considerations create design tradeoffs that sacrifice assistive capabilities [14, 15].
A number of sensor types (i.e. button [12, 14, 16], electromyography [17, 18], motion [10, 14], force , voice , vision [21, 22] and electroencephalography  have been selected to control robot assistance based on varied motivations such as robust operation or motivating neuromuscular activation. However, other than button control, these control strategies are still in an experimental stage that requires experts to manually tune each user’s orthosis .
A single study evaluating two stroke survivors’ satisfaction with a wearable hand robot was completed by Yap et al.  to understand their needs and preferences in wearable hand robot design. More rigorous studies would further inform designers on how to adapt their wearable hand robots to maximize the intended users’ satisfaction and arm and hand use.
This article presents the portable Hand Extension Robot Orthosis (HERO) Grip Glove, including its novel design features and the evaluation of its assistive capabilities and usability with 11 stroke survivors with severe hand impairments. The HERO Grip Glove, shown in Fig. 1, assists five-finger extension, thumb abduction and tripod pinch grasping using particular cable materials and routing patterns and only two linear actuators. A fold-over wrist brace is used to mount the electronic components, support the wrist, and ease donning. The robot is controlled by hand motion or a button. The robot is open source for broad access, untethered and lightweight for unencumbered use throughout daily routines, and soft to conform to hands and objects of varying geometries. The HERO Grip Glove increases range of motion and ADL performance with large and small objects and increases grip strength for those without grip strength. The participants’ quantitative and qualitative feedback from their user satisfaction questionnaires provides guidance for assistive technology developers and motivation for deploying the HERO Grip Glove to stroke survivors for use throughout their daily routines.