## 1 Introduction  
Human hands are vital organs because they can help us perform the activities of daily living (ADL) every day. However, many people suffer hand dysfunction caused by accidents and diseases, especially central nervous system pathology, such as sequelae of stroke [1], traumatic brain injury [2], and spinal cord injury [3]. Hand rehabilitation training and assistance can sometimes restore their hand function to a normal level [4]. However, insufficient rehabilitation therapists and long recovery periods make it difficult to provide intense rehabilitation. To improve the efficiency of rehabilitation and relieve the workload of therapists, a series of effective hand exoskeletons have been verified and developed to offer rehabilitation training and assist ADL [5, 6, 7]. Recently soft materials have been widely used in hand exoskeletons due to their portability and good interactivity, which bring better comfort and convenience to wearers. Four main different actuation methods are widely used in compliant hand exoskeletons, including pneumatic actuation [8, 9, 10, 11], tendon-driven actuation [12, 13, 14, 15, 16, 17, 18, 19], elastomeric actuation [20, 21, 22], and hybrid-driven actuation [23, 24, 25]. In the design of pneumatic actuation, the composite [8, 9] or segmented [11] structure of the air chamber enables the hand exoskeleton to achieve a predetermined bending motion. The air chamber fitted to the finger can produce uniform force to improve comfort, which has received lots of attention. However, the hand exoskeleton with pneumatic actuation has the disadvantages of the bulky system of air pump and complex structural design of air chamber, which limits the flexibility of use in ADL. The portability and the large output force of the tendon-driven hand exoskeleton make it more suitable for ADL. For example, [PERSON] et al. [17] designed a bidirectional tendon-driven hand exoskeleton that owns a compact soft glove of 104 g and can provide a maximum grasping force of 23 N. However, the bidirectional driven tendons require elaborate capstans of different sizes to achieve the coordinated control of flexion and extension. The flexible hinges, such as sliding spring [20] or steel strap [21] are widely used in elastomeric actuation as the most necessary active driving components. The controllable deformation direction of the flexible hinge enhances the stability and safety of the hand exoskeleton. However, these hand exoskeletons need additional limiting mechanisms to assist the flexible hinge to achieve a specific bending motion. For flexible hinges used in the hand exoskeleton, there is still a lack of efficient theoretical design methods to improve the bending properties. Hybrid-driven actuation can be combined in a variety of ways. [PERSON] et al. [23] suggested a hand exoskeleton, which first flexes under the drive of tendons and then utilizes an air pump to absorb objects to grasp like an octopus. Two different active drivers improve the grasping ability, but at the same time increase the cost and complexity of the device [23; 24]. Among these considerations, a hybrid-driven hand exoskeleton with a combination of active tendon-driven actuation and passive flexible hinge has been presented [25] in our preliminary work. The active-passive hybrid-driven hand exoskeleton not only maintains the portability of the single active driver but also uses the flexible hinge to provide passive stretching force for efficient extension and a simple transmission mechanism. However, this hand exoskeleton has several shortcomings in practice:  
1. Due to the remote placement of the motor, long tendons require additional protection and guidance of Teflon tubes and reduce the efficiency of force transmission. 2. For multi-degree of freedom (DOF) fingers, each joint needs a separate flexible hinge to provide stretching force, which not only increases the number of components but also is not conducive to the wearing of hand exoskeleton. 3.