Yuru Zhang

Design of an exoskeleton for index finger rehabilitation

This paper presents a new exoskeleton with 4 degrees of freedom (DOF) for index finger rehabilitation. The device can generate bi-directional movement for all joints of the finger through cable transmission, which is required for passive and active trainings. With two prismatic kinematic joints in the design, it can accommodate to some extent variety of hand sizes. The kinematic relation between the device joint angles and the corresponding finger joint angles is simple which greatly simplifies the high level motion control. As the motor capability of patients may be different and the range of motion of the finger may change along with the rehabilitation progress, it is important to take the changes into consideration. And the preliminary experiment has shown that the proposed device is capable of accommodating to these varieties.

iDental: A Haptic-Based Dental Simulator and Its Preliminary User Evaluation

Performance evaluation is indispensable for a surgical simulator to become acceptable. A haptics-based dental simulator (iDental) has been developed and preliminary user evaluation on its first-generation prototype has been carried out to gain the knowledge. Based on detailed requirement analysis of Periodontics procedures, a combined evaluation method including qualitative and quantitative analysis was designed. Construct validity was used to compare the performance difference between two groups of participants (faculty members and dental graduate students). These participants were required to perform three periodontal examination and treatment procedures including periodontal pocket probing, calculus detection, and removal. From the evaluation results, we found that penetration between tool and teeth or cheek will greatly decrease the fidelity of the simulation, therefore, it is necessary to utilize 6-DOF haptic device with both force and torque feedback in dental simulator, and accordingly it is needed to extend point-based rendering to 6-DOF haptic rendering of multiregion contacts. Furthermore, several other key research topics that will enable haptic technology to be effective in a practical dental simulator were identified, including simulation of deformable body such as tongue and gingival, and simulation of occlusion of tongue and cheek on teeth, etc.Performance evaluation is indispensable for a surgical simulator to become acceptable. A haptics-based dental simulator (iDental) has been developed and preliminary user evaluation on its first-generation prototype has been carried out to gain the knowledge. Based on detailed requirement analysis of Periodontics procedures, a combined evaluation method including qualitative and quantitative analysis was designed. Construct validity was used to compare the performance difference between two groups of participants (faculty members and dental graduate students). These participants were required to perform three periodontal examination and treatment procedures including periodontal pocket probing, calculus detection, and removal. From the evaluation results, we found that penetration between tool and teeth or cheek will greatly decrease the fidelity of the simulation, therefore, it is necessary to utilize 6-DOF haptic device with both force and torque feedback in dental simulator, and accordingly it is needed to extend point-based rendering to 6-DOF haptic rendering of multiregion contacts. Furthermore, several other key research topics that will enable haptic technology to be effective in a practical dental simulator were identified, including simulation of deformable body such as tongue and gingival, and simulation of occlusion of tongue and cheek on teeth, etc.

Configuration-Based Optimization for Six Degree-of-Freedom Haptic Rendering for Fine Manipulation

Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.

iHandRehab: An interactive hand exoskeleton for active and passive rehabilitation

This paper presents an interactive exoskeleton device for hand rehabilitation, iHandRehab, which aims to satisfy the essential requirements for both active and passive rehabilitation motions. iHandRehab is comprised of exoskeletons for the thumb and index finger. These exoskeletons are driven by distant actuation modules through a cable/sheath transmission mechanism. The exoskeleton for each finger has 4 degrees of freedom (DOF), providing independent control for all finger joints. The joint motion is accomplished by a parallelogram mechanism so that the joints of the device and their corresponding finger joints have the same angular displacement when they rotate. Thanks to this design, the joint angles can be measured by sensors real time and high level motion control is therefore made very simple without the need of complicated kinematics. The paper also discusses important issues when the device is used by different patients, including its adjustable joint range of motion (ROM) and adjustable range of phalanx length (ROPL). Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the ROPL covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device is calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. Experimental analysis shows that the influence of friction accounts for a large portion of the driving torque and warrants future investigation.

Development of a Hand Exoskeleton System for Index Finger Rehabilitation

In order to overcome the drawbacks of traditional rehabilitation method, the robot-aided rehabilitation has been widely investigated for the recent years. And the hand rehabilitation robot, as one of the hot research fields, remains many challenging issues to be investigated. This paper presents a new hand exoskeleton system with some novel characteristics. Firstly, both active and passive rehabilitative motions are realized. Secondly, the device is elaborately designed and brings advantages in many aspects. For example, joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics. The adjustable joint limit design ensures that the actual joint angles don’t exceed the joint range of motion (ROM) and thus the patient safety is guaranteed. This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient. The device can also accommodate to some extent variety of hand sizes. Thirdly, the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode. Meanwhile, the system resistance compensation is preliminary realized and the resisting force is effectively reduced. Some experiments were conducted to verify the proposed system. Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length (ROPL) covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device was calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third; for the passive control mode, the desired trajectory is realized satisfactorily.

Toward Force-Based Signature Verification: A Pen-Type Sensor and Preliminary Validation

A compact pen-type force sensor is developed to study the feasibility of force-based signature verification. A force-sensing method based on leverage effect is proposed to detect 3-D forces between the pens tip and the paper. A compact and low-cost force-sensing assembly is designed, which is integrated by five off-the-shelf 1-D force sensors. A matrix-based measurement model is established to compute the force signal in the task coordinate system (CS), which is transformed from the force signal in the sensor CS and the angle signal from a 2-D angle sensor. The structural parameters of the force sensor are determined both to achieve the required force accuracy and to meet the constraints of pen size for comfortable grasping. System performance experiments are carried out to measure the absolute and repetitive accuracy of the pen. The results show that the pen is capable for detection of 3-D force signals during real-time handwriting. Repetitive accuracy is measured to be about 0.05 N. Finally, a small-scale signature verification experiment is carried out. The verification results based on the dynamic time warping (DTW) method show that the equal error rate (EER) is about 6.3%, which illustrates the potential of the pen for force-based signature verification.

Toward Stable and Realistic Haptic Interaction for Tooth Preparation Simulation

In this paper, we present the methods to generate a stable and realistic simulator for dental surgery. First, a simplified force model is derived from grinding theory by considering the complex bur shape and dental handpiece’s dynamic behavior. While the force model can be evaluated very fast to fulfill the high update rate of haptic rendering, it also explains basic haptic sensation features in tooth preparation operation. Second, as direct rendering of this damping-like force model may induce instability of the haptic device, we apply a virtual coupling based method to guarantee the stability in haptic rendering. Furthermore, implicit integration of the bur’s motion equation is utilized to ensure numerical stability. Third, to overcome force discontinuity caused by locally removing tooth materials, we define a two-layer based representation for the bur, where the boundary voxels are adopted to compute forces and the interior voxels are employed to remove materials from teeth. The experimental results agree with the real sensation described by experienced dentists. DOI: 10.1115/1.3402759

VOXEL-BASED INTERACTIVE HAPTIC SIMULATION OF DENTAL DRILLING

Haptics is one of the most important sensations for dentists to prepare cavity in dental surgery, which is however not easy to simulate in a computer system because of the large drilling force and the small speed of movement and material removal. In this paper, we present a fully voxel-based approach to interactively simulate dental drilling. Different from those voxel/mesh hybrid models, the drilling forces are computed directly from the voxel-representation while considering the factors of teeth’s material properties, the posture and forward speed of dentist’s drill and the contact surface area. To overcome force discontinuity caused by removal of tooth material, we define two layers of voxels on drill, where the boundary voxels are only employed to compute force feedback and the interior voxels are adopted to remove materials from teeth. The experimental result shows that our force model can produce smooth and large force feedback at a slow movement on haptic devices. Other than haptic rendering, a real-time filtering method directly using voxel representation has also been developed to improve visual rendering in dental simulation.Copyright

Configuration-based optimization for six degree-of-freedom haptic rendering for fine manipulation

Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. We represent an object using a hierarchy of spheres, i.e., a sphere tree, which allows faster detection of multiple contacts/collisions among objects than polygonal mesh and facilitates contact constraint formulation. Given a moving graphic tool as the avatar of the haptic tool in the virtual environment, we compute its quasi-static motion by solving a configuration-based optimization. The constraints in the 6D configuration space of the graphic tool is obtained and updated through online mapping of the nonpenetration constraint between the spheres of the graphic tool and those of the other objects in the three-dimensional physical space, based on the result of collision detection. This problem is further modeled as a quadratic programming optimization and solved by the classic active-set methods. Our algorithm has been implemented and interfaced with a 6-DOF Phantom Premium 3.0. We demonstrate its performance in several benchmarks involving complex, multiregion contacts. The experimental results show both the high efficiency and stability of haptic rendering by our method for complex scenarios. Nonpenetration between the graphic tool and the object is maintained under frequent contact switches. Update rate of the simulation loop including optimization and constraint identification is maintained at about 1 kHz.

Haptic Simulation of Organ Deformationand Hybrid Contacts in Dental Operations

There are two main challenges in simulating bi-manual dental operations with six-degrees-of-freedom (6-DoF) haptic rendering. One is to simulate large deformation and force response of a tongue under multi-region contacts with a dental mirror, and the other is to simulate the force response when a dental probe inserts into a narrow periodontal pocket, which leads to simultaneous contacts of different types between the probe and both rigid and deformable objects (i.e., a rigid tooth and its surrounding deformable gingiva), which we call hybrid contacts, as well as frequent contact switches. In this paper, we address both challenges. We first introduce a novel method for modeling deformation based on a sphere-tree representation of deformable objects. A configuration-based constrained optimization method is utilized for determining the six-dimensional configuration of the graphic tool and the contact force/torque. This approach conducts collision detection, deformation computation, and tool configuration optimization very efficiently, avoids inter-penetration, and maintains stability of haptic display without using virtual coupling. To simulate the force response due to fine manipulation of the probe inside a narrow periodontal pocket, we propose an efficient method to simulate the local deformation of the gingiva and stable haptic feedback under frequent contact switches. Simulations on typical dental operations were carried out to validate the efficiency and stability of our approach.