Hyeonjun Park

Intuitive peg-in-hole assembly strategy with a compliant manipulator

To realize a peg-in-hole assembly with a multi-degree of freedom (DOF) manipulator, the precise position of the hole is required. If the hole is not circular, orientation information is also necessary. A force/torque (F/T) sensor is widely used to sense the position and orientation of the hole. Attaching the F/T sensor on the wrist of a manipulator helps in estimating the position between the peg and hole. However, a person does not need precise information of an object when completing an assembly task. For example, when inserting a plug into an outlet, a person does not need to know the exact information and coordination about the position and orientation of the plug and outlet. A closer look at the process shows that the person tries to place a plug near the outlet and then finds the two holes by rubbing the plug against the outlet without looking. This paper introduces an intuitive assembly strategy inspired by this human behavior. This strategy does not need the precise location of the hole. Instead of an F/T sensor, this strategy adopts hybrid force/position control and passive compliance control for successful peg-in-hole assembly. The feasibility of the proposed strategy was verified through simulation and a hardware experiment.

Design of an anthropomorphic dual-arm robot with biologically inspired 8-DOF arms

From the perspective of kinematics, dual-arm manipulation in robots differs from single-arm manipulation in that it requires high dexterity in a specific region of the manipulator’s workspace. This feature has motivated research on the specialized design of manipulators for dual-arm robots. These recently introduced robots often utilize a shoulder structure with a tilted angle of some magnitude. The tilted shoulder yields better kinematic performance for dual-arm manipulation, such as a wider common workspace for each arm. However, this method tends to reduce total workspace volume, which results in lower kinematic performance for single-arm tasks in the outer region of the workspace. To overcome this trade-off, the authors of this study propose a design for a dual-arm robot with a biologically inspired four degree-of-freedom shoulder mechanism. This study analyzes the kinematic performance of the proposed design and compares it with that of a conventional dual-arm robot from the perspective of workspace and single-/dual-arm manipulability. The comparative analysis revealed that the proposed structure can significantly enhance single- and dual-arm kinematic performance in comparison with conventional dual-arm structures. This superior kinematic performance was verified through experiments, which showed that the proposed method required shorter settling time and trajectory-following performance than the conventional dual-arm robot.

Dual arm peg-in-hole assembly with a programmed compliant system

In order to accomplish a peg-in-hole task with a manipulator, a cognition process is needed to extract the positional information of the objects. However, in the case of a peg-in-hole task with an extremely small clearance, or for work in an unstructured environment, the cognition process has limited accuracy, caused by factors such as resolution and disturbance. Compliance has been considered as a solution to extremely small clearance in the peg-in-hole task. In order to give a manipulator the characteristic of compliance, an RCC (remote center compliance) device is generally used. This paper proposes an alternative: Programmed variable compliance, using virtual spring controllers in task space, and verifies its effectiveness by an experiment involving fine peg-in-hole insertion with a dual arm robot.

Development of multi-purpose universal gripper

As the industrial site is changing from the mass production of a few selected items to the small quantity batch production, various works are required in the factorys production line. The single degree of freedom(DOF) gripper that can grasp only the specific object has accounted for a large part in the industrial site until now. Recently, the underactuated-method gripper that can grasp adaptively depending on the shape of object is being released, but its grip target is limitative as well. Therefore, the gripper of fully-actuated method is required to grasp and operate various objects. Therefore, the multi-purpose universal gripper that can be used diversely in various production lines is being required. The existing fully-actuated method could not be easily applied to the industrial site because it was likely to break down and it was hard to maintain it due to the complex wiring. In order to solve this problem, the multi-purpose universal gripper(MPUG) of the fully-actuated method was manufactured which was maintained easily because the modular actuator replaceable by joint link was used and which could grasp and operate various objects. It was confirmed through the test that the manufactured MPUG could grasp various objects stably.

Compliance-Based Robotic Peg-in-Hole Assembly Strategy Without Force Feedback

The peg-in-hole assembly is a representative robotic task that involves physical contact with the external environment. In this paper, in contrast to past research in the area, which has involved the utilization of such expensive devices as force/torque sensors or remote compliance mechanisms, an inexpensive method is proposed for peg-in-hole assembly without force feedback or passive compliance mechanisms. The method consists of an analysis of the state of contact between the peg and the hole as well as a strategy to overcome the inevitable positional uncertainty of the hole incurred in the recognition process. A control scheme was developed to yield compliant behavior from the robot with physical contact under the condition of hybrid position/force control. The effectiveness of the proposed method was experimentally verified using a robot manipulator with 8-degrees of freedom and a peg-in-hole apparatus with a small clearance (0.1 mm).

Optimal arrangement of base frame of a hydro-actuated dual-arm robot

This paper reports a work-in-progress result on the design of a hydro-actuated dual-arm manipulator for conducting various tasks in disaster sites. While the hydraulic actuators generally provide high load capacity, are limited in range of motion (generally smaller than 110°), thus its spatial arrangement significantly affect the kinematic performance of the manipulator. In this paper, authors particularly focus on the arrangement of base frame of each arm in order to maximize the kinematic performance with respect to overall dual-arm and single-arm tasks. Using two design parameters, (i) default yawing angle of the base joint of the manipulator and (ii) lateral distance between two arms, the arrangement of the manipulator is optimized using a workspace based performance index, PTCWA (Product of Total and Common Workspace Area).

Dual-arm robot box taping with kinesthetic teaching

Recent advances in anthropomorphic, and dual-arm robots have led to an increased interest in bimanual manipulation. One of the advantages of bimaual manipulation is the feasibility to transfer human tasks into the robot, which robots can operate in either domestic or industrial settings. Although dual-arm robot resembles human fixture, high level planning for specific task is necessary to operate the robot. In this paper, bimanual manipulation with dual-arm robot in industrial setting is introduced and application of kinesthetic teaching in box taping process is described.

Intuitive Programming of Dual-Arm Robot Tasks using Kinesthetic Teaching Method

While anthropomorphic robots are gaining interest, dual-arm robots are widely used in the industrial environment. Many methods exist in order to implement bimanual tasks by dual-arm robot. However, kinesthetic teaching is used in this paper. This paper suggests three different kinesthetic teaching methods that can implement most of the human task by the robot. The three kinesthetic teaching methods are joint level, task level, and contact level teaching. The task introduced in this paper is box packing, which is a popular and complex task in industrial environment. The task is programmed into the dual-arm robot by utilizing the suggested kinesthetic teaching method, and this paper claims that most tasks can be implemented by using the suggesting kinesthetic teaching methods.

Practical control strategy for packing multiple boxes simultaneously with dual-arm robot

This paper presents a practical and efficient control strategy for packing multiple boxes simultaneously in a congested workspace. In order to successfully complete this task, dual-arm robot has to accurately grip the boxes and insert them into a packing box while avoiding obstacles. The insertion task involves the robot accurately placing each manipulators end-effectors at contact points for multiple boxes while avoiding obstacles, firmly gripping the multiple boxes while maintaining the alignment, lifting the boxes while maintaining the gripping force, and successfully inserting them into the packing box in succession. In other words, collision avoidance, precision control, and compliance control are required in order for a dual-arm robot to pack multiple boxes in a congested workspace. Kinematic calibration is required to manipulate dual-arm robot for bi-manual operation, but this is not easy to perform and consumes a large amount of time. Therefore, this paper proposes kinesthetic teaching and compliance control for manipulating a dual-arm robot to increase the practicality and time efficiency of the multiple box packing process.

Improvement in the Control Performance of Instruments used for Minimally Invasive Surgery

Abstract: This paper presents feedforward controllers to improve the control performance of the motion and grasping force of asurgical instrument used in an MIS (Minimally Invasive Surgery) robot. The surgical instrument has a long distance between thedrive motors and its active joints. Therefore, the gripper on the instrument is controlled by a cable drive mechanism, whichgenerates a coupled motion between the wrist joint and the grip direction. In order to solve the problem, this paper analyzesthe pulley composition of the surgical instrument and proposes feedforward controllers to eliminate the coupled motion.Furthermore, feedforward controllers to regulate the grasping force are proposed to deal with another coupling problem betweenthe grasping force of the instrument and the motion of the instrument joints. The experimental results demonstrate the improvedcontrol performance of the motion and grasping force of the instrument.Keywords: MIS (Minimally Invasive Surgery), surgical instrument, tendon driven, grasping force