Soft Pushing Operation with Dual Compliance Controllers Based on Estimated Torque and Visual Force

Abstract

Future robot is expected to accomplish more and more complex task, especially to work with human life. Indeed, the robot should be compliance with environment either human being. An interesting application in such an issue is pushing operation.Generally, the pushing operation consists of "approaching, touching, and pushing". However, most researches in this field are dealing with how the pushed object follows the object's trajectory. Obviously, one needs to considers the damage that may happened to the object during "touching" stage, especially if pushing operation is done by robot with high momentum.Indeed, this paper proposes a novel structure for soft pushing operation with dual compliance controllers. The robot motion will be controlled in three stages of pushing operation; approaching, touching and pushing. Although a compliance control provides robot with affinity and adaptability to work in open environment, a compliance control while touching is not enough for robot with high momentum. In which, the robot should slow down while approaching the object. Fig. 1 shows the pushing operation without any compliance behavior. Although the position response tightly followed the position command, the robot does not care whether it hit any damage on the object. The robot treats the object as an obstacle to be vanished as long it follows the position command.The compliance controller in this paper is not only for touching stage, but also for the whole stages; approaching, touching and pushing. Generally, compliance control is a control system with trajectory compensation so that an external force may be followed. The first compliance controller in this paper is driven by estimated external force based on reaction torque observer. This controller is Fig. 1. Pushing operation without any compliance behavior projected to compensate contact sensation. The second controller compensates non-contact sensation. Surely, a force sensation from force sensor either reaction torque observer is available just after the robot touched the object. It is too risky to damage the object while touching. Indeed, a visual sensor is considered as non-contact sensation. Instead of using visual information as command reference, the visual information such as depth in this paper, is treated as visual force for the second compliance controller.A heavy mobile manipulator and heavy object are considered in this paper. A chopstick is attached on the object side to show the effectiveness of the proposed method. In overall, both compliance controllers adjust the mobile manipulator command reference to provide soft pushing operation.Based on experimental results, dual compliance controllers is not enough. Although the soft pushing operation is realized, the position response could not follow the position command. Indeed, a modification on compliance controller reference is applied. The objective of this modification is to make sure the robot still follow the position command while keeping soft touching and pushing. Obviously, the soft pushing is con...

An integration method between vision-based disturbance observer and bilateral haptic system for robust tracking of target object

“…Instead of producing the position-feedback by other conventional controller [13], [14], this force-feedback type of controller is specially designed to feed into the RFOB in the bilateral control of haptic system. The construction of this controller is developed based on several parts, which are object detection, internal position controller and force generation.…”

Haptic bilateral control system with visual force compliance controller

“…Compliance control is a control system with trajectory compensation so that the external force may be followed [6]. By this control method, it is able to realize the environmental stable contact and it is possible to give system flexibility.…”

“…Thus, the combination of nonredundant position and force information to estimate compliance by a weighted summation process was proposed. Moreover, the technique of dual compliance controller also had been introduced by Muis et al that uses a trajectory estimation from produced force for automated pushing operation [6]. Nakajima et al also contribute to this bilateral control study that using the environmental information of position and posture of target object obtained by the camera [7].…”