Concept for Human Robot Co-operation Integrating Arificial Haptic Perception

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Concept for Human Robot Co-operationIntegrating Artificial Haptic PerceptionCatherina Burghart, Sadi Yigit, Oliver Kerpa, Dirk Osswald, and Heinz WoernInstitute of Process Control & Robotics,University of Karlsruhe,D-76128 Karlsruhe, Germany.{burghart, yigit, kerpa, osswald, woern}@a.deAbstract. Human robot co-operation becomes more and more important when usingrobots in daily life and is a key note in the design of humanoid robots. The authorsare members of the newly founded centre of excellence “Humanoid robots – co-operating and learning systems” at the University of Karlsruhe. Our group ofresearchers is responsible for the human robot co-operation, a haptic sensor systemand the control of a robot hand. All three topics closely co-operate as the humanrobot co-operation (using a robot arm and a robot hand attached to it) is mainlybased on the haptic sensor system within the first phase of the project. In this paperwe present our first classifications for human robot co-operation and contactsbetween a robot and a human or an object, which both form the basis for ourpractical work. The control concept of our robotic system is depicted as well.1. IntroductionAt the University of Karlsruhe a new centre of excellence titled “Humanoid robots – co-operating and learning systems” has been founded which focuses on the perception and the modelling of the environment of a humanoid robot (including humans) and the co-operation between human and robot. Within this scope the authors of this paper are responsible for the design and transposition of the human robot co-operation, for the design and integration of haptic sensibility and the control of a five fingered robot hand. For this purpose we use a robot arm with seven degrees of freedom and a five fingered hand attached to it as first test bed. Later, results will be transposed to a humanoid robot designed by other groups within the centre of excellence.Haptic sensors form the basis of the human robot co-operation within the first phase of the project. They are used as a means of a human user to directly and indirectly communicate his or her intentions to the robot. Additionally, the robot hand needs haptic sensors to control the grip of manipulated objects or to explore the texture of objects. The coupling of hand and arm implies the consideration of both arm and hand within different human robot co-operation schemes and a close co-operation between arm control and hand control.In the following sections we first present our classification of human robot co-operation schemes. The third section features the haptic sensor system and the fourth section describes the control system and interaction of arm, hand, human- robot co-operation module and haptic sensor system.2. Human Robot Co-operationWhen co-operating with a human the behaviour of a robot differs due to the actual task. For example, a robot holding an object manipulated by a human must have another behaviour during this task and in case of an error than a robot holding and leading a human. On the other hand, such a distinction is not always necessary. For example, a robot needs no different way of behaviour when opening a cupboard or a refrigerator. There are different kinds of tasks that need a different behaviour of the robot, whereas other tasks require the same behaviour of a robot. The first step to implementing the different, task dependent ways in robot behaviour is a classification of human robot co-operation schemes.Our classification has been created under the aspect of which situations require different behaviours of the robot. Then this classification has been used to find primitives of interpretation enabling the robot to identify each class by a specific pattern from its sensor data, internal robot data and robot environment. The classification is depicted in Figure 1.Figure 1: Classification of possibilities of Human-Robot-Cooperation.In our classification we first made a distinction whether an additional object is involved in the co-operation or not. If no object is involved there are two classes called leading and restricting. In the class leading the robot is leading the human (e.g. robotic guide dog) or the human is leading the robot (e.g. teaching). This can happen while the robot and the human have a tight connection like a grip or while they have a loose connection like a hand lying on the arm of the co-operation-partner, which results in different kinds of reactions (especially in case of an error) and opens on two new different classes. In the class restricting, the robot restricts the movements of the human (e.g. separating the human from dangerous areas) or the human restricts the movements of the robot (e.g. stopping the robot as a additional concept of safety). This can either be done while the robot and the human are touching each other in a tight grip or - within the class room guardian - while one partner of the co-operation is prohibiting the other form entering an area by crossing his trajectory with parts of his own body in case the other would enter the area. In all classes there is no object directly involved in the co-operation, but this does not mean that there isno object involved at all i.e. a robot can carry an object while it is lead by a human to another place.If there is an object directly involved in the co-operation there are two possible schemes of interaction between human and robot. Either they are just handing over the object or they both manipulate the object at the same time.In case of handing over there is the possibility of a direct handover, which means form hand(s) to hand(s), or the possibility to transfer the object by using a medium. The direct handover requires different ways of behaviour if the object is presented in a fixed configuration that has to be opened during the handover (i.e. a closed hand), or if the object is presented in a way that the other partner of the co-operation can just take the object. These classes can be classified into smaller and more specific classes by focusing of the kind of grip(s) used to hold the object. The handing over of an object by using a medium can be achieved by placing it somewhere in the working space of the partner of the interaction or by throwing (or dropping) it into the partner’s hand.In case of the object manipulation, there are three different classes according to the movement and forces of the participants of the co-operation in aspect to each other. Those can be symmetric, anti-symmetric or independent. In the symmetric case, the movement of the robot and the movement of the human are the same to reach the aim of the co-operative task, like carrying, pushing or pulling something together. In the class anti-symmetric object manipulation the movement of robot and human and the forces generated by them are working against each other. Examples for anti-symmetric object manipulations are things like opening a screw plug or tearing off a piece of paper. If the robot and the human are doing different manipulations on the same object or work on different objects that have a connection to each other, this kind of interaction is found in the class independent object manipulation i.e. filling a glass held by the robot or taking something from a plate carried by the robot.All of the classes have the potential to be split into further subclasses; we already have eleven different classes, most of them resulting in different ways of behaviour of the participants; the behaviour depends on the part of the task done by the robot and by the human, which all in all results in about twenty-two different interactions schemes.The classification of co-operation schemes is basis of the specification of so called interpretation primitives. These primitives combine data and patterns of sensors, the robot, the environment and the human in order to specify and interpret the different steps of a specific co-operation between human and robot. Some of these data are gained by artificial haptic perception.3. Artificial haptic perception: pre-classification of mechanical contactsThe model of the artificial haptic perception is the human sense of touch. It is often considered to consist only of the tactile sense of the skin which is only a part of it. The bathyaesthesia or deep sensibility is also an integral part of this human sense. It includes the senses of force, position and movement of the different parts of the human body [1]. These haptic information –tactile ones and forces- in combination with information about the context of the robot and its environment allow a classification of a detected contact with the environment (Fig. 2 and Fig. 3).In the case of human robot co-operation the class of control contacts is relevant. A contact identified as a control / positioning contact can initialise a co-operation task but the robot needs further information which task is demanded. These information have to be given by other senses e.g. the auditory sense; limiting to haptic perception it would beimaginable to give commands directly using the tactile sense as an input interface which matches defined input patterns with defined commands.In the following classifications a sensor system comprising surface and depth sensibility of a robot is considered. Surface sensibility is achieved by using tactile sensors in foil design applied to the robot arm and hand with different spatial resolution. The palm of the robot hand and the finger tips are supplied with sensors at relevant point to support hand control. Depth sensibility is realised by acceleration sensors and a force torque sensor in the wrist.3.1 Classification of contactsThe main purpose is the classification of contacts according to the quality of intention.We are proposing three classes of contacts which cover all possibilities of interaction between a robot and its environment: collisions , control contacts and task contacts . These main classes can be split in generic sub-classes which can be partly divided again in specific contact patterns e.g. the sub-class grip can be divided in a taxonomy proposed by Cutkosky and Wright [2] with related contact patterns. In Fig. 2 the classes and sub-classes of contacts are shown and will be explained in the following.Collisions can be described as contacts that are not intended at all, neither from the robot nor from its environment. The differentiation of this class in collisions of the robot with humans or objects is making sense if there are different reactions of the robot in such cases.Control contacts are initiated by the robot’s environment with the purpose to give information or commands to the robot. The sub-class positioning is quite near to the model of intuitive human-like interaction because it does not require further information but contacts and forces. Using the tactile sensing as an input interface for defined commands via contact patterns –contacts called command inputs - is not quite that kind of human-like interaction but there are imaginable situations in which it would make sense e.g. in loud environments or simply when the robot does not have other senses.Task contacts are contacts that are related with the actual task of the robot and therefore they are expected and mainly initiated by the robot. In the case of grips these are specific contact patterns for each particular grip. Exploration contacts are initiated by the robot and expected in a certain area of its body e.g. a fingertip but a further differentiation by means of properties to be explored is necessary e.g. the shape of an object.Support describes contacts which are expected as part of a support task e.g. the robot supporting a person with its arm.Figure 2: Contact classes and sub-classes3.2 Parameters of the formal descriptionTo perform a classification a formal description of these contact classes is needed. The parameters on which this description is based include information about the context of the robot-human mechanical contact with environmentcollision task contactcontrol contact grip positioning exploration supportcommand input robot-objectrobot and its environment and, naturally, characteristics of the sensor signals. As seen above in the description of the contact classes appears the quality of intention or expectation so we have chosen the following four parameters concerning the context:Operation mode of the robot: the robot has a task to perform or not (it is active or passive ). When the robot is passive it is in a stand-by-mode and is waiting for an input (“lurking mode”). When it is active it has a task to perform with a related contact pattern (“no contact” represents also a contact pattern e.g. for the task “go from point A to point B”).Expectation of the robot: the perceived contact is expected or not expected. When the robot is active a contact is expected if it is matching the related contact pattern; if not it is unexpected . When the robot is passive all contacts are unexpected . To perform this differentiation the actual contact pattern has to be given to the contact classification unit.Status of the environment: whether there are autonomously moving objects (humans or other robots) in the workspace of the robot (dynamical ) or not (static ). If this information is not available, the default status of the environment has to be dynamical for safety reasons.Intention of environment : a contact can be intended or unintended by the environment.The combination of these four parameters with two possibilities each results in sixteen sets of parameters. Half of these sets do not make sense e.g. a passive robot does not expect any contacts, therefore any contact is unexpected; and to provoke any contact the environment has to be dynamical . In the following diagram (Fig.3) the reasonable combinations with their derived contact classes are shown.Figure 3: Parameter sets of contact classesAs it can be seen, the three contact classes can be distinguished on the basis of these four parameters. The sub-contact classification has to be performed on the basis of the characteristics of the sensor signals.In the case of task contacts the related pattern must be given to the classification unit.A possibility to differentiate collisions of the robot with a human or an object could be the acceleration measured in defined points on the robot. This integration of acceleration sensors in the haptic perception system will be investigated. In the field of robotic control this approach already has been tested [3].In the class control contacts two sub-classes have to be differentiated. The contact patterns for direct input of commands are defined (e.g. in a kind of morse code) but mechanical contact with environmentrobot passive robot activeenvironmentunintended environment intended robot unexpected robot expectedenvironment static environment dynamicalenvironment static environment dynamical environment unintended environment intended environment unintended environment intended collision collision collision task contact control contact control contact task contacttask contact robot unexpected environmentdynamical environment unintended environment unintendedsomehow the input has to be initiated. Using only a part of the robot body as input interface e.g. the back of the hand in combination with an initiation pattern like “three taps” would be a possibility. To recognize a positioning contact the tactile pattern can be used. To lead a robot the user has to grip a part of the robot e.g. the arm. This grip results in a tactile pattern that has opposing areas which would be one possibility to recognize the initiation of a positioning task.Furthermore the classes collision and control contact must be differentiated if environment information is not given. Measurement of accelerations, forces in the joints and the analysis of tactile patterns - whether they are probable for a collision or not - will be investigated.4. Control SystemThe control system of the robot must be specially designed to be able to fulfill the desired tasks. For cooperative tasks the physical interaction between a human and the robot is a key issue. Because robots are usually much stronger and mechanically more robust than a human being, this physical interaction is potentially dangerous for the human. Therefore the control system has to guarantee the safety of the human at all costs.Generally a control system has to perform the three steps 'perceive', 'process' and 'act' to fulfill tasks like object manipulations or movements. But not only a robot performs these steps, but also a human being. While the robot uses its sensors to 'perceive' the human uses his or her senses. The 'processing' is done by software on a microprocessor for the robot while the human uses the central nerve system. And finally the robot 'acts' using actuators like motors and the human uses his or her muscles. For the human-robot-cooperation with physical interaction the acting of the robot is perceived by the human and the acting of the human is perceived by the robot. Therefore the human closes the control loop from acting to perceiving for the robot and vice versa [4].Figure 4 shows the proposed control system for the robot used for the human-robot-cooperation schematically. The approach is based on the 'classical' hierarchical control architecture [5], [6]. The figure also shows the human involved in the cooperation as described in the previous paragraph. At the highest level shown in the figure is the human-robot-cooperation module. This module decides what to do, i.e. how to 'act', according to:•the classification of possibilities of human-robot-cooperation described in section 2•the interpreted sensor data, like e.g. the classification of mechanical contacts described in section 3•context information about the environment from the internal model.The 'acting' commands from the human-robot-cooperation module are then forwarded to the high and low level control of the different actuators. The complete robot planned in this project will consist of a 'body', i.e. a mobile platform, equipped with two arms, two hands and a head. The respective sub-control systems for these sub-systems are not considered here, because their specifics are not relevant for the human-robot-cooperation (see e.g. [7]). For the first phase of the project a simpler mechanical system will be used, consisting of one fixed robot-arm equipped with a humanoid hand with up to 5 independent fingers.The sub-control systems of body, arm and hand control the different actuators of the robot respectively. These mechanical actuators, like motors, pneumatic cylinders etc., physically interact with the human cooperation partner. This interaction can be more or less mechanically direct, as discussed in section 2.The human perceives the acting of the robot with his or her senses, processes the perception and reacts by actuating his or her muscles. This reaction is in turn perceived by the robot with its sensors. To perform the physical interaction safely for the human allrelevant physical sizes must be sensed. Therefore not only the usual position sensors are needed but many additional kinds of sensors, like e.g. tactile, force, torque or acceleration sensors.The raw sensor data must be preprocessed and prepared for further evaluation. This sensor data is then used as feedback signal for the control systems of the body, arms or hands. Additionally the data can be stored in the internal context model of the environment. The preprocessed data is also used to classify the mechanical contacts as discussed in section 3. This step hence interprets the information contained in the sensor data in order to perceive 'what is going on' in the environment. This information can as well be stored in the internal context model of the environment, but is mainly used by the human-robot-cooperation module. This closes the overall control loop.Figure 4: control system for cooperation between robot and human5. ConclusionHuman robot co-operation involves the robot’s perception and interpretation of human actions. For this purpose we have set up a classification of possible human robot co-operation schemes as a basis to design interpretation primitives for robot control; which considers co-operation with or without an object, leading a partner or restricting the movements of a co-operation partner, and the different manners of manipulating the same object at the same time.Closely related to the classification of the human robot co-operation schemes is the classification of the robot’s contacts with its environment, especially considering the intention of the environment and the robot’s expectation of commands according to patterns defined by the interpretation primitives of the human robot co-operation unit. Here,haptic sensors are one of the basic sensor systems to pass the appropriate information and a pre-classification on to the human robot co-operation unit.The present test bed for our research comprises a robot arm and a humanoid hand attached to it as well as different tactile sensors for surface sensibility and haptic sensors for depth sensibility. In our paper we have also presented the concept of the control system involving robot arm, robot hand, human, and the robot’s artificial haptic sensor system.Future work comprises the definition of interpretation primitives for human robot co-operation and the planning and transposition of co-operative tasks. Different sensors are tested and integrated and sensor patterns as well as contact patterns have to be specified. In a later phase of the project further sensors are to be included in the human robot co-operation. All newly designed methods will be tested with our testbed. AcknowledgementThis research was performed at the Institute of Process Control and Robotics, headed by Prof. Dr.-Ing. H. Wörn, at the University of Karlsruhe. The work is being funded by the German Research Foundation, as it is part of the special research program “Humanoid Robots – Learning and Co-operating Systems“. References1Schmidt R.F., Thews G.: ”Physiologie des Menschen”, 27.Aufl., Springer, 1997.2Cutkosky M.R., Wright P.K.: ”Modeling Manufacturing Grips and Correlations with the Design of Robotic Hands”, Proc. IEEE Int. Conf. Robotics and Automation, pp. 1533-1539, 1986.3Stelter J.: “Verbesserung des Positionierverhaltens und der Bahntreue eines Industrieroboters durch den Einsatz von Beschleunigungssensoren”, Shaker Verlag, 2001.4Geiser, G. (1990): Mensch- Maschine-Kommunikation. Oldenbourg Verlag, 1990.5 B. 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