Correcting observation errors for assembly task recognition

1 I n t r o d u c t i o n The completion of robot programs requires long development time and much effort. To shorten the programming time and to minimize the effort, we have been developing the assembly plan from observation (APO) system[I]. The goal of the APO system is enable us to design and develop a robot that can perform assembly tasks by observing how humans perform those tasks. The APO system requires precise configuration of objects for recognizing assembly tasks. Unfortunately, that obtained data usually contains errors. Those errors should be removed before utilizing the data in the system. Xiao and Zhang proposed a method to solve the contact formulation analytically in [5]. To our knowledge, they only developed a method to solve planer cases. Suehiro and Ikeuchi proposed a method to correct the errors using face contact relations[2]. Their method can handle only face-to-face relations; it cannot handle general relations, including face-to-vertex and edge-to-edge relations. We propose a method to determine precise object configurations using observed contact relations. In this paper, we also propose a method to identify wrongly determined contact relations. A correct contact relation is necessary for the method mentioned above. Although a contact relation is usually robust to vision errors, sometimes wrong contact relations are obtained. In this paper, we propose a method to identify these wrongly determined contact relations by using an analysis of the configuration space (C-space). Section 2 describes various concepts necessary to explain later sections. Section 3 describes a method to calculate the correct object configuration based on a contact relation. Section 4 develops a method to remove wrongly determined contact relations based on the C-space analysis. Section 5 explains the experimental result. Section 6 presents our conclusions. 2 P r e l i m i n a r i e s In this section, we describe various concepts necessary to introduce our proposed method. First, we describe contact relations that are indispensable for analyzing assembly tasks. Next, we describe a motion degree of freedom (DOF) that are useful for identifying wrongly determined contact relations (See in Section 4). This paper concentrates on the correct relative configuration between two objects. We consider that general n-object relations can be corrected as a series of these two-object corrections. We also assume that all objects are rigid and polyhedral. 2.1 C o n t a c t re la t ion A contact relation consists of contact-element relations. A polyhedral object is composed of vertices, edges and faces. These are contact elements. Contact-element relations are defined as those between contact elements. A contact relation can be represented as a combination of contact-element relations. Three contact-element relations are the most important ones. Contact-element relations can be classifted into nine types (Shown in Figure 1). Howface-face edge-face vertex-face face-edge edge-edge vertex-edge face-vertex edge-vertex vertex-vertex