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This paper addresses the problem of the structure of minimum-time control of robotic manipulators along a specified geometric path subject to "hard control constraints. By using the so-called "Extended Pontryagin's Minimum Principle" (EPMF' ) and a set of parameterized robot dynamic equations, it is shown that the structure of the minimum-time control law requires that one and only one control torque is always in saturation on every finite time interval along its time-optimal trajectory, while the rest of them adjust their torques so that the path constraint on the motion is not violated. This is in contrast to the point-to-point minimum-time control law which requires that ut least one of the control torques is always in saturation. -The minimum-time control (MTC) problem for robotic manipulators can be divided into two categories in terms of different constraints on the motion: (1) The MTC problem with constrained motion paths between two endpoints; (2) The MTC problem with obstacle-free and unconstrained motion paths between two endpoints. Several solutions to the first category problem have been proposed in recent years. The second category represents a difficult and elusive problem that is not completely solved at the present time. A detailed survey of the previous research can be found in [4].Several researchers have addressed the MTC problem with constrained motion paths [l, 6-91. A technique was developed to minimize the time required to move along a prespecified path consisting of straight lines and circular arcs. In their work, piecewise constant acceleration and maximum velocity constraints were assumed [6].Singh and Leu [8] proposed a dynamic programming type algorithm for solving a general optimal control (including minimum-time control) problem along a given path with various constraints and performance indices. It was shown that the problem can be reduced to a search over the velocity of one moving link of the manipulator so that the computational efficiency is greatly improved. The motivation of using the dynamic programming approach was to develop a general algorithm capable of taking into account a variety of constraints and performance indices. The fact that the motion path is fixed enables us to discretize the given path and to determine the positions of all the other links if the position of one link is known. This eliminates the usual concern of the "curse of dimensionality" in the dynamic programming approach.In [l, 7, 91, the authors independently came to similar conclusions by following the same objective and formulation, although their numerical algorithms and motivations are slightly different. The basic idea behind their work is that a prespecified constrained motion path leads to an overall motion with one degree of freedom @OF) only, expressed by the path parameter s(t). Thus, using the parameterization along the given path, the original dynamic equations of an m-degree of freedom manipulator can be transformed into a set of m nonlinear differential equations in terms of the path par...

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A colored Pem Net model of a 'cell controller' capable of real m e control and monitoring of multiple workstations is described. The need to incorporate the ideas of both computer integrated manufacturing (CIM) and flexible manufacturing systems (FMS) is discussed and the controller is based on these concepts. The Colored Petri Net (CPN) for the cell controller is presented and described. The controller in this case controls two workstations : the Cincinnati Milacron 5VC machining center and a robotic assembly workstation using an Adept robot. An analysis of the net is performed and relevant portions are presented. A data structure for implementing this type of a CPN is given. The code for the controller is divided into application dependent and independent code. An execution algorithm is provided. The conclusions emphasize the advantages of CPNs in modelling and analysis for discrete event control of manufacturing systems.Computer integrated manufacturing (ClM) aims at improving productivity by integrating design, marketing, planning and manufacturing processes on the basis of the more recent hardware and software technologies. A simple CIM architecture, as shown in figure 1, may be viewed as a three level hierarchy: plant level, cell level and workstation level. The plant level, the topmost level, controls one or more cells, each of which in turn controls several workstations each of which are comprised of a workstation controller and several machines or devices each.Integration in c o n a~l is achieved by interconnecting the different blocks involved through an efficient information exchange mechanism.* H IFigure 1 : ducripcion of the cell level 12180-3590 &, Pi-2 : c c l l . n d~u r i o n I a y o u tRelated to CIM is the need to provide for changing market and factory conditions through flexible manufacturing systems (FMS). The degree of flexibility of a production system will not only be conditioned by the flexibility of it's elements but will depend fundamentally on the integrated control system. One of the most important goals of an FMS is to schedule resources in such a way as to meet a predefmed schedule that it receives from the manufacturing resources planner (MRP). The MRP is assumed in this work to reside at the plant level of the CIM hierarchy (see figure 1). The scheduling done by the MRP is typically at one week intervals. Therefme the MRP and the plant level scheduler have to decide on a carefully planned schedule keeping in mind the unprecedented disuptions of a factory floor. The second level in the hierarchy, the cell level, is the most interesting because it offers a wide range of problems which include scheduling (loading, routing, dispatching), monitoring, i.e., keeping track of the operations of the workstations, and reporting the cell status back to the plant. The software at this level gets complex because it has to include algorithmic aspects, real time control, database management and perhaps discrete event simulation.The workstation level has the code that directly controls the machin...

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