Planar motion systems based on commercial Sawyer motors provide uniform performance over their entire workspace, offering fairly high speeds (1.5 m/sec), accelerations (30 m/sec/sup 2/), and precision (sub-micron resolution). Using multiple motors over a common plateau provides an excellent basis for an agile table top, very high resolution, manufacturing system. Sawyer motors have 3 planar degrees-of-freedom X-Y-Yaw (rotation in the plane). The motor is very sensitive to yaw rotation, its force decreases rapidly, and it can lose synchronisation. This paper develops an analytical model of the motor, provides guidelines for the design and a real-time compensation method for errors resulting from yaw rotation. The model applies to magnetic, capacitive and optical position sensing using the platen as a reference grid.

A critical component of throughput for planar assembly and test systems is time spent moving from site to site. In general, it is difficult to assess the impact of actuator improvements on overall system performance. It may vary from product to product. Even for a specific product, it may depend on which of n factorial possibilities is chosen in moving amongst n locations. Ideally, one wants to minimize the total time required by all the movements. Since the improvement affects the time required to move from site to site, the optimal sequence may also change. It was shown that with proper single parameter actuator-scaling, the optimal sequence remains unaffected. Furthermore, the improvement in the system's performance is quantifiable, independent of the distribution of the distances that must be traversed. In a case that a proper single parameter actuator-scaling does not exist, it is shown here that bounds on system performance can still be obtained, even though the optimal sequence may change. The bounds are independent of the distribution of the distances that must be traversed.

Planar motion systems based on commercial Sawyer motors (1969, 1973, 1974) provide uniform performance over their entire workspace, offering fairly high speeds, accelerations, and precision. They also offer mechanical and kinematic simplicity, modularity, large motion ranges, and a short path to mechanical ground. On the other hand, primarily because they are operated as open-loop step motors, they can miss steps, have long settling times, and fall short of their potential capabilities. These motor performances are improved by using a novel, very high resolution (0.4 /spl mu/m), Sawyer planar sensor presented in this paper.>

A planar step Sawyer-motor system consists of a Sawyer-motor riding on an air-bearing over a thin steel platen. The platen has a fine grid of teeth which the motor uses to move on the platen. Due to the heat generated from the motor, the platen along with the grid deforms such that the actual position of a point on the platen is equal to the nominal position of the point plus some thermal deformation. Thus, the maximum accuracy is limited to the maximum error from the thermal deformation, which was about 60 /spl mu/m over a range of 0.5m, in our test system. This paper presents a finite element model for real-time prediction of the thermal deformation of the platen of a planar step motor, along with experimental verification of the model. The model can be used to compensate for the thermal deformation, thus improving the positional accuracy of the motor. The results show that an improvement in positional accuracy of about a factor of five can be achieved.>

It is demonstrated experimentally that a variable-reluctance linear step motor can be controlled as a programmable spring with a spring constant of dynamic range 2000 to 1 for robot applications. This large dynamic range is mainly attributed to the direct-drive use of this variable-reluctance linear step motor. Using direct drive provides a high ratio of output force to friction because of the lack of commutation brushes and a reduction gear. The large dynamic range of achievable spring constants also demonstrates that a very simple electronic commutation-logic feedback can simplify a statically and dynamically complex variable-reluctance step motor to the point that it can be algebraically linearized. For a large operating range in force, velocity, and frequency, this linearized model can be approximated by a second-order ordinary differential equation; i.e. the force on a mass given by Newton's second law with the addition of a small friction force.>

A description is given of the software environment for SPARTA (signal processor architecture for real-time applications). The SPARTA hardware consists of a hybrid system with three different types of computers. The program development environment includes the PLH high-level language (on an IBM VM/CMS mainframe) for generating efficient real-time signal processor code. The runtime (user) interface (on an IBM PC) supports symbolic debugging, dynamic loading and linking, and synchronous switching of control algorithms during real-time program execution. It has been interfaced to the object-oriented AML/2 language interpreter. The real-time environment (on multiple IBM Hermes signal processors) has tasks with multiple entries and exits, linked by a method which is somewhat similar to threaded code, but which has lower overhead (0.1 mu s, nonpreemptive task switch). The real-time kernel also supports multiple threads of tasks categorized as critical or abortable, reflecting their importance to the real-time system. These threads are scheduled by a priority-based, preemptive scheduler, which has 1.3-5.1 mu s total overhead. A SPARTA system with one Hermes signal processor, executing a dozen real-time tasks, has achieved a sample rate of 5 kHz for a fully-coupled PID control, with nonlinear compensation, for the Eaglet II Cartesian robot (five motors achieving 2- mu m linear resolution and 0.02 degrees angular resolution).>

The authors describe the SPARTA (signal processor architecture for real-time applications) system, which is a hybrid computer development system including: (1) a program development environment on an IBM VM/CMS mainframe computer: (2) user interface and runtime support on an IBM PC; and (3) real-time computation and input/output using multiple IBM Hermes signal processors situated on the IBM PC bus. The program development environment includes the PLH high-level language for generating efficient real-time Hermes code. The runtime supports symbolic debugging, dynamic loading and linking, and synchronous switching of control algorithms during real-time program execution. The real-time environment includes a distributed operating system which supports foreground and background task execution and real-time data collection and display. The task switching overhead is 0.1 mu s, nonpreemptive, and 1.0-3.7 mu s when the context is changed by an interrupt (i.e. preemptive).>

The SPARTA (signal processor for advanced robot technology applications) system is a hybrid computer which includes: (1) program development environment on an IBM VM/CMS mainframe computer; (2) user interface and runtime support on an IBM PC; and (3) real-time computation and I/O using multiple IBM Hermes signal processors situated on the IBM PC bus. The program-development environment includes the PLH high-level language for generating efficient real-time Hermes code. The runtime supports symbolic debugging, dynamic loading, and synchronous switching of control algorithms during real-time program execution. The real-time environment includes an operating system which supports foreground and background task execution and real-time data collection and display. A SPARTA system with three Hermes signal processors is currently being used to develop control algorithms for a two-axis fast direct-drive Cartesian robot at sample rates in excess of 10 kHz;.>

Traditionally the translation of a given task into robot actuator commands involves three translation steps: (i) Task level planning; given the task find the manipulated object's required motion. (ii) Robot motion planning; given the manipulated object's required motion find the desired robot arm trajectory. (iii) Robot controller; given the desired robot arm trajectory find the robot actuator commands. Furthermore, the robot controller is fixed and internal and is typically not modified in accordance with the expected interaction between the robot arm and the objects it is manipulating. Thus the fixed robot controller is a major handicap which limits the possible robot interactions and performance during such interactions. In this paper we suggest that the objectives of the robot controller be "elevated" from attaining robot arm level objectives to attaining task level objectives. Consistent with this view, the following new three step Funnel algorithm is suggested for the translation of a given task into robot actuator commands: (i) Partition the task into a sequence of local sub-tasks and local regions. (ii) Synthesize a feedback control law to achieve each sub-task locally. (iii) Apply the local feedback control law to obtain the required actuator commands. It is expected that using this funnel approach both the robot system performance and functionality can be improved.

An abstract simulator design problem is formulated as follows: we are given a dynamic system Sa called the actual system and another dynamic system SS called a simulator for Sa. Furthermore, we are given an input signal which drives the actual system Sa. The problem is to find an operator, properly constrained, which generates the input to the simulator Ss on the basis of the input to Sa so that the discrepancy between the output of Sa and Ss is as small as possible. This abstract simulator design problem is brought to the form of an optimal control problem and then solved for the linear-quadratic-Gaussian special case. Next the soluiion of the abstract simulator problem is applied to the design of motion generators for flight simulators. A fairly elaborate mathematical model of the vestibular organs is used. The optimization criterion that is selected is the mean-square difference between the physiological outputs of the vestibular organs for the pilot in the airplane and for the pilot in the simulator. The dynamical equations are linearized, and the input signal is modeled as a random process with a rational power spectral density. Subject to the above assumptions, the optimal structure of the motion generator for the simulator, also called a "washout filter," is derived. This method stands in contrast to existing design schemes for motion generators which generally assume a certain fixed structure for the motion generator and concentrate on optimizing its parameters.