Although such a scenario is still futuristic, the development of the reconfigurable modular manipulator system, described in this paper, is a major step forward towards our goal of a rapidly deployable manipulator system。

Our approach could form the basis for the next generation of autonomous manipulators, in which the traditional notion of sensor-based autonomy is extended to configuration-based autonomy。 Indeed, although a deployed system can have all the sensory and planning information it needs, it may still not be able to accomplish its task because the task is beyond the system’s physical capabilities。 A rapidly deployable system, on the other hand, could adapt its physical capabilities based on task specifications and, with advanced sensing, control, and planning strategies, accomplish the task autonomously。

2 Design of self-contained hardware modules

In most industrial manipulators, the controller is a separate unit housing the sensor interfaces, power amplifiers, and control processors for all the joints of the manipulator。A large number of wires is necessary to connect this control unit with the sensors, actuators and brakes located in each of the joints of the manipulator。 The large number of electrical connections and the non-extensible nature of such a system layout make it infeasible for modular manipulators。 The solution we propose is to distribute the control hardware to each inpidual module of the manipulator。 These modules then become self-contained units which include sensors, an actuator, a brake, a transmission, a sensor interface, a motor amplifier, and a communication interface。 As a result, only six wires are required for power distribution and data communication。

2。1 Mechanical design

The goal of the RMMS project is to have a wide variety of hardware modules available。 So far, we have built four kinds of modules: the manipulator base, a link module, three pivot joint modules, and one rotate joint module。 The base module and the link module have no degrees-of-freedom; the joint modules have one degree-of-freedom each。 The mechanical design of the joint modules compactly fits a DC-motor, a fail-safe brake, a tachometer, a harmonic drive and a resolver。

The pivot and rotate joint modules use different outside housings to provide the right-angle or in-line configuration respectively, but are identical internally。 Each joint module includes a DC torque motor and 100:1 harmonic-drive speed reducer, and is rated at a maximum speed of 1。5rad/s and maximum torque of 270Nm。 Each module has a mass of approximately 10。7kg。 A single, compact, X-type bearing connects the two joint halves and provides the needed overturning rigidity。 A hollow motor shaft passes through all the rotary components, and provides a channel for passage of cabling with minimal flexing。

2。2 Electronic design

The custom-designed on-board electronics are also designed according to the principle of modularity。 Each RMMS module contains a motherboard which provides the basic functionality and onto which daughtercards can be stacked to add module specific functionality。

The motherboard consists of a Siemens 80C166 microcontroller, 64K of ROM, 64K of RAM, an SMC COM20020 universal local area network controller with an RS-485 driver, and an RS-232 driver。 The function of the motherboard is to establish communication with the host interface via an RS-485 bus and to perform the lowlevel control of the module, as is explained in more detail in Section 4。 The RS-232 serial bus driver allows for simple diagnostics and software prototyping。

A stacking connector permits the addition of an indefinite number of daughtercards with various functions, such as sensor interfaces, motor controllers, RAM expansion etc。 In our current implementation, only modules with actuators include a daughtercard。 This card contains a 16 bit resolver to digital converter, a 12 bit A/D converter to interface with the tachometer, and a 12 bit D/A converter to control the motor amplifier; we have used an ofthe-shelf motor amplifier (Galil Motion Control model SSA-8/80) to drive the DC-motor。 For modules with more than one degree-of-freedom, for instance a wrist module, more than one such daughtercard can be stacked onto the same motherboard。