Force Reflecting Manipulators
EMSM/IMSM

Product Information

Telerob’s electrical Force-Reflecting-Manipulators (FRMs) were initially conceived for use in hot cell facilities in nuclear power plants, but they can be used for other purposes in nuclear and non-nuclear applications. FRMs have 6 degrees of freedom (DOF) plus the jaws motion. The units operate on the principle of the so called “master-slave-manipulators”, which is a specific term in remote handling and robotic terminology. The photographs show the 4 Telerob FRM Models: EMSM3, EMSM2B, EMSM2C & IMSM.

A. Technical Background
The manipulator has been ingeniously designed to imitate the function of a human arm. The operator moves the master arm and forces the working arm to follow accordingly. Without a complicated sensor technology, the FRM-systems offer tactile feedback that means: the operator gets feedback concerning the forces and torques, which have occurred from the working arm via the master arm. This force reflection enables the operator not only to watch but also to "feel" the work as it is performed. With this, even complicated operations can be carried out without the risk of damaging or destroying tools or adjacent objects. During operation, the weight of the items to be handled by the manipulator can be compensated by the system. The arm segments’ own weights are also compensated. The forces affecting the operator are reduced by selecting the load amplification (feedback rate) of the system and therefore minimizing the physical strain.

B. System Design
Essentially, an FRM-system consists of three components, interconnected by multi-core cables: the master (operator's) arm, the manipulator control system, and the working arm. Due to the interconnection of the components by cable, all components can be set up for mobile operation, such as attachment to a crane, excavator arm or a drive chassis. American Crane and Equipment Corp and Telerob will develop the optimum design for the customer’s specific application.

The working-arm and the master-arm are operated similarly, except for the tongs and the handle, respectively. Bilateral-positioning control with force feedback has been provided for all six or seven degrees of freedom. They are driven by electrical high performance motors. To enable force feedback, the master arm is likewise equipped with electrical motors. 

C. Manipulator Arms and Drives
All drive units of an arm are installed behind its shoulder joint. From these drive units, the power train consisting of shafts, chains, pistons or wire ropes run to the individual arm limbs. Thanks to this design, the masses to be displaced can be kept low, the arm can be made very slim, and the wrist short. The latter properties are important when operations must be performed in restricted areas, as is frequently the case.

In addition to the motor and a brake, the drive units contain temperature sensors and absolute type position transducers. Therefore, the drive units contain all components necessary to control the motions. As the components in the arms do not contain electronics (transformer based sensors etc), the manipulator provides a high radiation tolerance. The drive units are quickly interchangeable (max 4 bolts, axial dowel pins, splined shaft) making down time through maintenance as short as possible. Some remote arms are mechanically sealed while others can be equipped with a booting to avoid ingress of environmental pollution/contamination.

D. Control-unit
The electronics for controlling the entire system are located in an approximate 47” x 71” x 24” (W x H x D) control cabinet. The components are located on an assembly plate and in an electronic frame. They can also easily be assembled into customer provided cabinet space. Harnesses leaving the electronic subassemblies are equipped with connectors, so disassembly after commissioning and installation on site can be accomplished with minimal effort. In addition, the cabling is equipped with connectors wherever possible, and the entire system is supplied by one 3-phase main supply input to the control unit.

A PC-based control station, mechanically connected to the master arm stand, allows the operator to switch the system on and off and to set the machine parameters. Other functions like locking joints and operating the arms in service mode are also carried out from the control station.

The “master-slave”- control is based on the principle that a deflection of the master arm generates a new position set value for the working arm, and the force which is necessary to move the working arm to the new position, is proportionally mirrored to the corresponding master arm joint.

The control system provides force feedback, meaning that forces applied to the working arm, mainly to the gripper, are monitored. The master arm is loaded with a force, being the force on the working arm, revised by the feedback rate, and forces caused by gravity and inertia. So the operator feels only the force coming from outside to the working arm, e. g. weight of a gripped tool or feed forces to a tool. An adjustable gravity caused force can be eliminated by the system.

Additional Features
• Limitation of the working envelope: From the operator control panel, the operator can set limits to the joint angle to ensure that an arm segment stays within an allowed area. Further, full plains in the space can be defined where the arm is not allowed to pass. Those settings can be stored and called up for future use.
• Once carried out trajectories can be recorded and stored. They can be modified in speed and direction. Later they can be called up and repeated.
• Driving the working arm via 3D-joystick: The arm can be controlled via a joystick in joint mode or in the so called TCP (tool center point)-mode. Using TCP-mode is beneficial when handling tools as the system ensures that only straight lines are driven by the gripper/tool flange.