Sensors and Transducers Grant Agreement No LLP UK-LEONARDO-LMP Project acronym: CLEM Project title: Cloud services for E-Learning in Mechatronics Technology

Sensors and Transducers Control of mechatronic device based on two types of sensors – f/t sensors and position sensors Algorithms for controlling the working mechanisms under modeling the resistances at the joints Two possibilities are analysed: creation of the resistance using a direct-current motor with built-in reduction gear (MR) and with an electromagnet brake. Resistance modeling at the joint using MR. A reduction gear with a two-directional transmission of the movement will be used. The torque Tx would be measured and the angle (θ) of rotation around the same axis. Initial position – robots grasp the orthosis at the initial position and start the movement into the direction + (positive). A functional converter is included at the control of the MR to be possible the creation of the resistance into two-directions of rotations at the joint and the change of the specifying torque depending on the value of the angle (θ). Two functions would be realized: Tdefined =sign∆θ.T or Tdefined =sign∆θ.f(  )

Sensors and Transducers Principle of action The direction of movement at the beginning of the cycle is + (positive), which defines a positive value of the specifying torque at the beginning of the movement. The MR should be rotated in – (minus) direction in order to be created that value at the joint because the resistance of the reduction gear will be not able to create the needed resistant torques. The MR will reversing when will be reached the value Tspec=Tθ and as a result from the inertia of the system ∆T will be minus value. The value Tθ is reducing under the new direction of movement (+). The MR changes its direction of rotating at ∆T=0. A varitype regime will appear around the specified value Tspec. It is expediently to be implemented a short area of insensibility (±ε) or to be used a regulator with a more complex law of regulating in order to be reduced the variations during the movement. The described algorithm allows a zero resistance to be imitated at the joint and the MR should to overcome the resistance of the reduction gear. The direction of movement should be defined according the sign of increasing (∆θ) of the coordinate. It is expediently to be formulated a threshold of distinction δθ to be reduced the influence of the interferences over the working algorithm (including the vibrations) while defining the sign of ∆θ. ∆θ saves its sign from the previous step if |∆θ|≤0, while |∆θ|>δ∆ then Dsign= sign∆θ. Tspec changes its sign during the change of the direction of the movement. The described algorithm gives a possibility to be imitated active movements for overcoming the external force acting, not exceeding the value of Tspec. The sign of Tspec should be changed at the control system in this case.

Sensors and Transducers A reduction gear with a one-directional transmission of the movement will be used The reduction gear instead of the motor at that case creates the resistant torque, which means that when is defined the direction of movement (defined from the sign of ∆θ) the motor has to be rotated at the same direction when Tθ>Tspec. There are two possible states of the motor during the movement at the defined direction – rotating in the same direction and motor shut off. The value of Tspec and the direction of the movement are defined as the previous case. Some mistakes can occur, for example wrong defining the direction of movement and to be limited such regrettable effects there is a necessity to be applied a possibility to be stopped the procedure under exceeding Tθ over defined threshold value Tθthr. The procedure should be stopped when |Tθthr|≥ Tθthr or a component from the force acting over the orthosis exceeds the specified threshold value. Resistance modeling at the joint using a servo brake The value of Tspec is always positive at this case and is defined using the dependences: Tspec=T or Tspec= + f(θ)

The brake catches (Vbr=0) at |Tθ| ≤ Tspec and releases at |Tθ| > Tspec (Vbr=Vsupl). The modeling of zero resistance at the joint is not possible at this case. The resistant torque will be defined from the friction forces at the bearing unit at the joint and the brake while the brake is released. The brake will be always released at Tspec=0 Sensors and Transducers Algorithm for defining the direction of movement and the sign of T defined

Sensors and Transducers Control system The main task of the control system is the support of resistance torques in the artificial arm’s joints. The control system is developed on three levels hieratical principle. The lowest level is developed from the electric actuators of the different controllable axis. A DC motor, controlled by a specific controller – DC Motor Controller, Fig.11, performs the motion on each axis. Exception makes two of the controlled axis in which the DC motors are replaced by electromagnetic brakes. The resistance torque of the brakes is controlled by PWM (Pulse Width Modulation) signal. Second level in the hierarchical control system is the control unit that calculates the current resistance torque on each axis and sends control signal to the DC motors’ controllers. For calculation of the control signals to the electromechanical brakes is used a specialized calculation block Torque/PWM Converter.

Sensors and Transducers On the top of the hierarchical control system is the “Programmed model of the arm”, calculating the required resistance torque for each one of the controlled axis dependent from the “condition of the arm” and the rehabilitation procedure. The “Programmed model of the arm” works in a personal computer (PC) external of first and second control levels. As a result of the work of the programmed model are calculated the tasks (set points) of the resistance torque of each one of the controlled axis: T i =f(  i ); i=0  7,where T i is the defined torque for axis number ‘i’;  I is the current joint angle Second task of the control system is the recording of information (database) for the execution of a rehabilitation procedure. Information for the real resistance torques of the controlled axis is sent from the control unit (second hierarchical level) to the PC in order of oriented couples of digits: R ij =(T ij ;  ij ); i=0  7, j=1  N,where R ij is record number j for axis number i;  ij is the measured angle of the controlled axis with number i at moment j; T ij is the calculated resistance torque of axis with number i, corresponding to the measured angle  ij.

Sensors and Transducers System for formulation of controllable muscle reactions (BTF- block for task formulation; EA – electronic amplifier; MG – DC motor coupled with gearbox; SA –angle sensor; F/T force/torque sensor; TB – transformation block; R – regulator)

Sensors and Transducers Control algorithm

Sensors and Transducers Local network

Sensors and Transducers The program for control of the artificial arm is realized on second hierarchical level, while the lowest level is hardware. The controls of each of the axis include block for calculation of the control action (control algorithm) and block for definition of the current value of the resistance torque (calculation block). The block for calculation of the control action includes calculation procedure based on standard PID algorithm. It may be assumed that the procedure is one and the same for all electric actuators instead of the specifics of each axis. The block for definition of the current value of the resistance torque is different for each one of the axes. The complexity of the calculation procedure is defined mainly from the position of the controlled axis according the position of the F/T sensors, respectively the geometry of the dummy limb. The quality of the control depends from the speed with which the control unit performs the calculation procedures and sends control signals to the actuators. One of the possibilities to increase the processing speed is to distribute the tasks on certain number of controllers working simultaneously. This method is known as “distributed control system”. The information exchange between the different controllers and their synchronization is organized through a local network.

Sensors and Transducers In the control system of the dummy limb the task for control of the different axis is distributed between four PLCs. Each PLC controls a couple of axis. The synchronization between the different tasks is organized with local network SIMATEIC S7 200 PPI Network specific for the chosen type of PLC. The communication speed in the local network is restricted to 9600bps and the use of this speed for connection between second and third level will reduce the synchronization accuracy of the tasks between the different PLC on the second level. For this reason the information between second and third control level is performed by a high-speed network PROFIBUS 12,5Mbps. The personal computer is the master of the PROFIBUS network while the slave modules ensure the direct access to the variables in the different PLCs.