# Model Mediation to Overcome Light Limitations--Toward a Secure Tactile Internet System
## 4 Model Mediation
### Model Mediated Systems
#### 4.2.3 Recent Systems  
In [77], authors developed a model mediated system based on an impedance controller. The model mediated is employed at the master side, which is responsible for building a virtual environment for the slave side's environment and interacting with the master device. This communication between the virtual model and the end user takes place with almost zero delay. Moreover, it sends command signals to the slave side via the communication network. The slave side deploys an impedance controller that is used mainly for ensuring the slave device stability when interacting with surrounded environment as it compensates for force disturbance and instability matters concerned with the slave side. The slave side is fed with a contact-force estimator as the model assumes a light weight slave device with no force sensors. The output of the estimator is used to update the virtual model at the master side and also to modify and adapt the impedance controller. The system is experimentally tested for performance evaluation using a bilateral teleoperation system with a DoF of 3. The system employs a Novint's Falcon haptic device as the master device and a Geomagic's Phantom Desktop haptic device as the slave device [78; 79]. The system indicates a high performance in terms of stability and tracking. The system is tested for various communication delays in the communication network and the results indicates that the system stability almost unaffected by the communication delay which can be considered one of the main achievement of this work over the past model mediated systems. Even with the existence of worse communication delay the proposed model through the impedance control prevent the master device from receiving excessive forces. The system can be deployed for a variety of applications especially for those with a gradually changing remote environment with unknown or variable communication delays. The main disadvantage with this system is the nonexistence of force sensors on the slave device. Another issue is the thoughtlessness of a high-quality visual sensor. In [80], authors developed a model mediated system based on force updating algorithm and adaptive impedance controller. The force updating algorithm is introduced to overcome the force disturbance problem associated with the model updating, and thus achieves a higher level of system stability. The slave side employs an adaptive impedance controller, which can control the physical parameters of the slave side by comparing the expected model with the real environment. The system was mainly introduced to consider the stability issues associated with the teleoperated system and provide a stable human to machine interaction with acceptable experience. The system is experimentally tested to evaluate the controller performance, using a master device of a Geomagic Touch and the slave device of a translation parallel manipulator with a 3 DoF force sensor. The system is evaluated for 1 DoF with a constant delay of 5 s for different environmental materials. The controller achieves better efficiency intermesh of stability. The main limitation of this work is that it is dedicated only with one DoF tasks. The work also is tested for only a certain delay. In [81], authors developed a nonlinear predictor-based model mediated bilateral teleoperation system for robot-assisted surgery applications. The system mainly considered the time varying communication channels and was developed to compensate for the delay. The system is composed of two main loops or subsystems; one for the slave side, which is responsible for parameter estimation and the other, is for the master side which is responsible for the prediction as indicated in Figure 7.  
The environmental parameters are calculated in real time using log linearization technique and recursive least squares (RSL) method.