# Touch, Texture and Haptic Feedback: A Review on How We Feel the World around Us
## 4 Haptic Feedback
### Kinesthetic Feedback  
Most kinesthetic feedback devices rely on actuators generally attached to either the hands or the arms that detect movement and apply an appropriate feedback force to that area to either admit or impede movement [78; 90; 91; 92; 93; 94; 95; 96] and to simulate various motion types such as gripping and lifting of objects. Unlike cutaneous feedback which has actuators capable of stimulating the mechanoreceptors directly, such as in electrotactile or temperature-based feedback, kinesthetic feedback systems mostly rely on force feedback which generally requires the use of large actuators to apply the appropriate force to the user. Kinesthetic feedback can be categorized into two main types, grounded and exoskeleton-based devices. Grounded force feedback systems are described as feedback systems which are mounted onto a stationary platform where the user is either attached to or holds an end effector which tracks the user's position while modulating the amount of force that is being applied. Exoskeleton-based feedback systems use actuators that are mounted onto and/or attached to the user's body, usually their arms or hands, and are ungrounded. Different actuators have been used throughout the development history of kinesthetic feedback systems. Early kinesthetic feedback systems made use of hydraulic systems placed on exoskeleton devices attached to the arms [97; 98]. These devices, however, were often bulky and difficult to use, preventing use outside of laboratory settings. After hydraulic actuators, pneumatic actuators eventually saw more uses in kinesthetic feedback systems due to their lightness, which allowed for less bulky and more comfortable suits [99; 100]; however, the prerequisite requirement of needing a source for pressurized fluid is still a major issue. Advances in technology have allowed for the creation of smaller actuators leading to the creation of lighter and smaller kinesthetic feedback systems allowing for a better form factor when equipped on the hands. Both Dexmo and Maestro make use of a number of motors attached to movable end effectors and synthetic fiber, respectively, as their braking system [95; 101]. Cable-based actuators have also seen rising popularity, largely due to being lightweight in form factor and the flexible nature of the cable allowing for better motor placements without obstructing hand movement. Cybergrasp utilizes a series of cables attached to motors that pull the strings to prevent finger movement [102]. ExoTen uses a twisted string actuator system for its kinesthetic feedback system, with the twisted  
Figure 2: The proposed workflow of a haptic feedback system. (**a**) shows the tactile stimuli that is received by the mechanoreceptors, (**b**) the tactile sensor converts the same stimuli into data before (**c**) recreates the same feedback sensation. string actuator design allowing for high load outputs while using significantly smaller DC motors [78]. LucidVR also uses a string actuator attached to a series of servo motors as its braking system but with a more modular design owing to it being open source [77]. Aside from more traditional feedback systems such as hydraulics, pneumatics, and motors, there have also been more specialized braking systems that have also seen use and research. SenseGlove uses magnetic brakes instead of traditional motors to transmit force between the wires and the fingertips [103]. Dextres uses a novel electrostatic braking system for its feedback system by using two metal strips and taking advantage of the differences in electrostatic attraction between the two strips to create electrostatic friction [93]. Research has also been carried out regarding the use of soft materials for use in hand exoskeletons. [PERSON] et al. made use of McKibben muscles as their primary actuator which closely mimics human muscle and has a low force-weight ratio [104]. Recently, research regarding the use of fiber jamming in robotics has also increased.