# In-Plane Material Handling: A Systematic Review
## 3 Results
### Answer to RQ2
The first [80] exploits ultrasonic piezo-actuators to move microscopic and mesoscopic parts, while the second employs distributed cell plates, also with longitudinal vibrations, to handle meso- and macro-scale objects. Finally, in [49, 50], a longitudinal wave-saw tooth vibrating surface was used for micro-part displacement, while in [81] the two types of vibrations were combined in a parallel mechanism-based platform to manipulate mesoscopic parts. Thirdly, ciliary surfaces are suited for light microscopic and mesoscopic parts with at least one major planar surface. They exploit a step-by-step contact motion achieved d by the bending of flexible cilia [11, 64] or the combined rotary movement of eccentric cilia-inspired bodies [36]. Their use is directed more towards biomedical applications, e.g., manipulation of fluids [11] and research. Moving on, the fourth technology presented in Figure 6 is mobile platforms. Like vibrating surfaces, this class of devices is employed for different sizes of materials, and in some specific cases, mobile platforms can also deal with heavier objects. These systems mostly work with planar parts; however, there are a few solutions that can also move curved items [62, 63, 69]. Specifically, such devices have the common characteristic of being composed of swarms of mobile robots that can cooperate to surround and handle components. Therefore, given this capability, requirements with respect to the shape of the object are less stringent, and planarity is not required. Additionally, these solutions excel in handling heavier parts, especially considering that most of the other platform solutions  
Figure 6: Smart surface classification (adapted from [73]). identified in the review primarily consist of electromagnetic stages designed for micro-conveyance. On this subject, in [10; 44; 46; 47; 48], similar driving coils were assembled into platforms capable of micro-displacements on top of arrays of permanent magnets. In [45; 72], grids of tiny collaborative platforms confined in shaped housings worked together to move planar objects on top by micro-steps, similar to ciliary motion. Finally, in [61], controlled platform accelerations and tilting were used to move a small (mesoscopic) object on top. Continuing with the technology categories outlined in Figure 6, the next one involves pneumatic systems. This class of devices is employed for contactless transport of different sizes of light planar objects. The fields of application include manufacturing and intralogistics, especially concerning small (micro/meso-scale) and fragile parts [75] like silicon wafers [82]. The majority of the retrieved solutions involve the utilization of MEMS technology to develop modular grids of nozzles with adjustable openings, allowing for control of the direction of air jets. Main research on the topic includes the _Smart Surface_ Project, which involved five French teams and one Japanese team building on studies initiated by [PERSON] and [PERSON] [17] and [PERSON] et al. [83]. This project is referenced in several works [21; 24; 30; 41; 42; 43; 71; 75; 84]. Similarly, another solution with air jets but without MEMS, was presented in [40], where the array for the distributed manipulation contained modules with a central electrode that can open and close the nozzles with electrostatic actuation. As an alternative, other research has focused on different techniques exploiting pressure fields. In [33; 34; 35; 85], a manipulator for planar parts comprising platforms was studied. In practice, the bottom platform serves as an air bearing, while the top one is capable of creating air sinks to generate flows and, thus, handle forces. In [54; 55; 86], a similar concept but with only one plane was developed. Specifically, the manipulator comprises an array of tubes used to both blow air to support an object and to produce a vacuum to move it.