# In-Plane Material Handling: A Systematic Review
## 3 Results
### Answer to RQ1  
After an introduction of general information about the review, the focus can finally move to the research questions. The answer to the first research question (RQ1) is presented in the following paragraphs. This research focused on which in-plane transport and manipulation systems have been studied to enhance their flexibility and adaptability for typical handling tasks. Upon initial examination of the literature, it became evident that numerous solutions have been  
Figure 3: Types of publications retrieved. Figure 2: Papers published per year. explored over the years, encompassing various technologies, fields of application, and handled material sizes. Examining its evolution in the literature, the concept of in-plane multi-directional manipulation for enhanced flexibility originated with microscopic applications and the advancement of Micro-Electro-Mechanical Systems (MEMSs) [21,24]. Specifically, [PERSON] et al. [25] were among the first to propose an MEMS to move parts in a 2D space using ciliary motion. Their research, followed by that of many others, such as [PERSON] et al. [18,19,26], [PERSON] et al. [6], and [PERSON] et al. [27], aimed to exploit grids of actuators realized on semiconductor plates to control object motion (Figure 4a). Practically, their idea was to use the friction forces created by tilting cantilevers to transport and handle a part on top. At the same time, [PERSON] et al. [28] and [PERSON] et al. [20] also worked on similar surfaces with distributed manipulation but used vibrations to handle micro parts. In their approach, they aimed to control the vibration frequencies of one [28] (Figure 4b) or more plates [20], utilizing the attraction of parts towards the plate's vibration nodes for manipulation. In the same line of interest for distributed and programmable handling, different technologies emerged in the literature during that period. For example, [PERSON] et al. [9,31] proposed the use of actuated rotors to move macroscopic objects (packages) (Figure 4c), while [PERSON] et al. [17] promoted the use of air jets for contactless micro-conveyance (Figure 4d). Starting with the rotor solution, [PERSON] et al. created an array of cells, each containing two perpendicular, motorized, omnidirectional wheels. A planar object placed on top of this array was supported by many cells, each able to generate an oriented friction force resulting from the two wheels' speed control. On the other hand, the pneumatic solution exploits MEMS, but in this case, the mobile cantilevers open or close valves to regulate air jets (Figure 4d). As a result, the surface is made up of smart modules created with this technology, acting together to achieve contactless object motion. Figure 4: Some in-plane handling technologies used over the years. (**a**) MEMS surface based on [27]; (**b**) vibrating platform [29]; (**c**) cell with rotors [2]; (**d**) pneumatic solution [30]. Among these initial studies, investigations also extended to the types of force fields that surfaces can generate. Approximately between the years of 1997 [32] and 2006 [33], interest was focused on automatically orienting and conveying parts [19; 26; 32; 33; 34; 35] using sensorless solutions [28]. Later, with advancements in sensors and computing power, interest shifted to refined control strategies to accomplish more complex tasks, such as position or trajectory tracking [4; 36; 37]. In this regard, cameras [5; 38] or distributed sensors [39], regardless of the actuation method employed for handling, are preferred, as they provide information over wider areas. As control technologies evolved, the involved technologies progressed as well. Consequently, MEMS solutions once employed for micro-conveying were replaced by pneumatic surfaces [30; 40; 41; 42; 43] and electromagnetically actuated moving platforms [10; 44; 45; 46; 47; 48]. Alternatively, other studies have utilized vibrating [29; 49; 50; 51] and non-MEMS ciliary [36] solutions for micro-conveyance.