*2.4. Study Design*

This was a randomized crossover design whereby each volunteer came for five or nine test sessions with a minimum 1-day wash-out between sessions. The order of the study meals were randomized using the RAND function in Microsoft Excel. Volunteers were asked to avoid strenuous exercise and alcohol intake 24 h prior to their test session and to arrive at the center at 08:30 after an overnight fast of at least 10 h. Upon arrival, volunteers had their baseline (T0) blood pressure measured and a fasted blood sample drawn (after 5 min of rest) at the antecubital vein via cannula by a trained phlebotomist. Volunteers were then served the study meal and instructed to consume the meal within 15 min. Subsequent blood collection was carried out at T15, 30, 45, 60, 90, 120, 150, and 180 min after the first bite. Duplicate blood pressure measurements were taken hourly at T60, 120, and 180 min. A schematic of the study design is shown in Figure 1.

**Figure 1.** Schematic of study design.

#### *2.5. Blood Sampling and Analytical Methods*

Venous blood was collected in K2EDTA vacutainers (BD, New Jersey, NJ, USA), placed immediately on ice, and centrifuged at 1500× *g* for 15 min within an hour of blood draw to obtain plasma. Plasma samples were then stored at −80 ◦C in aliquots until ready for analyses. Plasma glucose and insulin concentrations were determined by the COBAS c311 and e411 automated analyzers (Roche Diagnostics GmbH, Berlin, Germany), respectively. For each analyzer, a successful two-point calibration was performed at the start of the study. Thereafter, quality control was done daily before analyzing the plasma samples. For each assay, 250 μL of thawed undiluted plasma was analyzed in a Hitachi cup using the manufacturer's recommended cassette for glucose and insulin measurement. All samples were analyzed over a 5-day period using the same analytical instrumentations and laboratory consumables (including standards and quality controls). All samples from a given individual (i.e., all treatments and all time points) were analyzed within the same batch and the same day, in order to limit any effects of experimental variations. The inter-batch coefficient of variation for glucose analysis was 7.51%, and that for insulin analysis was 1.99%.

## *2.6. Statistical Analyses*

The primary outcome of this study was the acute effects of the test ingredients on the postprandial glucose and insulin responses for up to 180 min. The secondary outcomes were: i) the effect of the form in which the test ingredients were administered (R vs. D) on the 30, 120, and 180 min postprandial glucose and insulin responses; and ii) the acute effects of the test ingredients on the postprandial blood pressure measured over 180 min. Incremental areas under the curve (iAUCs) of glucose and insulin were calculated using the change in glucose or insulin above baseline fasting concentration, ignoring the area beneath the baseline. Total areas under the curve (tAUCs) of systolic and diastolic blood

pressure measurements were calculated using the absolute blood pressure values measured at the time points.

All analyses in this study were done using Statistical Package for the Social Sciences (SPSS) version 24 (IBM, New York, NY, USA). Data were assessed for normality using the Shapiro–Wilk test as well as visually from the histogram and normal Q–Q (quantile-quantile) plots. Square-root transformation of the data was used where necessary to achieve normality. The treatment e ffect on the iAUCs of insulin and glucose was tested using linear mixed e ffects procedure in SPSS with treatment as the fixed factor and compound symmetry (CS) covariance structure. For the interaction between form and treatment test, a linear mixed e ffects procedure with both treatment and form as fixed factors was used with CS covariance structure.


**Chapter 4**

[80] Scott AP, Radom L. Harmonic vibrational frequencies: An evaluation of Hartree-Fock, Moller-Plesset, quadratic configuration interaction, density functional theory, and

Modern Spectroscopic Techniques and Applications

semiempirical scale factors. The Journal of Physical Chemistry. 1996;100:

16502-16513

56


*3.1. LCA Feeding Results in a Significant Upregulation of Genes Associated with Cholestasis, Inflammation, and Extracellular Matrix Remodeling*

Feeding of a chow diet supplemented with 1% LCA over 3.5 days (84 h) resulted in a severe cholestatic liver injury in wildtype (WT) mice, as described previously [21]. Liver tissue of LCA-fed WT mice was compared to chow-fed WT littermates by gene array analysis. In total, 332 and 263 genes were significantly up- or downregulated, respectively (*p* < 0.05; FDR-adjusted, and log2 fold change <−1.5 or >1.5; Supplementary Tables S1 and S2). Overrepresented Gene Ontology (GO) groups among the upregulated genes were associated with proliferation, inflammation, and extracellular matrix organization (Supplementary Tables S1 and S3, Figure 1). The four upregulated genes with the lowest *p*-values were the acute phase proteins serum amyloid A3 (Saa3) (46.2-fold up) and orosomucoid 2 (Orm2) (42.4-fold up), the bacterial siderophore binding protein lipocalin 2 (Lcn2) (32.4-fold up) that is expressed in neutrophils, and the pattern recognition receptor MARCO (macrophage receptor with collagenous structure, 17.4-fold up), which is found on macrophages and dendritic cells (Supplementary Table S1). The most significantly overrepresented GO groups among the downregulated genes were associated with oxidation-reduction processes, sodium-independent organic anion transport, and bile acid biosynthesis. The rate-limiting enzyme of bile acid synthesis, Cyp7a1 (89.0-fold down), was among the strongest downregulated genes (Supplementary Tables S2 and S4). Therefore, gene

expression profiling of the livers of mice under LCA diet revealed a profile of an inflamed, cholestatic organ undergoing extracellular matrix reorganization [21,22].

**Figure 1.** Influence of a chow diet supplemented with 1% lithocholic acid (LCA) over 3.5 days on gene expression in liver tissue of mice. (**A**) Heatmaps of z-scores (expression values standardized per gene to mean 0 and standard deviation 1) of the strongest differentially-regulated genes (*p* < 0.05 and log2 fold change >3 (upregulated) or <−3 (downregulated)). Each row corresponds to a gene, each column to a mouse. Rows and columns were ordered according to average linkage hierarchical clustering. (**B**) Volcano plot: On the x-axis, the log2 fold change is plotted, and on the y-axis, -log10 of the false discovery rate (FDR)-adjusted *p*-value is plotted.

We have previously reported that cholestatic liver injury in response to bile duct ligation is more severe in TGR5 knockout (KO) mice as compared to WT littermates [19]. Therefore, we analyzed liver damage following LCA feeding in TGR5 WT and TGR5 KO littermates.


*4.2. Atomic Layer Deposition of Conventional Lithium-Ion Battery Materials*

In this section, a few examples of the more conventional lithium-ion battery materials deposited by ALD are introduced. Examples of binary oxide electrodes (specifically V2O5 and TiO2) and lithium containing materials are presented. Lithium containing materials are quite a new addition to the ALD materials toolbox—the first paper on the subject was published in 2009 [70]. Since then, this area of research has expanded very rapidly. Due to the mobility and reactivity of Li+ ions, ALD of lithium containing materials has additional process development issues in comparison to most other ALD processes and some of these issues are discussed in the following subsections. In this section emphasis is given to potential solid electrolyte materials, as these are generally considered the most difficult materials to deposit. For a more thorough review of this subject, both review articles and books are available [71–79]. In recent years, ALD has also been studied extensively as a method to modify the interfaces between the electrodes and the electrolyte by forming an artificial SEI-layer [75,80,81]. ALD Al2O3 is generally used for this application and it has been found that a few ALD cycles can improve the cycling capability and capacity retention of the electrodes [80,81]. These results will not be discussed further here but the reader is advised that a lot of literature on this subject is available [80–83]. Some examples of ALD-made metal fluorides as artificial SEI layers will be shortly mentioned in Section 5.

#### 4.2.1. Cathodes

Table 4 includes examples of some of the conventional lithium-ion battery cathode materials deposited by ALD. Both binary and ternary oxides and phosphates have been deposited for conventional batteries. Li2S has been envisioned as a cathode for lithium-sulphur batteries [84].

**Table 4.** Examples of conventional lithium-ion battery cathode materials deposited by ALD. Abbreviations used: Oi Pr = *iso*-propoxide, Ot Bu = *tert*-butoxide, Cp = cyclopentadienyl, TMPO = trimethyl phosphate, thd = 2,2,6,6-tetramethyl-3,5-heptanedionato.

Vanadium oxide was one of the earliest materials to be deposited by ALD for lithium-ion batteries [85,86,92]. Vanadyl tris-*iso*-propoxide with either water or ozone as co-reactant have been used as precursors for this material. Using water produces amorphous films, while with ozone crystalline films can be obtained. Crystalline and amorphous films produce different capacities depending on the extent of lithium intercalation, with crystalline films having higher capacities when 1 or 2 Li-ions intercalate per one V2O5 unit [86]. A surprisingly high capacity of 455 mAh/g has been reported for 200 nm of amorphous V2O5 between 1.5 and 4.0 V (Li/Li+) [85]. This high value is related to the large potential range used for cycling, resulting in 3 Li-ions intercalating per one V2O5 [85]. For a thicker amorphous film of 450 nm, a capacity of 275 mAh/g was obtained in the same range. Both the thicker and the thinner films showed reasonable capacity retention after 90 cycles. For crystalline films, capacities of 127–142 mAh/g have been obtained in the potential range 2.6–4.0 (1 Li per V2O5) [86]. Between 1.5 and 4.0 V (3 Li per V2O5), a capacity of 440 mAh/g is obtainable but the capacity degrades to 389 mAh/g already in the second cycle.

As already discussed, lithium cobalt oxide LiCoO2 is currently the most often used cathode material in lithium-ion batteries. Despite this, only two reports from one group on the deposition of LiCoO2 by ALD can be found in the literature [87,88]. It appears that the challenges in cobalt oxide deposition have had an effect on the research of the lithiated material. The reported LiCoO2 process makes use of oxygen plasma combined with CoCp2 (cobaltocene) and LiOt Bu (lithium *tert*-butoxide). The deposition supercycle consists of Co3O4 and Li2CO3 subcycles and the effect of different pulsing ratios on film properties was studied. The process showed saturation with both metal precursors with Li:Co = 1:1 pulsing ratio and the film thickness increased fairly linearly with the number of cycles when using a 1:4 pulsing ratio. After annealing the films consisted of the hexagonal phase of LiCoO2 according to both Raman and GIXRD (grazing incidence X-ray diffraction) measurements. Electrochemical characterization revealed that a 12% capacity loss was evident between charge and discharge cycles. For a film deposited with a 1:4 pulsing ratio, the capacity was only about 60% of the theoretical value. For a 1:2 ratio film, the capacity was even lower, which might be explained by the higher impurity contents in this film. With the 1:4 pulsing ratio, the composition of the films was Li1.2CoO3.5, as determined by elastic backscattering [88].

The potential cathode material lithium iron phosphate, LiFePO4, has also been the subject of ALD studies [89,93] The material has been deposited at 300 ◦C on silicon substrates using ferrocene and ozone as precursors for the Fe2O3 subcycle, trimethylphosphate (TMPO) and water for PO*x* and lithium *tert*-butoxide and water for the Li2O/LiOH subcycle [89] Iron oxide and the phosphate were pulsed sequentially for five cycles, after which one cycle of Li2O/LiOH was applied. The resulting films were amorphous and showed a linear increase in thickness as a function of deposited supercycles. The material could also be deposited onto carbon nanotubes (CNTs) [87] The CNT-based films were amorphous but crystallization to orthorhombic LiFePO4 was observed after annealing in argon at 700 ◦C for 5 h. The Fe:P ratio in the annealed film was 0.9, as determined by EDX (energy-dispersive X-ray spectroscopy). Unfortunately, no compositional information on Li content was given. The LiFePO4 film deposited onto CNTs showed good electrical performance, with clear redox peaks in a cyclic voltammetry curve at 3.5 V and 3.3 V (vs. Li/Li+) and a discharge capacity of 150 mAh/g at 0.1 C [89]. Encouragingly, the material could maintain a discharge capacity of 120 mAh/g at 1 C even after 2000 cycles.

LiFePO4 has also been deposited using metal-thd complexes [93]. Pulsing Lithd (lithium 2,2,6,6-tetramethyl-3,5-heptanedionate) and ozone between subcycles of Fe(thd)3 + O3 and TMPO + O3 + H2O resulted in stoichiometric LiFePO4 when the fraction of Li2CO3 subcycles was 37.5%. The as-deposited films were amorphous but could be crystallized in 10/90 H2/Ar atmosphere at 500 ◦C. These films were reported to show poor electrical conductivity, as expected with this material [19], however very little additional information was given. It should be noted that the same research group has also published an ALD process for the de-lithiated cathode material FePO4 [94]. They reported an initial electrochemical capacity of 159 mAh/g for the as-deposited, amorphous 46 nm thick FePO4 film. The capacity increased to 175 mAh/g after 230 charge-discharge cycles and after 600 cycles the capacity was still 165 mAh/g.

Lithium manganese spinel Li*x*Mn2O4 is an interesting cathode material for lithium-ion batteries due to its low volume change during (de)lithiation, high voltage and environmentally benign elements. The material has been deposited by ALD by Miikkulainen et al. using various methods [90]. Firstly, Mn(thd)3 and ozone were used as precursors for manganese oxide and this process was combined with the Lithd + O3 process for lithium incorporation. Interestingly, even with exceedingly small numbers of Li2CO3 subcycles, high Li+ incorporation was achieved, with only a 5% Li2CO3 pulsing leading to a Li:Mn ratio of 1:1. This was in fact the maximum content of lithium obtained: using larger numbers of Li2CO3 subcycles led to a decrease in uniformity. To achieve the stoichiometric lithium level for LiMn2O4, 1% of Li2CO3 pulsing was sufficient. All the films showed the crystalline spinel phase as-deposited, with MnO2 impurities present in the films with the lowest lithium concentrations. Crystalline spinel LiMn2O4 was also obtained by using LiOt Bu and water as precursors, however little else was reported on this process.

The lithium manganese spinel process is unique in that while the growth rate of the films stays rather constant at below 0.3 Å/cycle, the lithium content increases very rapidly and reaches a high value with very small Li-subcycle numbers [90]. This indicates that the mechanism of this process differs significantly from conventional ternary ALD processes. Another clue about the mechanism was given by ToF-ERDA (time-of-flight elastic recoil detection analysis) elemental depth profiles which showed uniform film composition, albeit with a lithium deficiency on the film surface. To achieve such high lithium concentrations, either more than one monolayer should be deposited in one subcycle, or the growth should include a bulk component in addition to the normal surface reactions. Multilayer growth could be assumed to lead to lithium excess on the film surface, since lithium carbonate was always the last material deposited. Therefore, the bulk must be playing a role in the deposition process. Miikkulainen et al. postulated that the reduction needed for manganese to change from +IV in MnO2 to +III/+IV in LiMn2O4 takes place during the Lithd pulse, which affects not only the surface but also deeper parts of the film [90]. The following ozone pulse removes organic residues from the surface and re-oxidizes the topmost manganese ions on the surface. This reaction then drives lithium ions deeper into the film, resulting in a uniform elemental distribution with a slightly lithium deficient surface.

Miikkulainen et al. continued their studies on LiMn2O4, using both LiOt Bu and water and Lithd and ozone exposures on MnO2 at 225 ◦C [90]. Interestingly, 110 nm of manganese oxide could be converted to the spinel phase with only 100 cycles of the lithium carbonate process applied on top of the film. The carbonate was not present in the X-ray diffractogram. Lithiation was achieved to some extent also without ozone pulses. The manganese oxide films lithiated with LiOt Bu and water in a similar manner showed the best electrochemical storage properties, with a capacity of 230 mAh/g at 50 μA. The capacity retention was very good up to 550 cycles at 200 μA. Similar to LiMn2O4, vanadium oxide V2O5 could also be lithiated by pulsing either LiOt Bu and water or Lithd and ozone on top of the oxide film [90]. Using the Lithd and ozone precursors, lithium contents as high as 15 at% were obtained with only 100 cycles of the Li2CO3 process applied on the 200 nm oxide film.

Lithium sulphide, Li2S, is an attractive cathode material for high capacity lithium-sulphur batteries. It has recently been deposited by ALD [91] and requires inert atmosphere during sample handling to prevent reactions with ambient air, in a similar way to pure Li2O [95]. Li2S has been deposited using LiOt Bu and hydrogen sulphide between 150 and 300 ◦C. Unlike most lithium containing processes, this one produced a constant growth rate over the whole deposition temperature range studied. The refractive index of the films was much lower than the value for bulk crystalline Li2S, indicating a lower density of the films. The films were amorphous and could not be crystallized with annealing in inert atmosphere. Both XRF (X-ray fluorescence) and XPS (X-ray photoelectron spectroscopy) gave a Li:S ratio of 2:1, with no carbon contamination in the Li2S layer. Thus, the reaction between the precursors was very efficient. The Li2S films produced high capacities of 800 mAh/g when deposited onto mesocarbon microbeans and a somewhat lower capacity of 500 mAh/g when deposited directly onto a 2D Cu current collector. In both cases the Coulombic efficiency was ~100%, indicating that the material could indeed be used as a cathode in lithium-sulphur batteries. However, film thickness had a large effect on the capacity, with thicker films producing smaller capacities per gram, as Li2S is rather insulating. In addition, reactions with the copper current collector affected the charge-discharge profiles, indicating the formation of Cu*x*S.

#### 4.2.2. Anodes

Table 5 presents examples of lithium-ion battery anode materials deposited by ALD. The selection of materials is quite a bit more limited than in the cathode case, most likely illustrating the consensus that improvements in battery energy density are more easily obtained with improved cathode materials. ALD-made TiO2 has been studied as an anode material mostly in various 3D-constructions, illustrating the conformal coating ability of ALD [78,96–98]. Using 3D-structures the areal capacity of the titania anode can be greatly improved [96,97] Generally, TiO2 can intercalate 0.5 Li, resulting in a capacity of 170 mAh/g [97] However, using nanomaterials more lithium can be intercalated and capacities of 330 mAh/g have been obtained with anatase nanotubes with a wall thickness of 5 nm [98]. These nanotubes also showed excellent capacity retention.

**Table 5.** Examples of conventional lithium-ion battery anode materials deposited by ALD. Abbreviations used: Oi Pr = *iso*-propoxide, Ot Bu = *tert*-butoxide, thd = 2,2,6,6-tetramethyl-3,5 heptanedionato, TPA = terephthalic acid, LiTP = lithium terephthalate.

Attempts on the deposition of lithium titanate spinel, Li4Ti5O12, have been made using both titanium tetrachloride TiCl4 [99] and titanium tetra-*iso*-propoxide Ti(Oi Pr)4 as precursors [99–101]. In both cases, LiOt Bu was used as the lithium source and water was used as the oxygen source. Titanate

films deposited using TiCl4 reacted rapidly in air [99]. The films were amorphous as determined with X-ray diffraction and showed only very small amounts of lithium in ERDA measurements. In contrast, when using Ti(Oi Pr)4 as the titanium source and applying a long pulse time for this precursor, uniform titanate films with higher lithium contents could be deposited [99]. These films also reacted with air, however the reaction was much slower than when using TiCl4 as the titanium precursor. The growth rate of the films did not depend much on the pulsing ratio of the two metal precursors, being approximately 0.7 Å/cycle at 225 ◦C [99]. In another report using the same precursors, the growth rate was said to be slightly different at 0.6 Å/cycle at 250 ◦C [100]. For the process at 225 ◦C, ERDA measurements revealed that the lithium content of the films could be routinely tuned over a wide range by changing the metal pulsing ratio [99]. For example, with 33% lithium cycles the film stoichiometry was Li1.19TiO2.48 and the carbon and hydrogen impurity contents were low. XPS and ERDA revealed that in this material lithium was enriched on the film surface, most likely forming a carbonate layer: carbonate peaks were visible both in FTIR (Fourier transform infrared spectroscopy) and XPS [99,101]. Despite the carbonate formation, the films showed the Li4Ti5O12 spinel phase in XRD measurements also in the as-deposited state. The crystallinity could be improved by annealing in nitrogen at 640–700 ◦C. The annealed titanate films showed electrochemical activity but the capacity remained low at 40 mAh/g [101]. However, this low value might be related to uncertainties in the calculation of film mass. For the film deposited at 250 ◦C, the Li:Ti ratio was reported as 2:1 with 44% lithium pulsing [100], which could indicate Li2TiO3 formation—a well-known impurity phase for Li4Ti5O12 [103,104]. After annealing in argon at 850 and 950 ◦C these films showed XRD peaks belonging to Li4Ti5O12 [100].

In addition to purely inorganic materials, ALD can also be used to deposit hybrid materials using organic molecules as the second precursor [105]. Lithium terephthalate (LiTP) has been deposited using Lithd and terephthalic acid as precursors between 200 and 280 ◦C [102]. This material has been proposed as a possible Li-ion battery anode due to its high theoretical capacity of 300 mAh/g and a low potential of 0.8 V (vs. Li+/Li) [106]. The ALD process for LiTP showed saturation but no ALD window or constant growth rate as a function of the number of cycles [102]. The changing growth rate, accompanied by changes in the film density, could be related to the island growth mechanism of the film. The films were crystalline as deposited, which is unusual for ALD hybrid films. The films were electrochemically active and showed high rate capabilities with good capacity retention. The electrochemical properties of the films could further be enhanced by a protective LiPON layer on top of the electrode. The higher than theoretical capacity of 350 mAh/g is partly explained by difficulties in determining the electrode film thickness in electrochemical analyses. Recently, this anode material was combined with an organic cathode material dilithium-1,4-benzenediolate to produce a functioning atomic layer/molecular layer deposited thin film battery [107].


*Review* **Human–Robot Collaboration in Manufacturing Applications: A Review**

**Eloise Matheson 1, Riccardo Minto 2,\*, Emanuele G. G. Zampieri 2, Maurizio Faccio 3 and Giulio Rosati 2**

Received: 30 September 2019; Accepted: 3 December 2019; Published: 6 December 2019

**Abstract:** This paper provides an overview of collaborative robotics towards manufacturing applications. Over the last decade, the market has seen the introduction of a new category of robots—collaborative robots (or "cobots")—designed to physically interact with humans in a shared environment, without the typical barriers or protective cages used in traditional robotics systems. Their potential is undisputed, especially regarding their flexible ability to make simple, quick, and cheap layout changes; however, it is necessary to have adequate knowledge of their correct uses and characteristics to obtain the advantages of this form of robotics, which can be a barrier for industry uptake. The paper starts with an introduction of human–robot collaboration, presenting the related standards and modes of operation. An extensive literature review of works published in this area is undertaken, with particular attention to the main industrial cases of application. The paper concludes with an analysis of the future trends in human–robot collaboration as determined by the authors.

**Keywords:** collaborative robotics; cobots; human–robot interaction; literature review

#### **1. Introduction**

Traditional industrial robotic systems require heavy fence guarding and peripheral safety equipment that reduce flexibility while increasing costs and required space. The current market, however, asks for reduced lead times and mass customization, thus imposing flexible and multi-purpose assembly systems [1]. These needs are particularly common for small- and medium-sized enterprises (SMEs). Collaborative robots (or cobots [2]) represent a natural evolution that can solve existing challenges in manufacturing and assembly tasks, as they allow for a physical interaction with humans in a shared workspace; moreover, they are designed to be easily reprogrammed even by non-experts in order to be repurposed for different roles in a continuously evolving workflow [3]. Collaboration between humans and cobots is seen as a promising way to achieve increases in productivity while decreasing production costs, as it combines the ability of a human to judge, react, and plan with the repeatability and strength of a robot.

Several years have passed since the introduction of collaborative robots in industry, and cobots have now been applied in several different applications; furthermore, collaboration with traditional robots is considered in research, as it takes advantage of the devices' power and performance. Therefore, we believe that it is the proper time to review the state of the art in this area, with a particular focus on industrial case studies and the economic convenience of these systems. A literature review is considered

a suitable approach to identify the modern approaches towards Human–Robot Collaboration (HRC), in order to better understand the capabilities of the collaborative systems and highlight the possible existing gap on the basis of the presented future works.

The paper is organized as follows: After a brief overview of HRC methods, Section 2 provides an overview of the economic advantages of the collaborative systems, with a brief comparison with traditional systems. Our literature review analysis is presented in Section 3, and Section 4 contains a discussion of the collected data. Lastly, Section 5 concludes the work.

#### *Background*

Despite their relatively recent spread, the concept of cobots was invented in 1996 by J. Edward Colgate and Michael Pashkin [2,4]. These devices were passive and operated by humans, and are quite different from modern cobots that are more represented by the likes of lightweight robots such as KUKA LBR iiwa, developed since the 1990s by KUKA Roboter GmbH and the Institute of Robotics and Mechatronics at the German Aerospace Center (DLR) [5], or the first commercial collaborative robot sold in 2008, which was a UR5 model produced by the Danish company Universal Robots [6].

First of all, we believe that it is important to distinguish the different ways of collaboration, since the term collaboration often generates misunderstandings in its definition.

Müller et al. [7] proposed a classification for the different methodologies in which humans and cobots can work together, as summarized in Figure 1, where the final state shows a collaborative environment.

It should be noted that neither this classification nor the terminology used are unique, and others may be found in the literature [8–11].

**Figure 1.** Types of use of a collaborative robot.

To provide definitions and guidelines for the safe and practical use of cobots in industry, several standards have been proposed. Collaborative applications are part of the general scope of machinery safety regulated by the Machinery Directive, which defines the RESS (Essential Health and Safety Requirements). For further documentation, we refer to [12].

The reference standards as reported in the Machinery Directive are:

• UNI EN ISO 10218-1:2012 "Robots and equipment for robots, Safety requirements for industrial robots, Part 1: Robots".

In an international setting, the technical specification ISO/TS 15066:2016 "Robots and robotic devices, Collaborative Robots" is dedicated to the safety requirements of the collaborative methods envisaged by the Technical Standard UNI EN ISO 10218-2:2011.

According to the international standard UNI EN ISO 10218 1 and 2, and more widely explained in ISO/TS 15066:2016, four classes of safety requirements are defined for collaborative robots:

Collaborative modes can be adopted even when using traditional industrial robots; however, several safety devices, e.g., laser sensors and vision systems, or controller alterations are required. Thus, a commercial cobot that does not require further hardware costs and setup can be a more attractive solution for industry.

Lastly, cobots are designed with particular features that distinguish them considerably from traditional robots, defined by Michalos et al. [13] as technological and ergonomic requirements. Furthermore, they should be equipped with additional features with respect to traditional robots, such as force and torque sensors, force limits, vision systems (cameras), laser systems, anti-collision systems, recognition of voice commands, and/or systems to coordinate the actions of human operators with their motion. For a more complete overview, we refer to [8,13]. Table A1 shows the characteristics of some of the most popular cobots, with a brief overview of some kinematic schemes in Table 2.

#### **2. Convenience of Collaborative Robotics**

The choice towards human–robot collaborative systems is mainly dictated by economic motivations, occupational health (ergonomics and human factors), and efficient use of factory space. Another advantage is the simplification in the robot programming for the actions necessary to perform a task [14]. In addition, learning by demonstration is a popular feature [15].

Furthermore, the greater convenience of collaborative systems is their flexibility: Theoretically, since collaborative cells do not require rigid safety systems, they could be allocated in other parts of plants more easily and more quickly; therefore, they could adapt well to those cases in which the production layout needs to change continuously [16]. However, it should be noted that high-risk applications have to be constrained as in any other traditional system, thus restricting the flexibility.

Collaborative systems can also achieve lower direct unit production costs: [17] observed that a higher degree of collaboration, called *c*%, has a high impact on throughput; moreover, depending on the assembly process considered, the throughput can be higher than in traditional systems.

Table 1 provides a comparison between collaborative and traditional systems for four different jobs: assembly (the act of attaching two or more components), placement (the act of positioning each part in the proper position), handling (the manipulation of the picked part), and picking (the act of taking from the feeding point). In order to adapt to market needs, a manual assembly system could be used, though this can lead to a decrease in productivity due to variations in quality and fluctuations in labor rates [18]. Comparing the human operator capabilities to automated systems, it is clear that the performance of manual assembly is greatly influenced by ergonomic factors, which restrict the product weight and the accuracy of the human operator [19]. Therefore, these restrictions limit the capabilities of human operators in the handling and picking tasks of heavy/bulky parts. These components can be manipulated with handling systems such as jib cranes: These devices could be considered as large workspace-serving robots [20], used for automated transportation of heavy parts. However, to the authors' knowledge, there are no commercial end-effectors that allow these systems to carry out complex tasks, such as assembly or precise placing, since they are quite limited in terms of efficiency and precision [21].

Traditional robotic systems [22] bridge the presented gap, presenting manipulators with both high payload (e.g., FANUC M-2000 series with a payload of 2.3 t [23]) and high repeatability. However, the flexibility and dexterity required for complex assembly tasks could be too expensive, or even impossible, to achieve with traditional robotic systems [24]. This gap can be closed by collaborative systems, since they combine the capabilities of a traditional robot with the dexterity and flexibility of the human operator. Collaborative robots are especially advantageous for assembly tasks, particularly if the task is executed with a human operator. They are also suitable for pick and place applications, though the adoption of a traditional robot or a handling system can offer better results in terms of speed, precision, and payload.

**Table 1.** Qualitative evaluation of the most suitable solutions for the main industry tasks.

#### **3. Literature Review**

This literature review analyses works from 2009–2018 that involved collaborative robots for manufacturing or assembly tasks. Reviewed papers needed to include a practical experiment involving a collaborative robot undertaking a manufacturing or assembly task; we ignored those that only considered the task in simulation. This criterion was implemented as, often, only practical experiments with real hardware can highlight both the challenges and advantages of cobots.

For this literature review, three search engines were used to collect papers over our time period that were selected using the following boolean string: ((collaborative AND robot) OR cobot OR cobotics) AND (manufacturing OR assembly). Our time period of 2009–2018 was chosen as the timeline for this literature review, as it is only in the last 10 years that we have seen the availability of collaborative robots in the market.

Of all these relevant results, 16 were duplicated results, leaving us with 113 papers to analyze. Upon a complete read-through of the papers, 41 papers were found to fully fit our criteria and have been included in this review. It should be noted that in the analysis regarding industry use cases, only 35 papers are referenced, as 6 papers were focused on the same case study as others and did not add extra information to our review.

The following parameters were studied: The robot used, control system, application, objectives, key findings, and suggested future work for all these studies, as summarized in Table 3. These were chosen for the following reasons. The robot choice is important, as it highlights which systems are successfully implemented for collaborative applications. The control system is interesting to analyze, as it dictates both safety and performance considerations of the task. Furthermore, when a human is in the control loop, the control system choice is specific to the manner of human–machine interaction by seeing which methods are more popular and successfully implemented, we can identify trends and future directions. We characterized control systems as vision systems (such as cameras and laser sensors), position systems (such as encoders which are typical of traditional industrial robots), impedance control systems (through haptic interfaces), admittance control (taking advantage of the cobot torque sensors or voltage measurement), audio systems (related to voice command and used for voice/speech recognition), and other systems (that were not easily classified, or that were introduced only in one instance).

The application represents the task given to the cobot, which we believe allows a better understanding to be made regarding the capabilities of collaborative robots. These tasks were divided into assembly (when the cobot collaborates with the operator in an assembly process), human assistance (when the cobot acts as an ergonomic support for the operator, e.g., movable fixtures, quality control, based on vision systems), and lastly, machine tending (when the cobot performs loading/unloading operations).

Furthermore, we divided the objectives into three main topics: Productivity, representing the studies focused on task allocation, quality increase, and reduction of cycle time; safety, which includes not only strictly safety-related topics such as collision avoidance, but also an increase in human ergonomics and reduction of mental stress; and HRI (Human–Robot Interaction), which is focused on the development of new HRI methodologies, e.g., voice recognition. It should be noted that in no way is the proposed subdivision univocal; an interesting example could be [25–27]. These works were considered as safety because, even if the proposed solutions keep a high level of productivity, they operate on HRC safety.

The key findings were not grouped, since we believe they depend on the specific study and are too varied; however, they have been summarized in Table 3. Key findings were useful to present the capabilities of the collaborative systems and what HRC studies have achieved. They were included in our analysis in order to identify common solutions. Future work has been grouped into: HRI (works that focus on increasing HRI knowledge and design), safety (works that focusing on increasing the operator safety when working with the cobot), productivity (works focusing on increasing the task productivity in some manner), task complexity (works that focus on increasing the complexity of the task for a particular application), applicability (works that focus on increasing the scope of the work to be used for other industrial applications), and method (works that focus on enhancing the method of HRI via modeling, using alternative robots, or applying general rules and criteria to the design and evaluation process). From these groupings, we can identify ongoing challenges that still need to be solved in the field; by seeing what researchers identify as future work for industrial uptake, we can find trends across the industry in the direction research on which is focused. Our analysis of these parameters is presented in Section 4.

#### **4. Discussion: Trends and Future Perspective**

#### *4.1. Trends in the Literature*

By examining the literature as summarized in Table 3, we can identify several trends in the use of cobots in industrial settings. It should be noted that, for some of the considered studies in Table 3, we could not identify all of our parameters as specified in Section 3; thus, they are not considered in this specific discussion.

Although early researches utilized traditional industrial robots (Figure 2), the subsequent spread of cobots led to several studies based on the DLR LWR-III (2011), followed by the upgraded KUKA iiwa (from 2016 to 2018), ABB YuMi (also called FRIDA) in 2017 and 2018, and Universal Robots from 2014 to 2018. Several researchers applied the collaborative methods to industrial robots, usually due to their increased performance and widespread availability; however, the disadvantage of this choice is the increase in cost and complexity due to the inclusion of several external sensors and the limited HRC methodologies available. A relationship between the kinematics of the cobot and the application was not explicitly considered, since we believe that other parameters, such as the presence of force sensors in each axis, influenced the cobot choice made in these papers. However, it should be noted that the kinematics—precisely, the number of axes—was a feature considered in [28], whereas future works are focused on verifying their findings with kinematically redundant robots [29] or utilizing the redundancy for achieving better stiffness in hand-guiding [30].


**1. Introduction**

Lviv National Academy of Arts (LNAM) is a Lviv art educational institution for the training of specialists in the applied arts. Tradition and experience of artists of the University's predecessors, it is worth noting illustrators, book designers and periodicals for children: Sofia Karaffa-Korbut, Ivan Ostafiychuk, Zenovia Yuskiv, Lubomyr Medvid, they have become a good artistic basis for the younger generation. In turn, the younger generation is absorbing new trends of the postmodern era, testing various kinds of artistic and technical performance, increasingly taking into account the wishes of society. We can talk about a close relationship—artist—publisher—reader. A new and unpredictable philosophical thought in the expression of their ideas—the

concept of a new children's book. Consider the creative work of contemporary artists: Maryana Kachmar (Flyak), Khrystyna Reynarovych, Anastasia Stefurak, Andriy Lesiv and Romana Romanyshyn (Creative Tandem "Agrafka").

Illustrative artists who collaborate with modern publishers and offer them bold graphic designs of works by Ukrainian and foreign writers. Author's innovative graphic solutions of covers, covers of the edition. Artists are bold in their vision of the book as a whole, the design of the book can be changed to a non-classical design, or the illustration will be created beyond the usual format of design [1].

The general tendencies in drawings will be traced, when often the image is decorative plane, there is an ornament and a decor. Graphic solution of illustrations found in Easter painting, icon painting, weaving and painting of ceramics, enamels. Artists who imitate the decoration of things and everyday life of decorative and applied use.

There are conceptual approaches of modern illustrators of children's publications, which were formed in the general educational environment—in LNAM. The plurality of authorial approaches in the interpretation of classical literary forms or innovations in different versions of the esthetics of modern book graphics will be considered. Graduates of the Department of Graphic Design and other departments of LNAM, cooperate with various publishers, including: "Kamenyar", "Apriori", "Old Lion Publishing House", "Svichado", "Svit", implement original formal ideas.