## 2 Building a Model of a Robotic System  
The work [13] shows the effectiveness of automated aliquoting compared to manual labor. Research in the field of application of robotic systems for liquid dosing and automation of laboratory processes for sample preparation is carried out by many scientists. Active research is being conducted at the Institute of Automation and Center for Life Science Automation, University of Rostock (Rostock, Germany). In works [14; 15], the use of a cognitive two-handed robot, working in conjunction with an operator and remotely controlled, is proposed. Pipetting of liquid is carried out with an automatic hand-type pipette, widely used in laboratory practice. Each robot arm has 7 degrees of freedom and can perform any manipulations within the workspace. The disadvantage of this solution is the low speed of the end-effector and the low accuracy of its positioning. So, in [16], an integrated system based on robots is considered for automating a multistage system of laboratory research, including the movement of equipment and biomaterial samples. The possibility of integrating devices controlled through electronic interfaces such as RS232, USB, Firewire, or Ethernet into a common network is shown, which allows centralized control of the technological process. The article discusses a new architecture and design of a robotic system, which must meet the following requirements to ensure the technological process of aliquoting:  
1. The volumes of the tubes used: from 2 mL to 9 mL, the height of which is 75 and 100 mm, respectively (Figure 1). 2. The volumes of the pipettes used are from 10 \(\mu\)L to 5000 \(\mu\)L, the height of which is from 32 mm to 150 mm. 3. A rack for loading tubes with fractionated whole blood samples should hold 12 or more tubes with a volume of 9 mL. 4. The height of the manipulator workspace must be bigger than the sum of the maximum volume tube height (100 mm), maximum pipette height (150 mm), and the safe distance between the tube and the pipette. The safe distance is 100 mm. Thus, the height of the manipulator workspace should be 350 mm. 5. Initially, the liquid is divided into fractions. The movement of tubes with samples of whole blood, divided into fractions, should be carried out evenly and progressively in the horizontal direction, limited by the velocity of the mechanism and in the vertical direction--no more than 0.03 m/s, without sudden movements (to prevent the risk of breaking the integrity of the clot blood). 6. The robotic system must meet the requirements for the safety of human-robot interaction. So, all movements of the robot should be stopped when human limbs enter the workspace to avoid injury. The flow chart of the aliquoting process is shown in Figure 2.  
Figure 3 shows a 3D model of a robotic system, which includes a parallel DeLi manipulator with 4 degrees of freedom, made based on the Delta mechanism and equipped with an excavating head for performing basic operations for aliquoting biomaterial, and a collaborative robot (Uni) with a serial structure for performing transportation operations,  
Figure 1: Round bottom blood tubes. Figure 2: Aliquoting process. racks with test tubes and plates, and microtubes. Uni robot is used for the stage when liquid is divided into fractions. The DeLi robot should take only one upper fraction from a test tube and distribute it into smaller tubes, while not allowing the lower fraction (sediment) to enter. After taking the desired fraction, the DeLi robot can move at any speed available to this type of robot. The amount of the withdrawn fraction is determined using the developed technical vision system, which is not described in this work. The DeLi manipulator dispenses only one fraction of blood; therefore, the velocity for the DeLi manipulator is not limited. The Delta parallel robot topology has been chosen due to the fact that it has a better performance in terms of dynamics and accuracy as compared with serial robots.