Before I go over what a collaborative robot is, I will present the definition of automation, including robotization. According to M. Pawlak [1], automation (from the Greek automatos, i.e. automatic) is a process of relieving or completely reducing human physical and mental work using machines and devices that perform repetitive activities automatically. This process is possible only “with the use of modern solutions in the broadly understood field of industrial automation, which is constantly evolving.” According to another author [2], automation is an industrial process where all possible operations that are performed are transformed from a manual process to automated or mechanized. To a large extent, the first and the second definition refer to our issues related to production processes, which consist in the production of physical parts and entire machines and devices (machining, assembly).

In the definition [1], it should be noted that automation without the use of robots primarily covers the field of software, decision-making, optimization, process planning, process automation, production resource planning, e-services, accounting and financial work, communication [3]. Automation as a word has a very capacious meaning and therefore it is necessary to specify the area taken. In the article Automation of the machining station, in the introduction, I referred to an article by the strategic consulting company McKinsey & Company published in the Production Manager magazine, in which it was stated that the estimates for 2019 indicate the potential of work automation in Poland – as much as 49% of working time (approx. 3 million full-time jobs!) occupy activities that can be automated on the basis of existing technologies.

Collaborative robot [www1] (fig. 1 and 2), specifically Universal Robots Cobots, as an innovative project, was created in 2005 in Denmark. The originators were students who wanted to construct a device that could replace people in various tasks set by the industry. A necessary condition, somewhat parallel, was the development of a device safe for the operator, which can be programmed by anyone, not only by a highly qualified programmer or automation engineer.

Fig.1. An example of a robotic machining station using a collaborative robot – Abplanalp’s stand during international fair STOM 2019.

Fig. 2. Example of a robotic machining station with a cooperating robot – Yamazaki MAZAK during international fair STOM 2022

Safety of industrial robots and cobots

In the case of “traditionally” understood industrial robots, the operator cannot be in the same working zone together with the industrial robot (Figures 3 and 4). Figure 4 shows an educational assembly station (Faculty of Mechanical and Industrial Engineering of the Warsaw University of Technology), and Figure 4 shows an example of a robotic machining cell presented at the OKUMA stand during STOM 2019.

Fig. 3. Educational automated learning station (FMIE WUT).

Fig. 4. Demonstration robotic machining cell by OKUMA – international fair STOM 2019.

Physical protective barriers and light curtains were used at the stations presented in Figures 3 and 4. Formally, the so-called Machine Directive No. 2006/42/EC (Machine Directive – MD), the exact name of which is: Directive 2006/42/EC of the European Parliament and of the Council of May 17, 2006 on machinery, amending Directive 95/16/EC. Therefore, all machinery and equipment installed in the European Union must meet the basic health and safety requirements, which are described in Annex I to this directive. Within this legal act, the standards ISO 10218-1, ISO 10218-2 and ISO 13849-1 were also harmonized. It is assumed that if a machine or device meets the requirements of such a harmonized standard, it also meets the essential requirements of the Machinery Directive itself [www2].

The collaborative robot is dedicated to direct human-robot interaction in a shared workspace and where the operator and robots are in close proximity to each other. For a certain period of operation of cooperating robots in industrial conditions, the provisions on occupational health and safety of the relevant regulations for cobots [www1 and www2].

In February 2016, the ISO standards for traditional industrial robots were extended to include a technical specification for collaborative robots. The International Organization for Standardization (ISO) has published new technical specifications:

• ISO/TS 15066 supporting the ISO 10218-1 document known as “Safety Requirements for Industrial Robots”;
• ISO 10218-2 – Safety requirements for robotic systems and integration.

The ISO/TS 15066 specification provides guidance on how to ensure safety when designing and implementing robotic applications. According to the provisions of the ISO 10218 standard, in order for the robot to be able to cooperate with the operator (human), it must meet several key conditions. First of all, the robot must be equipped with an emergency stop (E-stop button). As with any other machine and device, in the event of a dangerous situation, we can stop the robot’s operation by pressing the emergency shutdown button. Secondly, the control system of an industrial robot should monitor not only emergency shutdowns, but also: the speed and position of the robot, and if necessary be able to limit these values. Thirdly, the operator should have access to the option of manually guiding the arm. As part of responding to the occurrence of various states during the robot’s operation, the option of limiting the arm’s power and force should also be available [www2, www3].

According to the ISO/TS 15066 specification, not only the robot, but the entire robotic system, including the objects it works on and additional tools, must meet the applicable safety standards. From the point of view of the implementation of collaborative robots, there are provisions of section 5.4 of the ISO 10218-1 standard, which defines the safety requirements for control systems. They should be designed to meet the performance level requirements with a Category 3 (Performance Level – PL=d) structure in accordance with ISO 13849-1 (Section 5.2.2 of the aforementioned ISO 10218-1). A solution according to a certain level of performance and risk assessment is acceptable (ISO 10218-1 section 5.2.3). The ISO/TS 15066 specification contains valuable comments and recommendations related to risk assessment, intended for integrators dealing with the implementation of collaborative robots.

Category 3 means a system constructed with double protection. A single error/defect cannot lead to the loss of a safety function. The ISO/TS 15066 specification also contains recommendations as to the permissible forces that may affect individual parts of the human body. On the one hand, the standards are not mandatory acts, but rather a set of recommendations on what features a device should have. However, the Machinery Directive 2006/42/EC [www2] is mandatory.

Collaborative robot – safe solutions

The collaborative robots of the Danish company Universal Robots, a precursor in this field, have as many as 17 built-in safety functions. These safeguards are fully compliant with the safety standards outlined above. The patented control system of these robots includes safety features customizable to the individual needs of the user. These features include, but are not limited to: position and velocity combined, TCP (Robot tool-center-point) position, tool orientation, speed and force, as well as momentum and power of the robot. Thanks to this, the cooperation of the robot and the human (operator) of the so-called HRC (Human-Robot Collaboration) is carried out in a safe manner, in accordance with applicable standards [www2].

When we look at collaborative robots, their construction is also well thought out. Rounded shapes, clearly rounded edges, and even properly designed transitions to minimize the occurrence of edges, all in order to eliminate the potential risk of injury to the operator. In the case of industrial robots, there is no need for such modifications due to the protective solutions used. These are not always physical protective barriers, as exemplified by the PILZ vision system.

Characteristics of a collaborative robot

By design, cobots should be very easy to program and have a high level of flexibility in their applications in industrial conditions. Graphical interfaces, cobot learning methods are significantly more accessible to less skilled operators. This does not mean that literally anyone can program. Ease of programming is the foundation of their flexibility in implementation – one day a CNC turning center (illustration 1 and 2), and the next an assembly line for small household appliances. The second foundation is the lack of the need for a solid foundation, because the weight of the cobots does not exceed 35 kg, which is very small compared to its older brothers, industrial robots. In the case of industrial robots, structures weighing more than 1 ton are not uncommon, which forces a strictly defined foundation of such a robot.

The low weight of collaborative robots is associated with a weaker payload, a shorter range, and meeting safety requirements also affects productivity. Remember that as the radius of action of the arm increases, its load capacity decreases. The maximum weight depends primarily on the construction of the robot and can be 16 kg, and the achieved travel speeds will not exceed 3 m/s. As a consequence, we are dealing with application limitations of collaborative robots – e.g. it is not possible to weld complex large-size structures or move objects with masses that require a force greater than human strength. Figures 5 and 6 show the different grippers used in the two different implementations.

Fig. 5. In the robotic machining station presented at the Abplanalp stand (STOM 2019), a robot cooperating with non-mechanical fastening of the transported object was used.

Fig. 6. Robot cooperating on a machining station with a mechanical workpiece gripper – Yamazaki Mazak STOM 2022 stand.

At the implementation stage, whether it is an industrial robot or a collaborative robot, it should be remembered that the maximum load capacity of the arm must take into account the mass of not only the moved object but also the gripper.

In this article, I presented two robotic CNC lathe machining centers. Why, with such CNC machines, a collaborative robot, despite some limitations, seems to be an “ideal” solution. Turning machining centers (Figure 7) are designed to allow access to the machining zone only from the front of the machine. Nowadays, regardless of the degree of automation, the operator must have access to the machining zone. The implementation of an industrial robot means serious difficulties in access to the machining zone, to the object, to tools, especially in the event of a failure or even KSO (catastrophic blunting of the blade). Then the intervention of the operator is necessary. The use of a cobot allows the simultaneous operation of the robot and the operator. Access to the machining zone may still be non-ergonomic, but it is still much better than when robotizing the station with the use of an industrial robot.

Fig. 7. An example of a turning and milling center – Nakamura Tome – stand of Abplanalp during international fair STOM 2019.

In 2019, about 5% of all robot implementations in industry were collaborative robots. Their percentage share is gradually increasing. Automation, including robotization, is a must. It results not only from the reasons for reducing the harmfulness of working conditions in which people work, but also from the shortage of qualified staff. In its assumptions, Industry 4.0 strives for fully automated factories in the full scope of the definition of what automation is.

Sources

1. Pawlak M., Automatyzacja procesów przemysłowych, “Prace Naukowe Instytutu Maszyn, Napędów i Pomiarów Elektrycznych Politechniki Wrocławskiej”, Nr 60, s. 1 2007
2. Gupta A. K., Industrial Automation and Robotics. Laxmi Publications (P) Ltd., University Science Press, s. 1., 2007
3. Kost G., Łebkowski P., Węsierski Ł.N., Automatyzacja i robotyzacja procesów produkcyjnych, PWE 2018

Sources www

1. Roboty współpracujące – zacznijmy od podstaw (2022.10.31)
2. Bezpieczna współpraca robota z człowiekiem (2022.10.31)
3. Cobot – czym różni się od standardowego robota przemysłowego (2022.10.31)