Substantiation of Parameters of Friction Elements of Bernoulli Grippers With a Cylindrical Nozzle

Introduction

During implementation of the modern automation equipment of handling operations using industrial robots use different types of grippers (Chan, et al. 2001; Ceccarelli, 2004; Shameli et al., 2007; Henrich, Wörn, 2012; Fantoni et al. 2014a; Fantoni et al., 2014b). In addition, devices that use the power effect of a jet of air coming from a nozzle (Li, Kagawa 2013; Ozcelik et al., 2003; Savkiv et al., 2017a; Savkiv et al., 2019a; Festo AG & Co, 2020; SMC, 2020; Aventics, 2020; Schmalz, 2020). The nature of the interaction of the air jet with the load depends on many parameters, which allows you to use the positive effects of this interaction for various tasks: to hold loads due to aerodynamic attraction; contactless transportation of loads on air cushion; use reactive and viscous friction force to orient transportation objects. The combination of these interaction effects allows you to create fundamentally new devices for contactless capture, orientation and transportation of production facilities.

Currently, jet gripping devices using the aerodynamic attraction effect (Bernoulli effect) are most widespread, so usually these grippers are called Bernoulli gripping devices (BGD). Through the practical value of capturing Bernoulli, researchers continue to work to optimize the design of invaders of this type. The very first mention of the Bernoulli clamp study was presented by Welanetz, & Syosset (1956). In their article, they illustrated the mechanism by which Bernoulli's grip creates a vacuum and attraction force. Later, researchers installed rubber pads on the lower part of the grip to fix the height of the gap between the delight and the workpiece. Thus, the friction force caused by the contact between the rubber pads and the workpiece prevented the manipulation object from sliding or falling during horizontal movement (Brun, & Melkote, 2009). Giesen et al. (2013) and Brun, & Melkote (2009) used Bernoulli gripping devices to lift and transport objects, such as solar panels. In addition, Li, & Kagawa (2014) designed a Bernoulli-based device that could capture a silicon plate contactlessly.

One of the main differences between the Bernoulli grippers and the traditional rubber vacuum cup is that the Bernoulli gripper releases air to the outside, creating a vacuum, and this air discharge prevents outside air from flowing through the vacuum region to the inside perimeter of the object. Therefore, even if the surface of the preform is very rough, the Bernoulli grip can maintain a vacuum. This allows Bernoulli grippers not only to attract smooth objects, but also rough and irregular shapes, such as tissue, soft and coarse skin (Ozcelik, Erzincanli, 2002; Dini et al., 2004), and food products such as meat, tomatoes, bread and others (Erzincanli et al., 1998; Davis et al., 2008; Petterson et al., 2010). Now BGD are widely used in the radio-electronic industry for manipulation of semiconductor plates, solar elements and printed circuit boards (Stühm et al., 2014; Savkiv et al., 2019b). Application of BGD in polygraphy at production and the subsequent use of lithographic printing forms (McIlwraith, Christie, 2003).

Previous studies of Bernoulli grippers have focussed on its steady state suction force. Shi, & Li, (2018) study experimentally and theoretically investigates the dynamic characteristics of the Bernoulli gripper. In practical applications, the gripped workpiece is lifted by placing the gripper immediately above the workpiece and then supplying compressed air to the gripper. In our pick-up experiment, the workpiece started to oscillate vertically after lifting, and then, the oscillation amplitude decreased until the workpiece became stable. Based on this experimental observation, we propose a mass-spring-damper model in which the steady state suction force is considered a spring and the squeeze-film flow exerts an additional damping force.