Maja Čavić

Optimal synthesis of the worm-lever mechanism for humanoid robots shrug

Emotions represent a significant means of nonverbal communication and their expression represents an important aspect of social robots functionality. There are two basic ways of expressing emotions. The first one is based on facial expressions that can be realized by moving a particular part of face or by displaying a picture on the screen that represents a face with characteristic features such as eyebrows, eyes, nose and mouth. Combining them is also possible. The second way of nonverbal communication is based on gestures, especially using arms. This paper presents an optimal synthesis of shrug mechanism for humanoid robots. Based on the set requirements the worm-lever mechanism is proposed. It has 1 DOF and enables simultaneous shrug of both shoulders. It consists of a worm which is meshed with two worm gears having different directions of rotation and two four-bar lever mechanisms whose input links are rigidly connected to the worm gears. Based on the kinematic-dynamic analysis the dynamic model is formed, the objective function is defined, the constraints are prescribed and the optimal synthesis is performed. The maximum torque on the input link of the lever mechanism, the driving torque of the complete worm-lever mechanism, the range of transmission angle and the rotation range of the worm gears are determined. The lever mechanism has high efficiency in all positions because the transmission angle has a high value during the whole movement. The worm mechanism enables a significant reduction of driving torque and has acceptable efficiency. The rotation range of the worm gear is small – the mechanism movement is very quick and therefore the shrug speed is large, which was the basic requirement for realization.

Drive System of the Robot Eyeballs and Eyelids with 8 DOFs

Significant aspect of the socially interactive robots are eyes which present the most expressive part of the face, especially when it is rigid as is the case with majority of the robots. For this reason to the design and realization of the eyes a particular attention should be dedicated. This paper presents the drive system of the robot eyeballs and eyelids with 8 DOFs. Eyeballs drive system has 4 DOFs and consists of two symmetrical planar mechanisms that enable independent motion of the eyeballs about the yaw axis—abduction/adduction movements and two identical spatial mechanisms that enable independent motion of the eyeballs about the pitch axis—elevation/depression movements. Eyelids drive system has 4 DOFs and consists of four structurally equal spatial mechanisms that enable independent motion of each eyelid—mechanisms for driving the upper and lower eyelids, respectively, are symmetrical. Based on the kinematic analysis, motion simulation of eyeball and upper/lower eyelid is performed. Velocities of the eyeball/eyelids movements are within the parameters of the human eye. The structure of the eyeballs drive system is such that enables inserting the camera directly into the eyeballs. In this way it is possible to achieve some of the functions of robots artificial vision such as recognizing objects, distance estimation etc.

Robotic Eyes with 7 DOFs: Structural Design and Motion Simulation

The paper presents the structural design and motion simulation of the robotic eyes with the characteristics of the female eye. The eyeballs/eyelids drive system with total 7 DOFs is proposed. The eyeballs drive system has 3 DOFs and enables the rotation of both eyeballs together around the pitch axis and their independent rotation around the yaw axis. The proposed solution enables the installation of cameras directly into the eyeballs. Also, it is possible to independently rotate the upper/lower eyelids of each eye, where the eyelids, in relation to the eyeballs, are rotated in two planes. Motion simulation of eyeball and upper/lower eyelids is performed. For the range of the motion that corresponds to the human eye, the angular velocities of the eyeball and upper/lower eyelids reach and exceed the kinematic parameters of the human eye.

Increasing the Resistance of Scuffing for HCR External Helical Gearing

The paper analyses the way to increase the resistance of HCR external involute gearing from a scuffing point of view. The scuffing is the most important damage of teeth flanks of HCR involute gears. In the case of warm scuffing; it is the combined action of high pressure between surfaces, high sliding speeds, and excessive contact temperature, resulting from pressure and sliding speed values, which cause oil film rupture between the teeth flanks. Adopting suitable geometry of the tooth curve profile, it will be defined certain values addendum heights for meshing wheel according to criteria of specific slips and corrected head shape of the teeth of both wheels. The paper deals with assessment and theoretical analysis of the impact of the HCR tooth profile resistance to scuffing on the basis of integral temperature criterion according to Winter-Michaelis criterion, researching especially two factors: factor of load distribution (Xe) and factor of gear geometry (XG).

Kinematic-Dynamic Analysis of the Cam-Worm Mechanism for Humanoid Robots Shrug

Having in mind that humans use non-verbal communication extensively is very important to enable social robots with this capacity. There are two basic ways how it can be expressed. First one is by facial expressions by appropriate moving face parts, like eyebrows, eyeballs, eyelids, lips, either as manufactured real parts or by presenting them on screen—combining them is also possible. The second way of non-verbal communication is by gestures. This paper presents the kinematic-dynamic analysis of shrug mechanism for humanoid robots. Based on the set requirements, the cam-worm mechanism that has 1 DOF and enables the simultaneous shrug of both shoulders is proposed. It consists of a worm which is meshed with two worm gears whose directions of rotation are opposite and the two cam mechanisms whose input links—cams, are rigidly attached to the worm gears. Within the kinematic-dynamic analysis, the cam profile and the worm parameters are defined and the torque on the cam/worm gear and the driving torque of the complete cam-worm mechanism are determined. The cam mechanism has a high efficiency in all positions because the values of the pressure angle are within the prescribed ones during the entire movement. Worm mechanism enables a significant reduction of the driving torque and has acceptable efficiency. The rotation range of worm gear/cam is small and the movement of mechanism is very fast wherefore the shrug speed is large, which was one of the main requirement for realization.

Optimization of HCR Gearing Geometry from a Scuffing Point of View

The paper deals with an issue of increasing the resistance of HCR external involute gearing from a scuffing point of view. It reports on a difference between involute gears with low contact ratio (LCR) and those with high contact ratio (HCR). The paper describes scuffing as the most significant damage done to the teeth flanks of HCR involute gears. In the case of warm scuffing, it is the combined action of high pressure between surfaces, high sliding speeds, and excessive contact temperature, resulting from pressure and sliding speed values, which consequently cause oil film rupture between the teeth flanks. Adopting a suitable geometry of the tooth curve profile, certain values of addendum heights for the meshing wheel will be defined according to the criteria of specific slips and corrected head shapes of the teeth of both wheels. The paper deals with the assessment and theoretical analysis of the impact of the HCR tooth profile resistance to scuffing on the basis of integral temperature criterion according to the Winter-Michaelis criterion. The basic relations for assessing the scuffing properties of an HCR involute gearing profile are derived, as well as the optimization of geometrical parameters of HCR gearing based on theoretical considerations on the properties of HCR gearing in terms of its resistance to warm scuffing combined with geometrical constraints against interferences. Finally, the results of the obtained optimization are compared with experimental results provided in previous research. A significant benefit in a theoretical area is the generalization of the integral temperature criterion for involute HCR gearing. By optimizing the criterion for the integral temperature of involute HCR gearing, the minimal flash temperature is obtained and the condition for the occurrence of scuffing is minimized.

Social Humanoid Robot SARA: Development and Realization of the Shrug Mechanism

One of the basic requirements of socially interactive robots is that they are able to effectively communicate, verbally and non-verbally. In addition to communication via speech, non-verbal communication of the robot is of utmost importance enabling different informations to be communicated in a simple and intuitive manner as well as expressing emotions. The paper presents the development and realization of the shrug mechanism as an addition to the assortment of non-verbal communication of socially interactive robots. The realized shrug mechanism has 1 DOF and enables lifting/lowering both shoulders together. It consists of a ballscrew shaft/nut mechanism that is coupled with a six-link planar lever mechanism. Within the kinematic-dynamic analysis, the basic parameters of the lever mechanism are defined – driving force on the input link, the vertical stroke of the end point of the shoulder and the dynamic efficiency of the lever mechanism. By optimal synthesis the driving force on the input link is reduced and, at the same time, the stroke of the input link is the smallest, while the stroke of the output links is the largest. That is why the movement of shoulders shrug is fast and short-termed, which was the basic requirement for realization of a movement that largely resembles to human-like movement. In addition, the mechanism is efficient in all positions during motion because the values of the transmission angle are within the prescribed values for the lever mechanisms. Ballscrew shaft/nut mechanism, besides enabling additional torque reduction, is also low backlash which is significant for motion control. The realized shrug mechanism enables high speed of shoulder shrug for small driving torque, has low backlash and high efficiency, compact design and small mass and dimensions.

Influence of the Teeth Number on the Gear Module Value and Load Capacity of Gear Pair in Universal Helical Gear Drives

The basic parameters of the universal gear drives, except the axis height, are not defined by the standard, so the manufacturers of universal gear reducers can define them in their way. Most of the manufacturers followed the parameter values of universal gear reducers of leading world producers in order to ensure their interchangeability and the better positioning of their gear units at the market. This paper deals with the analysis of the influence of the gear pair teeth number on the size of the module, as well as on the load carrying capacity of single-stage universal gear units. For defined gear ratio values, different combinations of teeth number of pinion and driven gear were selected. Further, it was made calculation of the basic geometric dimensions of the gear pair, as well as the load capacity. ARTICLE HISTORY Received 10.01.2018 Accepted 28.02.2018 Available 15.03.2018

Reducing of Scuffing Phenomenon at HCR Spur Gearing

The article deals with possibility of increasing the resistance of HCR spur gearing from a scuffing point of view. Scuffing is the process that occurs when the surfaces of two contacting bodies are joined by localized welding and then pulled apart. A material transfer occurs between the two contacting surfaces due to high metal-to-metal contact and hence produces a weld. Since there are great pressures between teeth flanks and the load is higher, the scuffing is the most important damage of teeth flanks of HCR involute gears. The scuffing traces appear in the form of streaks or scratches with rough bottoms and sides, often appearing as bands of variable depth width oriented in the direction of the height of the tooth, and affect isolated zones or their whole width. In the case of warm scuffing; the combination of high pressure exists between teeth surfaces, high sliding speeds, and excessive contact temperature, resulting from pressure and sliding speed values, which cause oil film rupture between the teeth flanks. HCR profiles are more complicated than standard involute profiles, they have greater predisposition for occurring interference, pointed tip thickness, but also undercut of teeth during the production (primary production interference). Due to increased addendum height, there is larger possibility of occurring some interference or pointed tooth tip. Therefore it should prevent these errors and check if all equation and constraints are satisfied. This paper describes finding optimal solutions for geometry of the tooth curve profile. It will be defined certain values addendum heights for meshing wheel according to criteria of specific slips and corrected head shape of the teeth of both wheels. In the same time, this optimization is joined with assessment and theoretical analysis of the impact of the HCR tooth profile resistance to scuffing on the basis of integral temperature criterion according to Winter-Michaelis criterion. A significant benefit in a theoretical area is generalization of the integral temperature criterion for involute HCR gearing.

Dynamic Optimization of the Cam-Lever Mechanism for Thermoforming Machine Tool Driving

Considering that the most important use of thermoforming is in the production of plastic packaging for the food and pharmaceutical industry, it is essential that formed products remain sterile through the entire thermoforming process. Most machines used for thermoforming have a tool holder with one degree of freedom—DOF, which allows only vertical motion of the tool. After the thermoforming process, the formed products are ejected from the tool with compressed air, which may cause contamination and/or deformation of the products. We propose a working mechanism for driving the tool, which, compared to conventional machines, guarantees both a shorter working cycle and sterility of the formed products during the entire process. Products are punched out after forming and accepted and transported with an adequate mechanism to the manipulation module, where they are sorted and packed. This paper presents a dynamic optimization of the thermoforming machine working mechanism with 2 DOFs which consists of two cam-lever mechanisms that enable translation, rotation and complex motion of the tool. Based on the set of technical requirements, kinematic synthesis of the cam-lever mechanism is performed. SVAJ diagrams for the cams and the dimensions of the lever mechanism links are defined. Based on the kinetostatic analysis, a dynamic model of the cam-lever mechanism is formed and the driving torque for both lifting and rotation of the tool is determined. The optimization problem is formed and the objective function is defined as the minimization of the required driving torque. Based on the set constrains, a dynamic optimization is performed using the method of genetic algorithm. By comparing the results before and after optimization, it is concluded that the driving torque is lower by 50.3%.