The computer – assisted design of the R.I. 01 industrial robot used for loading the BB-01 flexibile line utilized to cut revolution parts

THE COMPUTER - ASSISTED DESIGN OF THE R.I. 01 INDUSTRIAL ROBOT USED FOR LOADING THE BB-01 FLEXIBILE LINE UTILIZED TO CUT REVOLUTION PARTS

D.G. Zisopol

Petroleum - Gas University of Ploiesti;

Snamprogetti Romвnia

Introduction

The machine building field uses industrial robots widely due to their high features related to use and operation and proved by productiveness, high precision, fiability and efficiency.

Taking into account the above-specified circumstances, this paper shows the results having been gained in connection with the computer-assisted design of the R.I. 01 industrial robot. The said robot is a mobile “Pick and Place” - type one, being suspended, flexiblely programmed and used for loading cylindrical semi-finished products of various types and sizes on the automatic lathes of the BB-01 flexible line.

The BB-01 flexible line includes six working stations serviced by three R.I. 01 manoeuvring robots and equipped with machine tools controlled by means of a process computer (three working stations have SBB-01 lathes while the remaining ones have RBB01 grinding machines).

See Fig. 1: it shows how the R.I. 01 industrial robot is integrated into the working system of the BB-01 Flexible Line.

Fig. 1. Integration of the R.I. 01 industrial robot into the working system of the BB-01 flexible line

R.I. 01 Loading Robot

The computer-assisted design of the R.I. 01 industrial robot uses techniques of interactive graphics used in conjunction with the design of components, parts and assemblies belonging to some various types of electronic, electromechanical, electric and mechanical equipment.

The development of the mechanical structure specific to the R.I. 01 industrial robot takes into consideration the following aspects:

the geometric configuration of the parts to be handled, machined or controlled;

the type and the degree of automation specific to the machine tools to be utilized;

the technological film of the parts having been taken into consideration;

the necessity requiring the machine tools to be grouped in compliance with a special spatial configuration permitting the use of the industrial robots in conjunction with the control and handling operations;

the necessity of managing and controlling all working systems of the BB-01 flexible line unitarily.

The step related to the design of the geometric models elaborated by means of the AutoCAD 2002 program is followed by the next one, which consists in simulating the operation of the R.I. 01 industrial robot. The said simulation is performed due to use of the 3D Studio Max program, which interpolates the trajectory of the resulting motion depending on several parameters, its action of interpolating being possible due to the prior supply of information regarding the initial and final condition of the mechanical articulated structure specific to the element being analyzed.

The immediate result of such an approach is the elimination of the overlaps between the working spaces of the industrial robot and the same spaces existing among the components of the BB-01 Flexible Line.

The 3D Studio Max program provides a multimedia support necessary to an easy understanding of the operational part specific to the R.I. 01 industrial robot components and the information related to the dynamics of the whole system.

See Fig. 2 for the type and the dimensions specific to the R.I. 01 loading robot.

Determining the position of the characteristic point assimilated to the last element of the loading robot requires a local system of co-ordinates (xOy) to be generated (see Fig. 3).

Fig. 2. The R.I. 01 loading robot sketch

See the Table 1 for the operational and design features of the R.I. 01 loading robot.

Table 1 - Operational and design features of the R.I. 01 loading robot

Fig. 4. - The central spindle of the system

The R.I. 01 robot works for:

loading the NC lathes belonging to the machining system of the BB-01 flexible line;

modifying the position of the part machined through the same machines.

The BB-01 flexible line uses three R.I. 01-type robots servicing the three lathes of the machining system. The three arms of the robot raise the start semi-finished product from a feeder system and take it to the loading position specific to the each lathe. Whenever the sensor system of the lathe shows that the semi-finished product is adequately caught by the lathe chuck, the fingers of the loading robot relieve the part and the whole arm moves to reach the neutral position. The loading robot can modify the part position whenever the said part may not be machined within a single positioning. The part is raised under safety plane conditions and then rotated at 1800; after that, the lathe is loaded again and the arm goes back to reach the neutral position.

The information below describes the operational and design features of the components constituting the R.I. 01 loading robot.

The central spindle of the system (see Fig. 4) is a variable-section cylinder whose base centre is in the origin point of the total system of co-ordinates; it sustains the part transfer subsystem inside the BB-01 flexible line and the horizontal frame of the loading robot.

The bottom accommodates the operating motor of the transfer robot holder as well as the power lines and the main lines of data afferent to all working robots of the BB-01 flexible line; the said components are located inside the central spindle.

The horizontal frame (Ci; i = 1…3) holding the arm loading robot is a I - section bar representing the support of the translation motion afferent to the robot arm, so that the terminal element can reach the working positions as required (see Fig. 5).

An electrically - operated leader screw makes the translation motion of the loading robot be possible, its electric motor being located above the central spindle of the system. The three horizontal frames (see Fig. 3) are dephased at 1200 and sustained as follows: one end through the central spindle of the system and the other end through three vertical columns. The bottom of the horizontal frame accommodates the power lines supplying electric power to the electric motors of the loading robot as well as the main lines of data afferent to the leading system of the flexible line.

Fig. 5. The horizontal frame holding the arm of the loading robot

The arm (Blnc i ; i = 1…3) of the loading robot is a parallelepiped guiding the robot (see Fig. 6). The translation zone (1) of the loading arm is also a parallelepiped and represents the base of the robot. The inside of the translation zone accommodates the supplying socles of the downstream electric motors (the power lines) as well as the socles of the main data lines (the main line for operation and the sensory main line).

Whenever the rotary motion of the leader screw (inside the horizontal frame) is transformed into a translation one, a rack existing inside the conjugate I - shape zone (see Fig. 6) makes the arm of the loading robot move vertically. The MRInc1 electric motor operates all three arms simultaneously (in the local plane xOy) through an assembly of bevel gears whose axes are perpendicular. The front faces of the translation zone include: position sensors (SRInc2i; i = 1…3) and contact sensors (SRInc3i; i = 1…3), which give information about the working position of the displacement speed and the step when the arm travel limits are reached. The inside of the holding zone 2 has racks along all useful length (on two opposite faces) and represents the arm translating support. Two millimeter grids parallel to the two racks provide a measurement support to the position sensor of the forarm. There is no operating element inside this segment, the space covering the cable pieces of the power line and the main lines of data.

Fig. 6. The arm of the R.I. 01 loading robot

The forarm (AbInc i; i = 1…3) is a parallelepiped-shape structure, whose inside includes:

an operating motor (MRInc2i; i = 1…3), which permits the forarm to perform the translation motion vertically along the axis y;

a motor (MRInc3i; i = 1…3), which rotates the hand of the arm around the same axis (see Fig. 3). An assembly consisting of a rack and a gear transforms the rotary motion of the MRInc2 motor shaft into a translation motion, so that the loading forarm can move vertically along the axis y.

The lower end of the loading forarm has a rotary coupling (see Fig. 7), consisting of a radial and axial bearing, which takes over both the radial loadings generated by the part motion and the axial ones determined by the weight of the hand and the part being rotated, respectively.

Fig. 7. The forarm and the hand of the R.I. 01 loading robot

A spindle operated by the MRInc3 motor connects the forarm with the hand of the loading robot.

The sensors equipping the forarm of the R.I. 01 loading robot are the following:

the position sensor (SRInc4i; i = 1…3), giving information about the displacement of the forarm in the vertical plane y;

the speed sensor (SRInc5i; i = 1...3), giving information about the displacement speed of the forarm;

the rotation sensor (SRInc6i; i = 1…3), giving information about the angle of rotation afferent to the robot hand whenever the position of the part machined within the working system gets modified;

the load sensor (SRInc7i; i = 1…3), which gives information about the useful load to be handled;

the contact sensors (SRInc8i, SRInc9i; i = 1…3), which give information about the presence of the forarm at the extremity points of the translation travel.

The parallelepiped-shape hand of the R.I. 01 loading robot has three cells (see Fig. 7) at its bottom, the said cells being capable to accommodate the working fingers. A MRInc4i electric motor ( i = 1…3) operates the fingers through a lever system, which helps with keeping the fingers tight and separate whenever the semi-finished products are handled. The hand has a single degree of freedom - one rotation around the axis y - and keeps a fix position as against the forarm of the robot. The sensors equipping the hand of the loading robot give information about:

the moment of the tightening forces applied to the semi-finished products (SRInc10i - moment sensor, where i = 1…3);

the presence of the fingers at the extreme positions (SRInc11i - contact sensor, where i = 1…3).

The four fingers of the R.I. 01 loading robot hand are characterized by the following: manufacture material: steel; a special shape, which makes parts of diameters ranging between 20 and 100 mm be caught; aluminum alloy jaws avoiding any damage of the surfaces whenever the fingers work.

See Fig. 8 to notice the type and the dimensions of the R.I. 01 loading robot finger.

Fig. 8 - The type and the dimensions of the R.I. 01loading robot finger

Using the same type of fingers for parts of various diameters requires the distance “x” (see above) of the fingers (Fig. 9).

The values of that distance “x” as calculated for each type and size regarding the parts to be handled are covered by the data stock afferent to the operating program of the R.I. 01 loading robot.

Fig. 9 - The distance “x” permitting the R.I. 01 loading robot fingers to be kept tight

The displacements of the diverse components belonging to the loading robot are modified on-line depending on the above-specified data stock; so, the semi-finished products can be precisely positioned within the lathe chuck.

Сonclusions

The authors of this paper used the computer-assisted design method and tried to describe the main characteristics of the R.I. 01 industrial robot, namely its type and dimensions as well as its operational and design characteristics. The industrial robot having been described is a mobile equipment (“Pick and Place” type) suspended, flexiblely programmed, electrically operated and used for loading cylindrical semi-finished products on the automatic lathes equipping the BB01 flexible line.

This paper covers the results of a prodigious research activity related to the computer-assisted design of the R.I. 01 industrial robot used for loading cylindrical semi-finished products on the automatic lathes of the BB-01 flexible line utilized to cut revolution parts.

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