Design, Fabrication, and Performance Analysis of 2 (DoF) Model Gantry Hybrid Robot (Electric/Pneumatic) for Metallurgical Works

This paper presents the design, fabrication and analysis of two degrees of freedom (2DOF) model gantry hybrid robots. The hybrid robot
mechanism, comprising a series and parallel component, provides a vast range of workspace and accuracy. Pneumatic actuators are extensively utilized in industrial settings due to their low cost, compact size, high power-to-weight ratio, and reliability. However, the nonlinear dynamic characteristics of air compressibility and friction effects limit the precision of pneumatic actuators, reducing their time response and positional accuracy. Hybrid robots have various applications, including human-system interaction, medical robots, rehabilitation, and exoskeletons, among others. These applications necessitate robust precision and dynamic workspace computation as the two primary requirements.

Introduction

Nowadays, the usage of robots has become widespread in various industries and for factory automation purposes. A hybrid robot has been developed to assist human workers in heat treatment workshops and material handling tasks. The field of metallurgical work is particularly hazardous, and the work environment poses several risks. Workers and robots collaborate in the same workspace, which is why a hybrid robot must possess special characteristics such as high payload, safety, reliability, and a wide workspace [1]. A hybrid-type robot is capable of meeting these requirements due to its wide workspace, high payload capacity, and precision. The hybrid-type robot used in this study is composed of a stepper DC motor for horizontal load movement and a pneumatic actuator for vertical movement, as well as pneumatic gripper [2].

A pneumatic actuator offers the benefits of toughness, high payload-to-weight and payload-to-volume ratios, rapid speed and force capabilities, and a range of power transmission methods based on a straightforward operational mechanism [3], [4]. The metallurgical industry’s environment is unclean, hazardous, and varied. Consequently, a pneumatic actuator is suitable for a hybrid robot designed for metallurgical tasks. A compressed air actuator is a sturdy nonlinear system, and it requires a rational controller to overcome this nonlinear property. However, highly nonlinear dynamic features such as air compressibility and frictional effects, which combine with positional accuracy, are limiting factors that impede the use of compressed air actuators for accurate position control [5]. These nonlinear dynamic features make it difficult to regulate the pneumatic actuator. Several control algorithms have been proposed over the years to regulate the pneumatic actuator [6].

In this paper, a hybrid metallurgical model robot has been created to aid human laborers in heat treatment factories and material handling. The robot can lift and reposition bulky components and perform annealing, hardening, tempering, and component storage tasks. The work area’s furnace and storage area layout are depicted in Fig. 1.

Fig. 1. Working area for robot.

The model hybrid robot is shown in Fig. 2, using the stepper motor and pneumatic actuators.

Fig. 2. The model hybrid robot.

Mechanism Design and Analysis

The Design of the Structure by Using Influence Lines

Impact lines are an essential tool in the field of engineering design as they illustrate the version of a function (including the shear experienced in a structural member) at a specific point on a beam or truss due to a unit load situated at any point along its shape. Various significant characteristics analyzed by impact lines include reactions (the forces necessary for the structure’s supports to maintain static stability), shear, second, and deflection. These graphs play a crucial role in designing beams and trusses utilized in bridges, crane rails, conveyor belts, ground girders, and other structures where loads will traverse their span. By depicting where a load will have the greatest impact on any of the examined features, impact lines demonstrate the most critical points of load application.

The impact lines are both scalar and additive, which is why they are utilized even when the load being carried out is not a unit load or if there are multiple loads applied. To determine the impact of any non-unit load on a structure, the vertical results obtained by the impact line are multiplied by the value of the actual load to be applied. The entire impact line can be adjusted in scale, or just the highest and lowest results experienced along the line. The adjusted maximum and minimum are the crucial magnitudes that must be designed for in the beam or truss.

Concept of Influence Line

When designing a pillar or truss, it is crucial to plan for the scenarios that will cause the greatest expected responses, stresses, and moments within the structure in order to ensure that no part will fail during the lifespan of the structure. Dealing with dead loads (loads that do not move, such as the weight of the structure itself) is usually relatively simple since the loads are easy to predict and plan for. However, when it comes to live loads (any load that will be moved during the lifespan of the structure, such as people and furniture), it becomes much more difficult to anticipate where the loads will be or how concentrated or distributed they will be throughout the lifespan of the structure. Influence lines illustrate the response of a beam or truss as a unit load travels over it. The influence line allows designers to quickly determine where to place a live load in order to calculate the maximum resulting response for each of the following functions: response, stress, or moment. The designer can then scale the influence line by the highest expected load to calculate the maximum response of each function for which the pillar or truss must be designed. Influence lines can also be used to find the responses of other functions (such as deflection or axial force) to the applied unit load, but these uses of influence lines are less common.

Calculation of the Structure Design (Which Is [I] Section Steel Beam), Figs. 3 through 5 present that.

Fig. 3. The reactions effects.

Fig. 4. Diagram of reaction $(r_a)$ in the point b.

Fig. 5. The diagram of reaction $(r_b)$ in the point a.

By using effect of force, and taking the summation of moment at point B.

(1) $$\begin{array}{r}\sum Ma=0\end{array}$$

$r_a\times l=1\times (l-x)$ for F = 1 N

(2) $$\begin{array}{r}{r}_a=1-\frac{x}{l}\end{array}$$

By utilizing the effect of force and taking the summation of moment at point B:

(3) $$\begin{array}{r}\sum Ma=0\end{array}$$

$r_b\times l=x\times 1$ for F = 1 N

(4) $$\begin{array}{r}{r}_b=\frac{x}{l}\end{array}$$

(5) $$\begin{array}{r}M=\frac{X}{L}(l-a)\end{array}$$

At the point of the max effect:

$$\begin{array}{r}M=\frac{0.50}{1}(1-.5)\end{array}$$

By taking the force = 981 N or 10 kg

$$\begin{array}{r}{r}_{\text{a}max}=1-\frac{\text{x}}{\text{l}}\end{array}$$

$$\begin{array}{r}{r}_a=force\end{array}$$

By using the yield stress of 250 MPa

(6) $$\begin{array}{r}area=\frac{force}{pressure}=\frac{f_c}{p_c}\end{array}$$

$$\begin{array}{r}{f}_c=0.45\times f_y\end{array}$$

$$\begin{array}{r}{f}_c=0.45\times 250\end{array}$$

$$\begin{array}{r}{f}_c=112.5\end{array}$$

By adding the steel beam wight which is about 10 kg:

$$\begin{array}{r}area=\frac{force}{pressure}=\frac{196.2}{112.5}=1.744{\text{ mm}}^2\end{array}$$

Referring to the British code, the shape of steel beam is shown in Fig. 6.

Fig. 6. The dimensions of (I) section steel beam.

This represents the lowest value of the dimensions of steel beam in the code tables and it is also shown in the table.

The Horizontal (I) Section Steel Beam

By used the effect of moment and section modulus

(7) $$\begin{array}{r}S=\frac{moment}{force}=\frac{M}{f_b}\end{array}$$

$$\begin{array}{r}S=\frac{N\cdot m}{N}\end{array}$$

$$\begin{array}{r}{f}_b=0.6\times f_y\end{array}$$

$$\begin{array}{r}{f}_b=0.6\times 250\end{array}$$

$$\begin{array}{r}{f}_b=150m{m}^2\end{array}$$

$$\begin{array}{r}S=\frac{25}{150}\end{array}$$

$$\begin{array}{r}S=0.0017c{m}^2\end{array}$$

From the table of properties [8], and using the factor of area (S), we found that, the dimensions of the steel beam are: 102 × 44 × 7. They are the same dimension of the other steel beam; the length = 102, the width = 44, the thickness = 7, Fig. 7 shows the dimensions of the horizontal (I) section steel beam.

Fig. 7. The dimensions of the horizontal (I) section steel beam.

Both the dimension of the vertical and horizontal I section steel beam are very small because our load is not heavy totally. Fig. 8 shows the Kamer structure and the way of jointing.

Fig. 8. The kamer structure and the way of jointing.

Design of Pneumatic System

The pneumatic scheme consists of:

1. i)a pre-conditioning system (consisting of an air compressor, an FRL unit for filtration, regulation and controlled lubrication),
2. ii)pneumatic actuators,
3. iii)flow control and regulation valves and
4. iv)air conveying lines [7].

In view of the low volume air requirement, a 10 liter capacity air tank filled by a 1/2 HP electric motor compressor unit. An FRL is used for conditioning of the air.

A 30 mm stroke pneumatic actuator performs the vertical motion and a miniature air cylinder gripper unit is used for the gripper. Fig. 9, gives the pneumatic circuit used in the fabrication of the model robots.

Fig. 9. Pneumatic circuit for the hybrid robot.

Vertical Cylinder (Z) Design

Considering the mass of gripper with its cylinder operator is = 2 kg

F = 2 × 9.81 = 19.62 N

P = 4 bar, Efficiency = 96%

F = P × A × Eff.

$$\begin{array}{r}\text{A}=\frac{\text{F}}{\text{P}\times \text{Eff.}}=\frac{19.62}{4\text{y}\cdot {10}^5\times 0.96}=\frac{19.62}{384000}=\mathrm{0,00051}{\text{m}}^2\end{array}$$

$$\begin{array}{r}\text{A}=\frac{\pi {\text{D}}^2}{4};\text{D}=\sqrt{\frac{4\text{A}}{\pi }}=\sqrt{\frac{4\times \mathrm{0,00051}}{\pi }}\end{array}$$

D = 0,008056 m = 8.1 mm. Cylinder bore is selected as = 10 mm.

The vertical actuator is selected from manufacturer’s catalogue included later.

Design of the End-Effector

The best design of the basket, for general metallurgical operations as shown in Fig. 8, must be such that any oscillations present must be damped to prevent molten metal from spilling or causing accidents. But in heat treatment operations, since there is no molten metal, the damping requirements for basket are not severe. However, in view of the speed achieved by the long rodless cylinder (as seen in previous section), there will not be violent oscillation of the basket.

Since the basket is going inside a furnace where temperatures can reach as high as 900 °C (for hardening/tempering/annealing) the walls of the basket must be rigid and also that the gripper of basket must not stay in the furnace for a long time. In case, it is necessary to keep the gripper holding the basket for a long time, the gripper may be thermally insulated by providing proper insulation around the gripper.

The best gripper design that can be thought of is to provide a safety latch when the material is transported reaching the destination as shown in Fig. 10.

Fig. 10. The proposed design of end-effector with basket.

Gripper Cylinder Design

Assuming an efficiency = 96%

F = P × A × Eff.

$$\begin{array}{r}\text{A}=\frac{\text{F}}{\text{P}\times \text{Eff.}}=\frac{9.81}{4\text{y}\cdot {10}^5\times 0.96}=\frac{9.81}{384000}=\mathrm{0,0000255}\end{array}$$

$$\begin{array}{r}\text{A}=\frac{\pi {\text{D}}^2}{4};\text{D}=\sqrt{\frac{4\text{A}}{\pi }}=\sqrt{\frac{4\times \mathrm{0,0000255}}{\pi }}\end{array}$$

D = 0, 0057 mm = 5, 7 mm. Cylinder bore is selected as = 10 mm.

The gripper actuator is selected from manufacturer’s catalogue which is given later.

Sensor Selection

Inside the proposed robot, the sensors have the portion of: i) recognizing whether the actuator is at any set conclusion centers and, ii) sending hail to the PLC to proceed to the solenoid valves. Sensors are contraptions which can work both by infers of contact, e.g., compel switches, drive sensors, or without contact, e.g., light boundaries, talk about boundaries, infrared discoverers, ultrasonic intelligent sensors, other smart sensors.

Proximity Sensors

Proximity Sensors are sensors which identify whether or not the object is in a specific spot. These sensors are known as proximity sensors Fig. 11. These sensors say either “yes” or “no” depending on whether or not the object is in a certain place, to be characterized, has been taken up by the protest. These sensors [8], which indicate two statuses are also known as parallel sensors or in uncommon cases as initiators. Extra sensors utilized are small scale switches, restrain switches or restrain valves. Since developments are identified by implies of contact detecting within the last mentioned sort, important useful necessities must be satisfied by these sensors. Similarly, these constituents are prone to deterioration. On the other hand, electronic proximity sensors operate without physical touch. The advantages of non-contact proximity sensors include:

Fig. 11. Inductive proximity sensors.

1. a)Precise and automated detection of spatial positions,
2. b)Non-contact detection of objects and shapes; electronic proximity sensors do not require any physical contact between the sensor and the workpiece,
3. c)Rapid switching characteristics; as the output signals are generated electronically, the sensors are free of bounce and do not produce error pulses.
4. d)Durable functionality; electronic sensors do not contain any moving parts that may wear out,
5. e)Limitless number of switching cycles,
6. f)Cost-effective versions are also available for use in hazardous environment,
7. g)A lessening in downtime of apparatus can moreover be accomplished by implies of sensors, since collapse is rapidly recognized and signaled.

Reed Proximity Sensor

Proximity sensors that are magnetically activated detect the attractive zones of permanent magnets and electromagnets. In the case of a reed sensor, the contact edges are composed of ferromagnetic material (Fe-Ni alloy, where Fe stands for iron and Ni for nickel) and are placed inside a small glass tube. This tube is then filled with an inert gas such as nitrogen (an inert gas is one that is non-reactive and non-flammable). Fig. 12 illustrates a few instances of magnetic reed switches.

Fig. 12. The magnetic proximity sensor (reed switches).

Stepper Motor and Controller Selection

The gantry robot can have a wide range of work envelopes. In laying out the application work area, the work envelopes are made larger, speed must be reduced and final acceleration/deceleration distance between end points may have to be shortened. These factors become critical when handling very heavy payloads.

Gantry robots allow the capability of one robot to do the work of many floor-mounted pedestal robots, as discussed earlier the layout of what interacts with the gantry robot becomes more of a consideration, and in many cases is easier to implement and allows more efficient utilizing of resources.

Final Specifications

Based on the above criteria and condition of operation, the specifications of the proposed robot for metallurgical heat treatment operations are as given in Table I.

Table I. The Specifications of Robot for Metallurgical Heat Treatment Operations

Serial No.	Parameter	Value
1.	Robot configuration	Gantry
2.	Robot type	Cartesian
3.	Work area	16,000 × 5,000 mm
4.	Degrees of freedom	2
5.	Pay load(with parts loaded in a basket having a non-hinged lifter)	100 kg
6.	Accuracy	± 5 mm
7.	Powering	Electric/Pneumatic
8.	Gripper	Pneumatic with steel line
Model pneumatic robots
1	Scale of the model robot	1:32
2	Actuators: Electric	500 mm for longitudinal
	pneumatic	Movement
		30 mm for vertical
		25 mm for gripper
3	Pay load	2 kg
4	Accuracy	± 1 mm

Performance Analysis

The measured values of position and velocity obtained from computer simulation program are compared with those obtained through measurements and found to correlate fairly well. The discrepancies in results between simulation and performance are due to friction, which is not truly accounted in the simulation process.

Fig. 13 shows variation of linear speed of vertical cylinder for picking up the bucket, and Fig. 14 shows variation of linear speed of gripper cylinder for opening and closing the gripper.

Fig. 13. The variation of linear speed of vertical cylinder with time in pressure 5 bar.

Fig. 14. The variation of linear speed of gripper cylinder with time in pressure 5 bar.

Conclusions

A two-dimensional hybrid robot is developed initially which can be extended later into a full-fledged robot for use in a metallurgical application. The overall behavior of the simulation closely resembles that of the actual system. This design based on a two degrees of freedom kinematic scheme, can perform basic tasks like heat treatment, material handling, and some tasks with enough precision for industrial applications. Future researches should address the improvement of control strategy, mainly for pneumatic actuators.