STUDY, DESIGN AND CONTROL ROBOT PALLETIZER NGHIÊN cứu, THIẾT kế và điều KHIỂN ROBOT gắp HÀNG

STUDY, DESIGN AND CONTROL ROBOT PALLETIZER NGHIÊN CỨU, THIẾT KẾ VÀ ĐIỀU KHIỂN ROBOT GẮP HÀNG a {vanlinhkh, buiquangvinh1712, babentanh}@gmail.com b {21000883, cbpham}@hcmut.edu.vn, c

STUDY, DESIGN AND CONTROL ROBOT PALLETIZER

NGHIÊN CỨU, THIẾT KẾ VÀ ĐIỀU KHIỂN ROBOT GẮP HÀNG

a {vanlinhkh, buiquangvinh1712, babentanh}@gmail.com

b {21000883, cbpham}@hcmut.edu.vn, c dungcva@ hcmut.edu.vn

ABSTRACT

Industrial robots are being utilized in many applications due to their stable operation, high flexibility and precision This paper presents a type of robot that is useful in applications

of loading and unloading The robot has 4 degrees of freedom and is structured in such a way that actuations in horizontal motion and in vertical motion are decoupled In this paper, a complete process to design a robot palletizer is highlighted, including conceptual design, mechanical and electrical design, prototype implementation and accuracy evaluation

Keywords: industrial robot, palletizer, mechatronic system

TÓM TẮT

Robot công nghiệp hiện đang được ứng dụng trong nhiều lĩnh vực khác nhau nhờ vào tính ổn định, khả năng thích ứng linh hoạt và tính chính xác trong vận hành Bài báo này giới thiệu về một loại robot được sử dụng phổ biến trong các ứng dụng xếp dỡ Robot có 4 bậc tự

do, có cấu trúc dẫn động được tách riêng theo phương chuyển động ngang và chuyển động thẳng đứng Trong bài báo này, nhóm tác giả xin giới thiệu một quy trình hoàn chỉnh để thiết

kế một robot gắp hàng, bao gồm cả thiết kế ý tưởng, phần cơ điện tử, chế tạo nguyên mẫu và đánh giá chính xác

Từ khóa: robot công nghiệp, robot gắp hàng, hệ thống cơ điện tử

1 INTRODUCTION

Thanks to the development of technology, the robot was invented to release humans from performing of heavy, dangerous and toxic works The most common applications of robots in industry can be listed as spraying paint, welding, assembly, etc

Today, many domestic companies have also been using robots for production jobs as assembly, welding, However, in loading and unloading stages as shown in Fig 1a, manual handling have been still found quite common These heavy works would have bad effect on the health of workers Therefore, proposing a robot that can be used in automated loading and unloading systems as illustrated in Fig 1b is necessary

Most types of robots in the current market are designed from revolute joints In this paper, the robot structure has 4 degrees of freedom (DOF), including 2 revolute joints and 2 prismatic joints The links were jointed and formed parallelograms of moving rules The paper

is organized as follows: a conceptual design of 4-DOF robot is presented in section 2 This is followed by kinematic analysis in section 3 Mechanical design and electrical design are addressed in section 4 and section 5, respectively Simulation results to verify the kinematic analysis are validated in section 6 Experimental results to evaluate accuracy are discussed in section 7 Finally, section 8 concludes the paper

a) b)

Figure 1 Loading, unloading crafts and by robot [1]

2 CONCEPTUAL DESIGN

To perform loading and unloading tasks, the robot structure must have abilities to:

then arrange them onto pallets as illustrated in Fig 2

layers or in a pillow under the circle, as illustrated in Fig 3

conveyors

Pallets

end-effector products

Figure 2 Picking up product from conveyors onto pallets

Figure 3 Typical arrangement of products on pallet [2]

With the given requirements, the robot mechanism must have at least 4 DOFs and is constrained in such a way that the axis of the end-effector is always kept in the vertical direction as shown in Fig 4 In this mechanism, 3 parallelograms can be observed such as AKLB, AHGB, and BFEC

E

P

φ 2

dc

N

L

B

F G

o

K

I

A H

φ1

M

l z

l x

Figure 4 4-DOF mechanism for robot palletizers

To simplify the kinematic analysis, link lengths are designed under the constraint in Eqn (1)

𝐼𝐾

where a is a constant

Combining the parallelogram structures and the constraint in Eqn (1), then point C will always in line through A and I, and satisfies Eqn (2)

𝐴𝐼

3 KINEMATIC ANALYSIS

Kinematic analysis of robots is to establish the relation between the joint angles / offsets

3.1 Forward kinematic

φ 1

l 1

Y 0

X0

ZQ

Y Q

X Q {Q}

Figure 5 Assigned frames to locate point P

As discussed in section 2, the position of the end-effector (x, y, z) is only affected by

Fig 5, together with Eqn (2), the position of the end-effector P can be derived:

{

𝑥 0

𝑦

0

𝑧 0

(3)

Fig 6 shows a simplified schematic diagram of the robot so that the orientation of frame {2} which is attached to the end-effector can be described relatively to frame {0} as follows:

X 1

X 2

P

φ2

φ1 O

Z 0

{0}

{1}

Y 1

Z 2

{2}

Y 2

Figure 6 Assigned frames to orientate the end-effector

3.2 Inverse kinematic

By combining Eqns (3) and (4), the solution of the inverse kinematic is determined as follows:

{

𝑎

𝑥𝑃

(5)

It is noted that the solution in Eqn (5) is solvable, however it is only valid when the geometrical constraint in Eqn (6) is satisfied

4 MECHANICAL DESIGN

This section employs the theoretical basis in section 2 and the results of kinematic analysis in section 3 to design link lengths of the robot palletizer that encloses a given workspace as illustrated in Fig 7 With this desired workspace, link lengths are calculated and shown in Table 1

Table 1: Link lengths of the robot palletizer

o

L

K

I

A H

B

E F

G

P

l x

l z

l 1

400

850

Figure 7 Illustration of robot workspace

Figure 8 3D CAD model of robot palletizer

Based on data in Table 1, a 3D CAD model of the robot palletizer is designed in SolidWorks as illustrated in Fig 8 Then, a prototype of the robot palletizer is fabricated as demonstrated in Fig 9

Figure 9 Prototype of the robot palletizer

5 ELECTRICAL DESIGN

5.1 Actuators

In order to drive the robot, 2 DC servo motors, with DCS810 drivers, are employed to

VCC GND EA+

NC E+5V

EGND Motor + DC Servo

DCS810 Driver

EB+

EB-24VDC

Ch-A Ch-B VCC Gnd

Motor

VCC GND A+

Motor

DM556 Driver

24VDC

B+

B

Figure 10 Wiring diagrams

to help new students get familiar with the controls of various motors Base on this papers, you can learn more about the control mechanism of DC servo motor, and stepper motor, since then there can be the foundation to develop the system on your own later In addition, the design of the stepper motor for provides a constant holding torque without the need for the motor to be powered and provided that the motor is used within its limits, positioning errors don't occur, since stepper motors have physically pre-defined stations

5.2 Motion controller board

To carry out combinational operations of the robot, an Arduino Mega 2560 board is used to synchronize 4 motors The connection between the drivers and the controller is demonstrated in general schematic as show in Fig.11

MCU

DC POWER 24V

DM556

DCS810

DCS810

DM556

DC DC CONVERTER

DC SERVO

DC SERVO

STEPPER MOTOR

STEPPER MOTOR

LED INDICATION

CONTROL BUTTONS

24V

24V

24V

24V

24V

Figure 11 General schematic

By using the DC DC converter to convert 24V to a lower voltage that allow MCU (here

is the Arduino Mega2560) able work well without heat! Command is given from Control buttons to MCU to issue required PFM to control these drivers and move the motors to a specific position that programed before Led indications are used to display the power status and errors during operation

5.3 Pulse Width Speed and Direction Control

The rotational speed of a DC motor is directly proportional to the mean (average) voltage value on its terminals and the higher this value, up to maximum allowed motor volts, the faster the motor will rotate In other words more voltage more speeds By varying the ratio between the “ON” (tON) time and the “OFF” (tOFF) time durations, called the “Duty Ratio”,

“Mark/Space Ratio” or “Duty Cycle”, the average value of the motor voltage and hence its rotational speed can be varied For simple unipolar drives the duty ratio β is given as:

Figure 12 DC motor duty cycle

and the mean DC output voltage fed to the motor is given as: Vmean = β x Vsupply Then by varying the width of pulse a, the motor voltage and hence the power applied to the motor can be controlled and this type of control is called Pulse Width Modulation or PWM

Another way of controlling the rotational speed of the motor is to vary the frequency (and hence the time period of the controlling voltage) while the “ON” and “OFF” duty ratio times are kept constant This type of control is called Pulse Frequency Modulation or PFM and this is also the method that we used to control the 2 driver DCS810 and DM556 [4] With pulse frequency modulation, the motor voltage is controlled by applying pulses of variable frequency for example, at a low frequency or with very few pulses the average voltage applied to the motor is low, and therefore the motor speed is slow At a higher frequency or with many pulses, the average motor terminal voltage is increased and the motor speed will also increase

The direction of our motors is determined by the value of DIR input port of drivers Changing the value of DIR port will change the rotate direction of motors

5.4 Orbital motion of Robot Palletizer

Based on the requirements of the actual loading and unloading, the authors will set the algorithm flowchart for showing the working steps of the robot, then use that to program the robot to work automatically The sequence of the robot work is as follows:

Step 1: When button Start is pressed, all the actuators will move to the zero position by

hitting the relays (CT1 = CT2 = CT3 = CT4 = on)

Step 2: Check for existed pallet and products at in the awaiting & loading position

If:

There is no signal from product (CB1 = off) or no signal from pallet (CB2 = off) or the pallet was full (CB3 = on) the robot will stop and wait for next command

Signal from product is received (CB1 = on), signal from pallet is also available (CB2 = on) and pallet is not full (CB3 = off) then robot move to step 3

Step 3: Sort 6 layers (0 <k ≤6) of products onto pallets at the position P (xi, yj, zk)

If:

- k is an odd number (k = 1, 3, 5) then sort the products into 3 columns and 2 rows in order row first then column next until completion (i = 3, j = 2)

- k is even number (k = 2, 4, 6), then sort the products into 2 columns and 3 rows in order row first column next until completion (i = 2, j = 3)

Step 4: After done with 6 layers the robot will come back to step 2 if there’s no stopped

signal

Step 5: Ending the cycle of loading and unloading

In the process robot will stop when received the control signal from button pause Loading and unloading process is illustrated in Figure 13 and flowchart algorithm is illustrated in Fig 14

Về chuẩn

Vị trí chuẩn

Vị trí sản phẩm

Vị trí pallet

Vị trí sản phẩm được sắp lên pallet

Figure 13 Loading and unloading process a) Gripper head go to zero position then move to products position

b) Gripper head pick up and move product to arranged place on the pallet

Start

Start is pressed

Go to zero position

Initialize

parameters

ALL CT are on

Check for signals of product and pallet

Yes

Yes No

CB1&CB2 are On CB3 is Off

Pickup product at A(x A , y A , z A ) Put onto pallet at P(x P , y P , z P )

PAUSE

Yes

No

No

Stop all actions

Yes

B

k > 6

k = k+1; Reset I, j=0

STOP Yes

Yes END

C

B No

No

No

K is odd number Yes No Arrange products in

2 columns and 3 rows

I = 2, j = 3

Arrange products in

3 columns and 2 rows

I = 3, j = 2

C

A

A

Figure 14.Flowchart control algorithm

6 SIMULATION

Motion simulation of the robot is useful to verify the kinematic analysis A module Simmechanics link in Matlab is used to convert from CAD models in XML format to Simulink diagrams in SLX format as seen in Fig 15a

CS3 CS2

De-1

Khung-1

CS3 CS4 CS2 Thanh truot ngang-1

Thanh truot dung-2

CS2

CS3

CS4

Tay 1-Dung-1

TAY 2-Ngang-1

CS3 CS2 CS4 Tay 3-1

CS2 CS3 Noi R1-1

Noi R2-2 CS3 CS2

Noi ngang-dung-2

tay gap cuoi-1

Khau Cuoi old-4

CS3 CS2 Noi R3-3

CS2 CS3 RootPart

RootGround

Prismatic

Revolute

Revolute1

Revolute2

B F Revolute3

B F

Prismatic1

B F Revolute4

B F Weld

B F Revolute5

B

F

Revolute6

Revolute7 B

F Revolute8

B F Revolute9

B F Revolute10

B F

Revolute11

Revolute12

B F Revolute13

B F Weld1

Env Machine Environment

1

Constant0 0 Joint Actuator 1

Constant1

Joint Actuator 2

Joint Actuator 3

Joint Actuator 4

Body Sensor

pos

From Workspace

Conn1

Conn2

Conn3

Conn5 Conn4

Robot

1

Constant2 0

Constant3

1

Constant4 0

Constant5

1

Constant6 0

Constant7

X

Y

Z

Figure 15 Robot model in Matlab and Joint actuators and body sensors attached

Motion at the joints are generated by blocks of joint actuator They are also monitored

by blocks of body sensor as illustrated in Fig 15b With this block diagram, as the robot is programmed to move from point to point at specific times and signals from body sensors can

be collected and seen in Fig 16

t2

t 3

t 1

t 3

t 4

Figure 16 Simulation process and results

7 EXPERIMENTAL RESULTS

Figure 17 Experimental procedure on the horizontal axis

This section will empirically evaluate the issues of decoupling between two actuators in x direction and z direction Figure 18 shows an experimental process to validate vertical errors while the end-effector moves a distance of 450 mm along x direction at three lifting levels 256

mm, 380 mm, and 500 mm Experimental results in Table 2 show that vertical errors are from 2,2 mm to 2,26 mm In addition, error patterns at three altitudes are almost the same

Do similarly, data in Table 3 show experimental results while the end-effector moves a distance of 500 mm along z direction at three reaching levels 400 mm, 600 mm, and 850 mm The results show that horizontal errors are from 3.24 mm to 3.28mm In addition, error patterns at three reaching levels are almost the same

Table 2: Experimental results on the horizontal axis Position

(mm)

Error, ∆Z

0 1 2 3

0 1 2 3

0 1 2 3

Table 3: Experimental results on the vertical axis Position

Error, ∆X

9 8 7 6 5 4 3 2 1 0

0

9 8 7 6 5 4 3 2

1

0

0

9 8 7 6 5 4 3 2

1

0

CONCLUSIONS

The paper proposed a type 4-DOF robots based on parallelogram structures A prototype has been developed to verify its decoupled motions and accuracy The experimental results show that the vertical error is 2.26 mm and horizontal error is 3.28 mm within the

investigated area of 450 mm × 500 mm These values are quite large but acceptable for loading and unloading applications

REFERENCES

[1] Patrik Gustafsson-Skoglund,Karl Södereng Container Unloading using Robotized

Palletizing, M A thesis, Chalmers University Of Technology, Sweden, 2012

[2] Michael G Kay, Material Handling Equipment, North Carolina State University

[3] Ph D Phạm Công Bằng, Bài giảng Robot công nghiệp, University of Technology

[4]

http://www.leadshine.com/productdetail.aspx?type=products&category=servo-products&producttype=brushed-servo-drives&series=DCS&model=DCS810

AUTHOR’S INFORMATION

center, Viet Nam - {vanlinhkh, buiquangvinh1712, babentanh}@gmail.com

2 Xuan Hao Nguyen, Cong Bang Pham - Faculty of ME, HCMC, Viet Nam - {21000883,

cbpham}@hcmut.edu.vn

3 Viet Anh Dung Cai - Faculty of ME, HCMUTE, Viet Nam - dungcva@ hcmut.edu.vn