Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV STUDY, DESIGN AND CONTROL ROBOT PALLETIZER NGHIÊN CỨU, THIẾT KẾ VÀ ĐIỀU KHIỂN ROBOT GẮP HÀNG Van Linh Tran 1a, Quang Vinh Bui 1a, Tuan Anh Nguyen 1a, Xuan Hao Nguyen 2b, Cong Bang Pham 2b, Viet Anh Dung Cai 3c Saigon Hi-Tech Park, R&D center, Viet Nam Faculty of Mechanical Engineering, HCMC University of Technology, Viet Nam Faculty of Mechanical Engineering, HCMC University of Technology and Education, Viet Nam 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 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 ứng dụng nhiều lĩnh vực khác nhờ vào tính ổn định, khả thích ứng linh hoạt tính xác vận hành Bài báo giới thiệu loại robot sử dụng phổ biến ứng dụng xếp dỡ Robot có bậc tự do, có cấu trúc dẫn động tách riêng theo phương chuyển động ngang chuyển động thẳng đứng Trong báo này, nhóm tác giả xin giới thiệu quy trình hoàn chỉnh để thiết kế robot gắp hàng, bao gồm thiết kế ý tưởng, phần điện tử, chế tạo nguyên mẫu đánh giá xác Từ khóa: robot công nghiệp, robot gắp hàng, hệ thống điện tử 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 degrees of freedom (DOF), including revolute joints and 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 This is followed by kinematic analysis in section Mechanical design and electrical design are addressed in section and section 5, respectively Simulation results to verify the kinematic analysis are validated in section Experimental results to evaluate accuracy are discussed in section Finally, section concludes the paper 130 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV a) b) Figure Loading, unloading crafts and by robot [1] CONCEPTUAL DESIGN To perform loading and unloading tasks, the robot structure must have abilities to:  Raise and move objects in 3-dimensional space X, Y, Z (from production lines), and then arrange them onto pallets as illustrated in Fig  Redirect objects and sort them in a neat order of each column, in multiple interwoven layers or in a pillow under the circle, as illustrated in Fig end-effector products Pallets conveyors Figure Picking up product from conveyors onto pallets Figure Typical arrangement of products on pallet [2] With the given requirements, the robot mechanism must have at least 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 In this mechanism, parallelograms can be observed such as AKLB, AHGB, and BFEC L G F B dc lx E D C φ2 lz P K H A M dz N dx I o φ1 Figure 4-DOF mechanism for robot palletizers 131 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV To simplify the kinematic analysis, link lengths are designed under the constraint in Eqn (1) 𝐼𝐾 = 𝐼𝐿 𝐿𝐵 𝐿𝐶 = 𝐾𝐴 𝐿𝐶 =𝑎 (1) 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 𝐴𝑀 = 𝐴𝐶 𝐴𝑁 𝐼𝑀 = 𝐶𝑁 = 𝑎−1 (2) KINEMATIC ANALYSIS Kinematic analysis of robots is to establish the relation between the joint angles / offsets (φ1, φ2, dx, dz) and the posture of the end-effector (x, y, z, β) 3.1 Forward kinematic {Q} YQ XQ ZQ Z0 {0} Y0 X0 dx dz l1 φ1 Figure Assigned frames to locate point P As discussed in section 2, the position of the end-effector (x, y, z) is only affected by joint parameters φ1, dx, and dz [3] Based on the relation of coordinate frames {0} and {Q} in Fig 5, together with Eqn (2), the position of the end-effector P can be derived: 𝑥𝑃 = (𝑎𝑑𝑥 + 𝑙𝑥 − 𝑙1 ) cos 𝜑1 { 𝑦𝑃 = (𝑎𝑑𝑥 + 𝑙𝑥 − 𝑙1 ) sin 𝜑1 𝑧𝑃 = −(𝑎 − 1)𝑑𝑧 − 𝑙𝑧 (3) The results in Eqn (3) show that the position of the end-effector only depends on dx when it moves horizontally and only depends on dz when it moves vertically For the orientation of the end-effector (β), it is only affected by joint angles φ1 and φ2 Fig 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: 𝛽 = 𝜑1 + 𝜑2 Z0 {0} (4) Z1 Y0 {1} Y1 X1 D X0 φ2 Z2 {2} φ1 Y2 X2 P O Figure Assigned frames to orientate the end-effector 132 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV 3.2 Inverse kinematic By combining Eqns (3) and (4), the solution of the inverse kinematic is determined as follows: 𝑑𝑥 = + 0𝑦 −𝑙 +𝑙 √ 𝑥𝑃 𝑃 𝑥 𝑑𝑧 = − 𝑎 ( 0𝑧𝑃 +𝑙𝑧 ) (5) (𝑎−1) tan 𝜑1 = 𝑦𝑃 𝑥𝑃 { 𝜑2 = 𝛽 − 𝜑1 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 √𝑑𝑥2 + 𝑑𝑧2 < 𝐼𝐾 + 𝐾𝐴 (6) MECHANICAL DESIGN This section employs the theoretical basis in section and the results of kinematic analysis in section to design link lengths of the robot palletizer that encloses a given workspace as illustrated in Fig With this desired workspace, link lengths are calculated and shown in Table Table 1: Link lengths of the robot palletizer F E G C B K H lx Dimensions D lz A I Unit (mm) P AB 400 500 L AH 80 LB 110 BF = BG 80 LC 550 CE 80 EF 440 LI 500 l1 103 lx 85 lz 135 l1 o 400 850 Figure Illustration of robot workspace Figure 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 Then, a prototype of the robot palletizer is fabricated as demonstrated in Fig 133 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV Figure Prototype of the robot palletizer ELECTRICAL DESIGN 5.1 Actuators In order to drive the robot, DC servo motors, with DCS810 drivers, are employed to control linear motions (dx, dz) and stepper motors driven by DM556 drivers are employed to create rotary motions (φ1, φ2) Their wiring diagrams are highlighted in Fig 10 VCC 24VDC GND VCC EA+ EA- DCS810 Driver 24VDC GND NC EB+ EB- DM556 Driver NC E+5V Gnd VCC Ch-B Motor - DC Servo Motor Stepping Motor B+ B- EGND Motor + A+ A- Ch-A Encoder a) Servo motor and DCS810 driver b) Stepping motor and DM556 driver Figure 10 Wiring diagrams The purpose of using use of two DC motors combined with two stepping motors here is 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 motors The connection between the drivers and the controller is demonstrated in general schematic as show in Fig.11 LED INDICATION DC POWER 24V 24V DCS810 DC SERVO DCS810 DC SERVO DM556 STEPPER MOTOR DM556 STEPPER MOTOR 24V DC DC CONVERTER MCU 24V 24V 24V CONTROL BUTTONS Figure 11 General schematic 134 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV 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 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 135 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV Step 3: Sort layers (0 6 Yes ALL CT are on Yes A C B No STOP Yes END Figure 14.Flowchart control algorithm 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 136 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV CS3 B F CS3 CS2 CS4 CS4 B F CS2 Revolute10 Tay 1-Dung-1 Revolute13 Tay 3-1 CS2 F F F CS3 B F CS3 CS2 F B B B B Revolute Noi R3-3 Revolute2 Revolute7 Revolute8 B F CS2 B CS4 CS2 F pos From Workspace B F Revolute4 CS3 Revolute9 CS2 X Conn2 Joint Actuator Constant3 Conn3 Revolute12 Thanh truot ngang-1 B F CS2 CS3 B Noi R1-1 Revolute3 Revolute6 Weld1 Conn5 F Constant4 Revolute5 RootGround Y Body Sensor F Prismatic1 Khung-1 CS2 CS3 CS2 Constant2 Conn4 CS4 B CS4 Conn1 CS3 F Joint Actuator 1 B F B Constant1 Khau Cuoi old-4 Prismatic Constant0 Noi R2-2 CS3 CS4 CS3 CS2 TAY 2-Ngang-1 CS4 Noi ngang-dung-2 CS5 Revolute11 Thanh truot dung-2 CS2 CS3 Revolute1 Joint Actuator Z Robot Constant5 tay gap cuoi-1 F B CS3 CS2 B F CS2 CS3 F B Env Constant6 De-1 Weld Machine Environment RootPart Joint Actuator Constant7 a) b) Figure 15 Robot model in Matlab and Joint actuators and body sensors attached t2 t4 = 97,6s t3 t3 = 72,6s t1 t1 = 23.8s t0, t4 t2 = 48.8s 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 Figure 16 Simulation process and results EXPERIMENTAL RESULTS Z3 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 ∆Z Z2 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 Z1 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 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 show that vertical errors are from 2,2 mm to 2,26 mm In addition, error patterns at three altitudes are almost the same 137 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV Do similarly, data in Table 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 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 0,22 0,48 0,72 0,98 1,22 1,5 1,74 1,98 2,26 1,78 2,24 1,72 1,96 2,2 Z3 (500) 0 0,26 0,52 0,76 1,02 1,26 1,52 Z2 (380) 0 0,24 0 0,74 1,24 1,46 Z1 (256) 0 Table 3: Experimental results on the vertical axis Error, ∆X Position X1 (400mm) X2 (600mm) X3 (850mm) Z0 0 Z1 0,36 0,34 0,38 Z2 0,74 Z3 1,06 0,72 1,08 1,42 1,82 2,16 Z4 1,44 Z5 1,78 Z6 2,18 Z7 2,52 Z8 Z9 0,76 1,1 1,46 5 1,8 2,18 2,5 2,54 2,88 2,9 2,88 3,24 3,26 3,28 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 138 Kỷ yếu hội nghị khoa học công nghệ toàn quốc khí - Lần thứ IV 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=servoproducts&producttype=brushed-servo-drives&series=DCS&model=DCS810 AUTHOR’S INFORMATION Van Linh Tran, Quang Vinh Bui, Tuan Anh Nguyen - Saigon Hi-Tech Park, R&D center, Viet Nam - {vanlinhkh, buiquangvinh1712, babentanh}@gmail.com Xuan Hao Nguyen, Cong Bang Pham - Faculty of ME, HCMC, Viet Nam - {21000883, cbpham}@hcmut.edu.vn Viet Anh Dung Cai - Faculty of ME, HCMUTE, Viet Nam - dungcva@ hcmut.edu.vn 139 ... Cuoi old-4 Prismatic Constant0 Noi R 2-2 CS3 CS4 CS3 CS2 TAY 2-Ngang-1 CS4 Noi ngang-dung-2 CS5 Revolute11 Thanh truot dung-2 CS2 CS3 Revolute1 Joint Actuator Z Robot Constant5 tay gap cuoi-1 F B... GND VCC EA+ EA- DCS810 Driver 24VDC GND NC EB+ EB- DM556 Driver NC E+5V Gnd VCC Ch-B Motor - DC Servo Motor Stepping Motor B+ B- EGND Motor + A+ A- Ch-A Encoder a) Servo motor and DCS810 driver... quốc khí - Lần thứ IV a) b) Figure Loading, unloading crafts and by robot [1] CONCEPTUAL DESIGN To perform loading and unloading tasks, the robot structure must have abilities to:  Raise and move