FPGA Implementation of Closed Loop Control of Pan Tilt Mechanism

Transcription

1 IJCTA, 9(39), 206, pp International Science Pre Cloed Loop Control of Soft Switched Forward Converter Uing Intelligent Controller 295 FPGA Implementation of Cloed Loop Control of Pan Tilt Mechanim N.R. Senthilnathan* Siddharth V., A. Shahul Hameed* S. Mohammed Mutafa* S.Pon Karthikeyan* Padmanabhan A.* and A. Britto Shibi* Abtract : In automated urveillance ytem with camera, the ytem mut be able to poition the camera accurately. The camera mut be able to pan and tilt uch that an object detected in the cene i in a vantage poition in the camera image plane and ubequently capture image of that object for further analytic kind of information. Thi paper preent the detail of a Field Programmable Gate Array (FPGA) implementation of cloed loop control of pan and tilt angle of the camera mount uing ervo motor a actuator and compact RIO from National Intrument a the controller. The controller i programmed uing the LabVIEW FPGA oftware. The paper preent the detail of the mechanical deign, hardware pecification, modelling information and control information detail. The main objective i to perform poition and velocity control of pan and tilt axi motion i to get accurate poition and velocity. Keyword : FPGA, Real Time Control, Pan-tilt, Servo motor control, Modelling, Simulation.. INTRODUCTION Pan-tilt head i a 2-axi mechanim which i often ued in imaging ytem to keep an object of interet in the field of view of the camera. The poition and velocity of the pan tilt head are very important parameter ince they determine the field of view in the cene and alo match the velocity of any moving object in the real world. The pan-tilt head find application in urveillance, automated video recording and video analytic in general. Video captured by manual adjutment of pan and tilt angle are often accompanied by frame drop. Motorizing the pan-tilt head reduce the rik of the camera operator introducing any jerkine or vibration to the hot during a pan or tilt. In automated cae motorizing the two axi i the norm. Numerou literature i available in the context of control of pan-tilt epecially related to viual tracking ytem, automated urveillance, olar tracking, video conferencing, live production, lecture capture and ditance learning and when attached with a enor it i ued to detect object and for meaurement of ditance at variou point by controlling the pan and tilt angle in robot among many other. Automatically controlling the pan and tilt angle remove the need for a camera operator a it pan and tilt a the ubject move. Camera with motorized pan tilt head over tationary camera ha it advantage in that the field of view can be changed whenever neceary intead of the need for manual adjutment of the mounting angle. Camera attached to motorized pan tilt head offer the ability to capture footage at multiple angle and perpective while urveying a wide range of territory. Thi paper preent the detail of implementation of cloed loop poition and velocity control of two degree of freedom pan-tilt mechanim in Field Programmable Gate Array uing LabVIEW a a development platform. The motorized pan-tilt head generally conit of two ervo motor for pan and tilt motion. They are controlled uing compact RIO 9074 controller with two 9505 ervo motor drive module from National Intrument. Thee module give full H-bridge control of the DC ervo motor. The crio controller i programmed uing LabVIEW uing LabVIEW FPGA package which help create the hardware definition language code for * Department of Mechatronic Engineering, SRM Univerity, Kattankulathur , Tamil Nadu, India enthilnathan.r@ktr rmuniv.ac.in

2 296 N.R. Senthilnathan, Siddharth V., A. Shahul Hameed, S. Mohammed Mutafa, S. Pon Karthikeyan... the Xilinx FPGA on board the crio controller. The motor are controlled by generating a PWM ignal to the motion control module and it i then tranlated to an analog voltage to command the motor. High accuracy and precie peed control can be achieved when the pan and tilt operation are controlled through the ervo motor. The paper i arranged in the following order which tart from mechanical deign detail of the pan-tilt mechanim, followed by the modelling and imulation of the DC motor ued in the pan and tilt axi, hardware pecification of the variou element ued and finally the FPGA implementation. 2. MECHANISM DESIGN The pan and tilt mechanim require a rigid bae and a mount for pan motor. A C-clamp i ued to mount the pan motor and provide a upport for the rigid bae. Along with the pan motor, the limit witche are placed on the top urface of the clamp. A flange i ued to link the tilt mechanim to the pan motor haft. The tilt motor i mounted on the flange uing L-clamp. The camera mount i fixed to the tilt motor haft through a flange. The initial model wa deigned uing flat plate but actual implementation i done uing channel. The pan axi motor mount i hown in Figure. Figure : Pan Axi Motor Mount and Flange The figure how the upport of the pan motor with the mechanical toppage and extreme poition marked on it. It i attached to the tructure bae. The figure alo how the pan flange which i connected to the haft of the pan motor. It how the home poition a well a the extreme poition extruded from it. 3. HARDWARE SPECIFICATIONS Figure 2: Complete Pan-tilt Mechanim The following ection of the paper decribe the variou pecification of the pan-tilt etup developed.

3 3.. DC Servo Motor FPGA Implementation of Cloed Loop Control of Pan Tilt Mechanim The pan and tilt axi are actuated by DC ervo motor with quadrature encoder whoe pecification are lited in Table. Thee motor feature extremely low inertia and zero cogging or preferred rotor poition, a well a a uniquely high, power to volume ratio. Table Specification of DC Servo Motor for Pan and Tilt Axi crio 9074 Controller Parameter Type Gearbox Ratio Load Current Power Speed No Load Current Encoder Type Encoder Phae Encoder Reolution Diameter Length Total Length Diameter of the Shaft Length of Shaft Stall Torque Specifi cation Faulhaber 2V DC Corele Motor 64: l Planetary 3 Stage Gear Box 400 ma 7W 20Rpm 75mA Optical AB 768CPR of Output Shaft 30mm 42mm 85mm 6mm 35mm 52 kg The CompactRIO 9074 real-time controller conit eight-lot reconfigurable chai into an integrated ytem. It ha the ability to be ynchronized on a network and alo feature a built-in backup battery to maintain operation for the Real-Time Clock when external power i removed. The chai can accept up to eight NI C Serie I/O module. A variety of I/O module are available including voltage, current, thermocouple, RTD, accelerometer, and train gauge input; up to 60 V imultaneou ampling analog I/O; 2, 24, and 48 V indutrial digital I/O; 5 V/TTL digital I/O; counter/timer; pule generation; and high voltage/current relay. In the propoed ytem, a ervo drive module and birectional digital module are ued in the chai. The crio controller alo have an Ethernet port that allow for programmatic communication over the network to a hot PC or enterprie ytem and the other port for expanion I/O DC Bruhed Servo Drive NI-9505 The NI 9505 C Serie module for NI Compact RIO i a full H-bridge ervo motor drive for direct connectivity to actuator uch a bruhed DC ervo motor. Thi module include a built-in encoder interface for ingleended or differential input for poition feedback from a quadrature encoder. It alo include a current enor you can ue to ample the current through the motor, or actuator, and read it through the FPGA in the CompactRIO chai. With function uch a trajectory generation and proportional integral derivative (PID) control featured in the NI SoftMotion Development Module for LabVIEW, it i poible to develop a complete reconfigurable motion control and drive ytem in a compact form factor with CompactRIO and LabVIEW and accurately control velocity and poition of DC Servo Motor. The module upport real-time data acquiition from the current enor for flexible ampling time and motor current filtering to 297

4 298 N.R. Senthilnathan, Siddharth V., A. Shahul Hameed, S. Mohammed Mutafa, S. Pon Karthikeyan... optimize the control loop. The nine-pin D-Sub connector on the NI 9505 offer encoder input for poition and velocity feedback in addition to a +5 V connection for encoder power and an emergency top input B-directional Digital I/O NI-9403 The NI 9403 i a 32-channel, 7 bidirectional digital I/O module for NI Compact DAQ or CompactRIO chai. The direction of each digital line on the NI 9403 can be configured to be an input or an output. Each channel i compatible with 5 V/TTL ignal and feature,000 Vrm tranient iolation between the I/O channel and the backplane. In thi work the NI 9403 i programmed uing LabVIEW FPGA for interfacing CompactRIO with enor. Figure 3 how the illutrative photograph of the crio chai and the C-erie module ued in the developed ytem Optical Limit Switche Figure 3: Illutrative Photograph of crio Controller and C-erie Module A lotted opto-coupler i ued a a limit enor for homing and over-travel control. Since the ervo motor ued are incremental encoder type, mechanical homing become the norm. It meaure the phyical quantity of light and then convert it into a form that i readable by 9403 module. When the ignal i interrupted, the light enor operate a a photoelectric trigger and therefore give the electrical output. The pan motor and the tilt motor i rotated to home poition by reading the optical witche. The Figure 4 how the photograph of the complete ytem indicated with the variou ub-ytem element. Tilt Axi Limit Senor C-erie Module crio Chai Pan Axi Figure 4: Photograph of the Complete Sytem The hardware connection diagram indicating the connection of the variou enor and actuator to the controller and module are hown in Figure MODELLING AND SIMULATION OF MOTOR The pan-tilt mechanim i actuated by two identical DC motor. In order to perform a flawle control of poition and velocity, thorough undertanding of the ytem i required. A complete model baed undertanding of the motor i performed in the Simulink platform. The detail of the mathematical model development and imulation reult are preented in the following ection of the paper. The torque equation of the DC motor i given by []

5 FPGA Implementation of Cloed Loop Control of Pan Tilt Mechanim d K T I = J Bd () dt Thi equation can be written a 2 d k 2 = T Bd (2) dt J The current equation of the DC motor i given a v = I IR L d kb (3) dt di d Thi equation can be written a = vkb IR (4) dt L dt The differential equation can be imulated with armature voltage a input and poition and velocity a output. Figure 5: Hardware Connection Diagram of the Propoed Sytem The parameter of the Faulhaber DC motor acquired from the dataheet are a follow: Table Specification of DC Servo Motor for Pan and Tilt Axi Parameter Reitance Inductance Back-emf Contant Torque Contant Specifi cation.9 65 H.4 mv/rpm 3.4 mnm/a Rotor Inertia 5.7 gcm 2

6 300 N.R. Senthilnathan, Siddharth V., A. Shahul Hameed, S. Mohammed Mutafa, S. Pon Karthikeyan... Now, the tate variable are x = ; x2 ; x3 I (5) The tate equation i given by [2] x = Ax + Bu(t) (6) 0 0 x B 0 when ubtituted with value x J V x 3 kb R I 0 L L L The Simulink model of the differential equation i hown in Figure 6: = u t (7) -K- Kt + Add Divide Integrator Integrator2 Out In -K- Kb 0.00 Mr.9 5.7e-7 J + Add 65e-6 L Divide Integrator w L 2 Out2 R i i Figure 6: Simulink Model of the DC Motor Theimulation reult how the time plot of the haft poition and peed of the DC motor for a applied voltage i hown in Figure 7. The plot i baically a tep repone graph for the poition and velocity. 200 Step Repone From: V liny To: Subytem/ Amplitude To: Subytem/ Time(econd) Figure 7: Time Plot of Poition and Velocity

7 FPGA Implementation of Cloed Loop Control of Pan Tilt Mechanim The output equation i given by y = Cx + D (8) The tranfer function can be obtained by uing y = (9) I The obtained tranfer function for velocity control i [3] C [I A]. B (0) 0 0 O B J V kb R 0 L L L 0 0 B O C 0 0 where A = The obtained tranfer function for the poition control i given by TF = 38* *0 480 The tranfer function for the velocity control obtained from the model i given by TF = 8 367*0 2293*0 4837* The tranfer function for the poition control obtained from the model i given by TF = *0 4837* *0 8 () (2) (3) (4) 5. FPGA IMPLEMENTATION Many PC baed control of DC ervo motor have been reported in the literature [4, 5]. In the current work, deired pan and tilt angle are kept a et point in the LabVIEW front panel. A proportional control i developed which ue the preent error between the actual pan- tilt angle with the deired angle. Then the motor are rotated accordingly in order to obtain the deired pan and tilt angle. LabVIEW FPGA oftware module i ued to read the quadrature ignal and write drive ignal to the 9505 C-erie module for motor drive. Direct FPGA I/O read method i adopted ince the algorithm i meant to run in the FPGA of the crio and not in the real time controller. The LabVIEW code i a graphical implementation of the control algorithm to control the input given to the pan and tilt motor. The encoder ignal are received and converted into incremental value. Since a 2 CPR encoder i ued and the peed reduction i ratio 64: there are 3072 pule for each rotation of the output haft. The deired angle i alo converted to equivalent count value auming a 2CPR encoder. Thi value will be compared with the encoder value obtained from the encoder feedback. And the poition control i achieved. The direction of rotation i given by the ign of the input angle. For velocity control the power input given to the motor i given in the form of Pule-Width Modulated (PWM) ignal. The LabVIEW graphical code i developed for the poition and velocity control are hown in Figure 8.

8 302 N.R. Senthilnathan, Siddharth V., A. Shahul Hameed, S. Mohammed Mutafa, S. Pon Karthikeyan CONCLUSION Figure 8: LabVIEW code for poition and velocity control The developed etup can be further ued in the field of viual tracking, which i the original intent for the development of the propoed work. It i the field which combine reult from many field like imaging, high peed image proceing, real time computing. The performance of the viual tracking ytem relie the effectivene of he motion control ytem. The FPGA implementation exhibited highly conitent reult in term of the time performance, though from accuracy tandpoint lape were noticed due to the aymmetry in the encoder wheel ued in the motor. The FPGA implementation ha one of the ignificant advantage of zero computational overhead enuring a true real time performance. Thi i mainly attributed to the no oftware ued in the control uch a operating ytem or aembly code. The future work in the project i to integrate a viion ytem with motion control for performing a viual tracking of moving object in the field of the camera attached to the pan-tilt ytem developed. 7. REFERENCES. B.C. Kuo, Automatic Control Sytem, John Wiley & Son, W.P. Aung, Analyi on modeling and imulink of DC motor and it driving ytem ued for wheeled mobile robot, World Academy of Science Engineering and Technology, Vol. 32, pp , D. Xue, Y. Chen and D.P. Atherton, Linear Feedback Control Society of Indutrial and Applied Mathematic, K.A. Naik and P. Shrikant, Stability enhancement of DC motor uing IMC tuned PID controller, (IJAEST) International Journal of Advanced Engg. Science and Technologie, vol. 4, no., pp , G. Haung and S. Lee, PC baed PID peed control of DC motor, Proc. of International Conference on Audio Language and Image Proceing (ICALIP-2008), pp , 2008.