Experimental Setup and Results

Experimental Setup and Physical Constraints

The 3D CAD design of the Capsubot (without Capsubot-shell) is shown in Fig. 3.10(a). A prototype shown in Figs. 3.10(b) and 3.10(c) is developed based on the design and the proposed trajectory tracking control is implemented in the developed prototype. In the ex- perimentation, segment time T=1s is used. The main components of the developed capsubot system are a linear DC motor (QUICKSHAFT LM1247-020-01), a motion controller [181], two batteries and a capsubot-shell to hold all the components. The linear motor is com- prised of a motor-housing which houses the coil, three hall sensors and a cylindrical rod which is capable of moving back and forth within the capsubot. The motion controller provides power to the linear motor and controls the movement of the cylindrical rod by controlling the current flow to the motor coil. The coil is placed inside the motor housing and peripheral to the cylindrical rod. Two batteries provide power to the motion controller. The motion controller is programmed using the Motion Manager Software [181] and then can be disconnected from the PC. The capsubot is 20cm in length and 8cm in diameter. The cylindrical rod works as the Inner Mass (IM) of the capsubot.

It is noted that the IM includes the cylindrical rod and two extra masses (adhesive tack) at both ends of the cylindrical rod. The extra masses are added to increase IM to capsubot mass ratio. The parameters of the capsubot are listed in Table 3.1. The Hall sensors are used to determine the position of the cylindrical rod (IM). The linear motor data (i.e. IM position and velocity, and current through the coil) can be logged using the Motion Man-

3.5 Simulation, Experiments and Analysis 69

ager software. To obtain the data for capsubot movements the motion of the capsubot are recorded using a video camera and then a video analysis software Quintic Biomechanics [182] is used. It determines the position, velocity and acceleration of the capsubot.

The capsubot has the following physical constraints:

• The stroke length of the IM is 20mm [181] (Figs. 3.10(a)and3.10(c)). In the experi- mentation and simulation stroke length of 18 mm (_{−k ≤ x}m−xM≤ k where k = 9mm)

was used to avoid the collision. This constraint was considered while designing the profile parameters tc1, tc2, tu1, tu2, tu3 and tu4 of Fig.3.3.

• The maximum achievable continuous acceleration of the IM is_±30ms−2. This limit was considered while designing the profile parameters amu2, amu3 and amc1 of Fig.

3.3.

• The maximum static friction force of the capsubot is µMMg. This constraint was

considered while designing the profile parameters amu1, amu4 and amc2 of Fig. 3.3(a)

and3.3(c).

• Other constraints of the linear motor (LM 1247-0201-01) from the data sheet [181]: – Maximum continuous force on the IM : 3.09 N

– Peak force on the IM : 9.26 N

– Maximum continuous current through the motor coil: 0.48 A – Peak current through the motor coil : 1.44 A

The above mentioned constraints are met when acceleration is used within the limit

±30ms−2. System Calibration

The components of the capsubot that are involved in the calibration process are the mo- tion controller, the linear DC motor (QUICKSHAFT LM1247-020-01) [181] and the hall sensors. To calibrate the hall sensor signals the built-in capability of the motion manager software [181] is used. Calibration of the hall sensor signals is necessary to optimally adjust the motion controller to the connected linear motor. The linear DC motor is connected to a PC through the motion controller where the motion manager software is installed. Before starting the calibration, it is ensured that the rod is in the middle of its traversing path and can be freely moved over the whole traversing range. Then the motion manager software is

(a) 3D CAD design of the Capsubot (without Capsubot-shell)

(b) Implemented Capsubot: With capsubot-shell (Length: 20cm, Diameter: 8cm)

(c) Implemented Capsubot: Without capsubot-shell (Extra masses - blue tack - are added to the cylinder to increase IM to capsubot mass ratio)

3.5 Simulation, Experiments and Analysis 71

asked to calibrate the hall sensor signals. During the calibration process the cylindrical rod (IM) of the linear DC motor is positioned several times within its range limits. The software shows a message after successful completion of the calibration of the hall sensor signals. The optimized system parameters are saved in the motion controller memory by using the "EEPSAV" command in the motion manager software.

When the calibration is completed few test measurements are taken to verify the calibra- tion. The motion manager software is given the command "POS" which shows the current position of the cylindrical rod measured by the hall sensors. Then the cylindrical rod is asked to move to "+9mm" by using the command "LA". Then the command "POS" is used

to know the position of the cylindrical rod after the movement measured by the hall sensors. From the two measured positions the travelled distance by the cylindrical rod is calculated. The travelled distance is also measured by using a vernier caliper. The measured values are within "9_{± 0.02mm" for both the hall sensors and the vernier caliper measurements. The} complete process is repeated for five times and the measured values lie within "9_±0.02mm". The process is then repeated for a movement of "_{−9mm". The measured values lie within} "_{−9 ± 0.02mm". Thus the calibration of hall sensors along with the linear DC motor and} the motion controller are verified.

Creation and Use of the Database

The equations presented in section3.4.1are used to create the database for the implemen- tation. The parameters are used from Table3.1. The other parameters which are required for the creation of the database are presented in Table3.2. Using all the above information a database is created which have the format presented in Tables3.3and3.4for the utroque and contrarium profiles respectively. The selection algorithm is used for the selection of the acceleration parameter set from the database of Tables3.3and3.4to track the capsubot trajectory. This chapter proposes a segment-wise trajectory tracking and thus the complete trajectory is divided into many trajectory segments. The selection algorithm firstly cal- culates the required capsubot average velocity ( ¯˙x_Md(i)) for the current trajectory segment.

Then it selects the required profile (utroque or contrarium) to track the current trajectory segment. After that the selection algorithm compares ¯˙xMd(i) with all the ¯˙xMu (Table 3.3)

for the utroque profile and selects the parameter-set corresponding to that particular ¯˙xMu for

which ¯˙xMd(i) is the closest in magnitude. Same procedure is followed for the contrarium

profile. Then the inner mass uses the selected parameter set and thus capsubot tracks the current trajectory segment. For each trajectory segment the above procedures are repeated. When all the trajectory segments are tracked, the capsubot completes the trajectory tracking.

Table 3.2 Parameters of the developed capsubot to create the database

|amumax| |amumin| amudi f f |amu1| = |amu4| g

30ms−2 8ms−2 0.5ms−2 5ms−2 9.8ms−2 |amcmax| |amcmin| amcdi f f |amc2|

30ms−2 8ms−2 0.5ms−2 5ms−2

Table 3.3 Database for the utroque profile

Serial

number ¯˙xMu amu1 amu2 amu3 amu4 1

2 ..

nu

Experimental Results

The capsubot tracks a semi-circular position trajectory on a plywood table. Fig. 3.11(a) shows the experimental position of the IM for the capsubot trajectory tracking. From Fig. 3.11(a), it is observed that the IM moves within the limit i.e. [-k, k] where k is 9mm. Fig. 3.11(b)shows the experimental position trajectory of the capsubot. From Fig. 3.11(b), it is observed that the capsubot trajectory is not smooth rather it goes step by step. The reason behind this is the very nature of the capsubot movement principle where capsubot moves part of each cycle and remains stationary for the remaining time of the cycle. If a smaller segment time is used, the smoothness of the trajectory tracking will improve.