Scanning Manipulator: Version 1

Figure 1. Drawing of the prototype

The DYLEMA project uses a sensor head based on a metal detector, which is a device that senses a single point or very small areas.  A scanning device is therefore needed that can sweep the sensor across large areas.  The easiest system would be a manipulator tailor-made for this task.  Such a manipulator would require three DOFs for positioning the sensor in a 3D area; assuming that the system is scanning a non-flat area, motions in the x, y and z components would be required.  Also, the detector would have to be adapted to small terrain inclinations; hence, two additional DOFs would be needed at the wrist to control detector attitude.  The detector has radial symmetry, so no additional DOFs would be needed for orientation control.  To sum up, a manipulator with at least five DOFs is needed to accomplish the task.

The manipulator is designed to carry the sensor head, so the design is optimised to carry just this load.  First, the load is balanced to move the detector ±45º in its pitch and roll wrist axes with the lower torque.  This is accomplished by placing the detector in a configuration in which no torque is required in the normal position (detector levelled at rest).  In the manipulator, a RRR arm configuration is good enough for this application.  Mobility is adequate and, because the links lie along a single vertical plane, there will be less collisions with the environment (assuming the robot’s body is levelled).  Another key design point is to mount the joint motors at the required position to balance the loads and decrease required torques.  Figure 1 shows a detailed design of the scanning manipulator taking into account the aforementioned design requirements.  Figure 2 shows a picture of the manipulator prototype. Video 1 shows the preliminary experiments with the scanning manipulator. Table 1 lists the manipulator’s features.  Some of these features, such as manipulator-link lengths, depend on the robot’s dimensions (body height and leg span).

Figure 2. Scanning manipulator

Video 1. Testing the manipulator

Table 1. Main scanning manipulator features (Version 1)

The first version of the scanning manipulator was developed in the first phase of the DYLEMA project and designed to carry only the sensor head. The second phase of the DYLEMA project is devoted to applying the system to irregular terrain containing weeds and small bushes, so a small grass cutter is required. The first version cannot carry the extra load of the grass cutter; therefore a new scanning manipulator has been designed.

The new manipulator estructure is quite similar to the former one. It consists of 5 rotary joints; however, joints 2 and 3 are coupled through a differential system that let two motors to contribute to the torque of one independen joint. This is a kind of parallel system that reduce the maximum torque supplied by the motors.

The grass cutter is placed as indicated in Figure 3. Thus, joint 4 must rotate more than 180 degrees to put both sensor head and grass cutter in the operation position. Joint 5 relies on a spirsin reducer to decrease the backlash. Figure 3 shows a drawing of the manipulator indicating the joints and links. Figure 4 depicts the manipulator and Table 2 presents the features of the new manipulator. Video 2 shows the first experiments with this new prototype.

Figure 4. Scanning manipulator prototype

Video 1. Manipulator: tests on laboratory (SpeedX10)

Video 2. Manipulator: tests on natural terrain (SpeedX10)

Video 3. Manipulator and Sensor Head scanning an irregular terrain with different textures (SpeedX10)

Table 2. Main scanning manipulator features (Version 2)