- Ceilbot - Trunk Manipulator. AS Automation- and systems technology project work Autumn Intermediate Report

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1 - Ceilbot - Trunk Manipulator AS Automation- and systems technology project work Autumn 2010 Intermediate Report Matthias Fueller October 31,

2 Introduction This intermediate report summarises the actual work which was done so far in this project and compares the initial project plan with the actual project workflow. Goal of the project This project is arranged under the umbrella of the ceilbot project [4] and focuses on the development of a first prototype of a continuum manipulator. It evaluates state of the art techniques in continuum manipulation and choose one approach as a basis for an own model. This prototype is then used to evaluate the application of such a trunk like manipulator for the ceilbot project. The prototype will not be controllable by actuators, instead it will be controllable by manual interaction like using a marionette. The focus lies onto the design of the manipulator prototype and the feasibility of the construction. Project Review The project review is based on the tasks which are defined in the project plan [5]. 1. State of the art analysis of continuum manipulators 2. Design choose of one practical construction approach 3. Detailed design of the manipulator prototype 4. Material purchasing / construction 5. Construction 6. Evaluation of manipulator 7. Documentation Up to know, only the first four point are worked out. The last three point follow after the material purchasing is completed. State of the art analyses of continuum robot manipulators The project started with an survey of existing trunk manipulator approaches. [11] divide existing manipulators into three different groups. Discrete, serpentine and continuum manipulators. Figure shows a sketch of these types. Discrete mechanisms (left) consists of some rigid links which are connected by joint. They provide a good motion speed and a high accuracy. Additionally they can be easily constructed for high payloads and the kinematics are quite simply. The 2

3 Figure 1: Different types of manipulators, based on [11] counterpart are the high weight due to the stiff link and the limited manoeuvrability due to the few joints. Serpentine manipulators (middle) use also utilise discrete joints but they use many short rigid links with a high density of joints. Due to the usage of more joints, these robots provide a better manoeuvrability and a better obstacle avoidance. The downside are the higher complexity due to the amount of joints. The third group are the continuum robots (right) which structure is able to bend continuously and produce motion through curving the manipulator. Continuum robots offer a good manoeuvrability and are able to reach difficult positions. Depending on their constructions, they can be lightweight. Unfortunately, the payload is not very high and the kinematics are quire difficult. Furthermore, the accuracy of the manipulators are not good ad the discrete and serpentine manipulators. Due to the light weight construction possibility and the ability to reach difficult positions, the continuum robot style manipulator can be a good design choice for household robots. To evaluate the application, this project develops a first prototype of such a manipulator. The mechanical implementation if continuum robots differs basically in two areas. The first area is the way of the mechanical actuation of the manipulator, the second one of the manipulator axis. Literature like [11] and [7] distinguish intrinsic, extrinsic and hybrid approaches. In the intrinsic approach, the actuators are located directly on or in the arm. These actuators can be servos, hydraulic ([2]) or pressured systems.([1] [8]). The actuators on arm lead to a heavier manipulator weight since you need many actuators for a continuum bending. The second approach is extrinsic actuation. There, the manipulator is remotely actuated via mechanical links like cable or tendons. Example are presented in [3] [6] [9] [10] [12]. Its advantages are the light manipulator design. Disadvantages are the problem of the force transportation and friction. Hybrid approaches uses both types of actuation. The second main area in the mechanical implementation in continuum robots are the design of the axis. Basically, there are two different approaches, flexible axis and multi-link axis. The first one is the usage of a flexible axis like a rubber tube [10], a wire [3] or a hose [6] [9] (see figure ). The actuators like tendons are attached on the outer surface. The advantage of this implementation is that the construction is quite simple and the material is cheap and lightweight. The downside of this approach can be the external cable guide (in extrinsic case) which can be hard to attach. Additionally, some hose type manipulators can 3

Figure 2: Flexible axis approaches. (left) Rubber tube (center) hose (right) tendons are attached at 120 o on the surface of the tube/hose.

(left) example axis (right) sketch of a tendon guide disc [12] control the length of the manipulator which enables them to have a better manoeuvrability.

Another design approach is the use of a multi-link axis like presented in [12] (figure ). There, the axis consists of many connected links.

4 Figure 2: Flexible axis approaches. (left) Rubber tube (center) hose (right) tendons are attached at 120 o on the surface of the tube/hose. [9] [11] Figure 3: Multi-axis approaches. (left) example axis (right) sketch of a tendon guide disc [12] control the length of the manipulator which enables them to have a better manoeuvrability. But this technique require a complex design and a compressor to create high pressure inside the hose which lead the an extension of the manipulator. Another design approach is the use of a multi-link axis like presented in [12] (figure ). There, the axis consists of many connected links. These axis is like serpentine manipulator and indeed the identification can be somehow fuzzy if the actuators are intrinsic. In the continuum case, the density of the links is much higher and most of the actuators are controlled extrinsic. The advantage of the multi-link approach are the simple construction and the internal cable guidance. Downside can be the heavy weight of the joints which lead to a higher overall weight. 4

Figure 4: Figure of the selected joint type (http://maedler.

aspx) Design choice After the survey of the existing manipulator types was completed, the design choice had to been made to start the actual implementation of the manipulator.

5 Figure 4: Figure of the selected joint type ( d1 d2 d3 I1 I2 I3 w weight (mm) (mm) (mm) (mm) (mm) (mm) (mm) (g) Table 1: Dimensions of the selected joint type ( Design choice After the survey of the existing manipulator types was completed, the design choice had to been made to start the actual implementation of the manipulator. After two meeting were we discussed the design, we decided to build the prototype using extrinsic based actuation based on cables and a multi link axis. The decision for the extrinsic method was based on the more simpler complexity of the trunk. Intrinsic methods require more complex design and, since this is a first prototype to get clues about the application of a continuum robot, the intrinsic approach lead to a faster development of the prototype. The decision for the multi link axis was based on the first decision. The fixation of the cable guide on the surface of a flexible axis was not fully clear for us. Using glue on the flexible surface may cause cracks in the glue which lead to a failure. The multi link approach seems much better since you can fix the guidance between the joints. As already defined in the project plan, the manipulator will consists of two sections, each in-dependable controllable. Detailed design of the manipulator prototype After the design choice was made the detailed design for the manipulator had to be defined. The disadvantage of the heavy weight of the multi-axis approach is reduced due to the usage of plastic joints which weight only a fifth of metal joints. Details about the joints are shown in figure and table 1. One section of the final manipulator consists of 6 joints, each witch a maximum operating angle of 35 o, which lead to a maximum bending of 210 o of each section. The cable guidance discs had to be made on our own. The layout of the disc 5

Figure 5: Details of the cable guidance disc Figure 6: Sketch of a section of the final manipulator is shown in figure. The discs were made out of a PVC board.

The material of the cable for the actuation will be decided after the axis and discs are assembled. Different types of cables will be tested and compared.

6 Figure 5: Details of the cable guidance disc Figure 6: Sketch of a section of the final manipulator is shown in figure. The discs were made out of a PVC board. In the current design with two sections, only 6 holes for the cable guidance would be necessary, the actual disc contain 12 holes for further extensions such as additional sections. The material of the cable for the actuation will be decided after the axis and discs are assembled. Different types of cables will be tested and compared. A sketch of one section of the final manipulator is shown in figure. A complete length of a section composed on the length of each joint (62mm) and the disc width (4mm). The length of one section is 6 62mm+6 4mm = 396mm and the overall length of the manipulator will be about 800mm. Material purchasing / construction As mentioned earlier, the joints are ordered and the tendon guidance discs are already made. After the order arrives, the construction of the manipulator will be continue. 6

7 Comparison of target and actual plan This section compares the initial plan which is described in [5] and the actual project workflow. The GANT chart is shown in figure 7. The state of the art analysis took one week more time than expected since the actual design choice could not be fixed on the first meeting. So the design choice was postponed to the next meeting. The detailed modelling of the trunk manipulator took two weeks as expected. Since the delay of the first task, the material could only ordered in CW 42 and is therefor not yet available. Luckily, the pre-construction of self-made parts took only one week and not three as planned. The main-construction part will start as soon as the joints arrive. The experience of the pre-construction task show that due to the good equipment available in the Design Factory of the Aalto University the construction tasks can be fulfilled faster than expected. That s why the authors see no problem in reaching the milestone of the first prototype in CW 46. Figure 7: GANT chart of project for target and actual planned activities Milestones Design choice (actual ) Intermediate Report ( ) First prototype Final presentation 7

8 Summary Due to the postponement of the design decision, the plan delays from the real workflow of about 1 week. The overall goal will not be influenced by this delay, since the construction of the should be doable within three weeks. References [1] T. Aoki, H. Ohno, and S. Hirose. Design of slim slime robot II (SSR-II) with bridle bellows. In Intelligent Robots and Systems, IEEE/RSJ International Conference on, volume 1, page , [2] Y. Bailly and Y. Amirat. Modeling and control of a hybrid continuum active catheter for aortic aneurysm treatment. In Robotics and Automation, ICRA Proceedings of the 2005 IEEE International Conference on, page , [3] G. Boccolato, F. Manta, D. Dumitru, and D. Cojocaru. 3D kinematics of a tentacle robot. NAUM International Journal of Mathematics and Computers Simulation, ISSN, 159:19232, [4] Ceilbot. The ceilbot project [5] Matthias Fueller, Juhana Leiwo, and Miguel Perez. Ceilbot - trunk manipulator - project plan autumn 2010, [6] B. A Jones, W. McMahan, and I. D. Walker. Design and analysis of a novel pneumatic manipulator. In Proceedings of 3rd IFAC Symposium on Mechatronic Systems, Sydney, Australia, page , [7] Bryan A. Jones and Ian D. Walker. Practical kinematics for Real-Time implementation of continuum robots. IEEE Transactions on Robotics, 22(6): , [8] W. McMahan, V. Chitrakaran, M. Csencsits, D. Dawson, I. D. Walker, B. A. Jones, M. Pritts, D. Dienno, M. Grissom, and C. D. Rahn. Field trials and testing of the OctArm continuum manipulator [9] W. McMahan, B. A Jones, and I. D Walker. Design and implementation of a multi-section continuum robot: Air-Octor. In Intelligent Robots and Systems, 2005.(IROS 2005) IEEE/RSJ International Conference on, page , [10] S. Neppalli and B. A Jones. Design, construction, and analysis of a continuum robot. In Proceedings of the International Conference on Intelligent Robots and Systems, pages , [11] G. Robinson and J. B. C. Davies. Continuum robots-a state of the art. In Robotics and Automation, Proceedings IEEE International Conference on Robotics and Automation, volume 4, page ,

9 [12] Ian Walker and Michael Hannan. A novel elephant s trunk robot. Atlanta, USA,

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