Cable Based Parallel Robot for Outfitting of Drilling Modules

Introduction

In order to manufacture offshore drilling modules, various components of the construction must be mounted to the frame of the module. To solve this challenge, current methods utilize a series of pulleys and a lot of manual labor to move the parts into place.

It would be advantageous to develop a tool that can lift and maneuver the components in such a way that the process can be performed faster, cheaper, and safer.

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Drilling module

Concept Generation

Possible solutions are generated using a structured process involving problem decomposition, functional description, classification trees, and brainstorming. A functional description of the problem is shown in Figure 1.

Figure 1. Functional description

The functional description is used as a basis for research and systematic exploration of possible solutions.
Concept classification trees are made for each sub-function to explore the design space. For instance, the classification tree in Figure 2 is used to explore different ways to grasp the payload.

Figure 2: A classification tree that explores different ways to grasp a payload

The process results in a multitude of concepts. These are evaluated and reduced to seven main concepts for further investigation. Some of these are shown in Figure 3.

Concept Selection

Each concept is given ratings on how they perform according to a set of selection criteria. A cable based parallel robot as shown in Figure 4 is regarded as the most suitable concept.

Figure 4: Cable based parallel robot

System Design

The system is simulated in order to determine the load cycle of the actuators as shown in Figure 5.

Figure 5: Torque and speed requirements of the actuators

Kinematic equations of the system are also derived. This allow the user to control translational and rotational speed of the payload without having to think about the movement of each individual winch.

Figure 6: Inverse and forward kinematics

3D-models, electrical schematics, finite element analysis, and hand calculations are carried out to further develop the system. Emphasis is put on modularity and light weight components so that the system can be assembled and disassembled as needed.

Electrical System

The system is powered by a common 230 VAC supply/wall outlet. The AC power is tranformed into DC power by the circuit shown in figure 7. 

1. 230 VAC is stepped down to a lower voltage by a transformer (L1).
2. AC is converted into DC by a full wave diode bridge rectifier (D2, D3, D4, D5).
3. Capacitors C1 and C2  makes the output smoother.
4. Voltage regulator U1  fine tunes the voltage to the appropriate level.

Figure 7: AC to DC

A RoboClaw 2x30A  controller is connected to each pair of motors and encoders as shown in figure 8. A total of 3 controllers are needed for 6 motors. 

Figure 8: Motor controller, motors, encoders, power supply, and data transfer

Results

The resulting concept has a load capacity of at least 490 kg, and maximum movement speed of 3 cm/s.

Final design

Artist's rendition of the final product in use (with different actuator placement).