Igus-robotic-arm

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PMAC configuration 20-sim configuration =Igus robotic arm=

We are currently doing a project that is named "Igus robotic Arm". The main goal of this project is to develop a low-cost robotic arm that can be used in several different applications. The project is being done at Fontys University "Kenniscentrum Mechatronica".

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**Igus**
Igus is a German supplier for bearings and cable management systems and so on. Currently they're also producing parts for the realisation of robotic arms. Examples of these parts can be seen in figure 1 & 2. The joint in figure 1 has 2 degrees of freedom (DOF), pivoting and rotating. The joint in figure 2 has 1 degree of freedom, rotating.

The build of the system at Fontys can be seen in figure 3. 2 joints with 2 DOF and a shoulder joint is used. The total sums up to 5 DOF.
 * Rotating movement (DOF2 en DOF4) -> ±270 degrees from center
 * Total angle = 540 degrees -> 1,5 rotation
 * Pivoting movement (DOF1 en DOF3) -> ±90 degrees from center
 * Total angle = 180 degrees
 * Rotating movement shoulder joint (DOF5) -> ±90 degrees from center
 * Total angle = 180 degrees -> 0,5 rotation

Each DOF has an incremental encoder attached. The resolution for the pivoting and rotation is different:


 * Pivoting
 * 31 pole pairs
 * 40 pulses/polepair
 * 160 positions/polepair
 * 1240 pulses/revolution
 * 4960 positons/revolution
 * Roterende beweging
 * 29 pole pairs
 * 40 pulses/polepair
 * 160 positions/polepair
 * 1160 pulses/revolution
 * 4640 positions/revolution
 * Accuracy
 * Pivoting -> 360/4960 ≈ 0,0726 graad
 * Rotation -> 360/4640 ≈ 0,0776 graad

Information encoder

=media type="youtube" key="7LM82WT6Ma0" height="315" width="420"= See also: @http://www.igus.de/Blog_DE/category/robolink-blog.aspx

**Mechanical design**
The mechanical design is dependent from a few elements;
 * Tensioning wheel
 * Motors
 * Bearing
 * Coupling
 * Rope management

**Tensioning wheel**
For realising the movement of the joint it's necessary that the ropes can be driven. At the current setup this is done through drivewheels from Igus. The advantage of these wheels are: - ropes can be tensioned - drivewheel size equals joint size (easy math) The drivewheel can be seen in figure 4.

User manual tensioning wheel (German)

**Motors**
Maxon motors with Maxon Motor Controllers (4-q-dc) are used in the new assembly. The torque is an important aspect of these motors.

Because 2 different movements are made, it is important to look at the need torque and forces. At igus the following data is available:
 * Pivoting movement -> 12[Nm]** at force **600[N]** on the rope
 * Rotating movement -> 5[Nm]** at force **300[N]** on the rope

The diameter from the motor driving wheel equals the diameter in the joints, therefore:
 * Pivoting movement** -> 2*12[Nm] = 24[Nm]
 * Rotating movement** -> 2* 5[Nm] = 10[Nm]

The motor selection delivered the following;
 * Torque pivoting movement ±27,88[Nm]
 * Torque rotating movement ±15[Nm]



**Bearings**
Because the radial forces on the drive shaft are to high (max. radial forces exceed max. allowed radial forces gearbox), bearings are used. In this way the radial forces don't exceed the maximum allowed radial forces on the gearbox. The used bearings are of the type:6201-2Z & 6301-2Z: SKF 6001-2Z PDF SKF 6301-2Z PDF

**Coupling**
The output of the gearbox must be coupled to the drive shaft, therefore we fitted a coupling. This coupling has a high torsional stiffnes and it can handle a small misalignment. MCOCGWK38-12-12 product page

**Rope management**
The shoulder joint has a rope management system, in this way the ropes get seperated.

**Total concept**
All of the above is used in the total concept.







The drawings from the designed parts can be seen here:

Motion controller




20-sim
The possibility to implement the motion controller in 20-sim is currently investigated. The goal is to simulate the robotic arm and it's controller.

The Frequency Response Function from the motors be seen in figure 12 & 13.
 * FRF motors**

In 20-sim a torque actuator with an inertia and a damper is used to simulate the used motors.

**Sources**
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