Sensor Body Fabrication

Overview

In this section, you'll 3D print the sensor body and the back cover. You'll also use a soldering iron to place a heat-set insert. The heat-set insert has threads on the inside. It will allow you to fasten the back cover to the sensor body using a screw later in the assembly process.

Materials

Step-by-Step Instructions

Changing the Adapter for a New Gripper

In the resources for this sensor we provide adapters for the Weiss Robotics WSG-50 gripper and the Franka Emika Panda Hand gripper. However, we have isolated the core sensor components from the gripper adapter so that it is possible to adapt the sensor to fit other robot grippers.

We have separated the body of the sensor into 3 individual parts that we unite in an assembly. These 3 components are the lens plate, electronics plate, and sensor adapter. These parts are shown below. To change the sensor for a different robot gripper, you only need to edit the sensor adapter. To generate a single printable component, combine all 3 parts into a single solid body.

Components of the GelSlim 4.0 sensor with the WSG-50 gripper adapter

There are several design tips we offer you when adapting this sensor to a new gripper:

Acquire a CAD model of the gripper if possible. This is useful to check alignment and design changes.
Identify where the zero-width position of the gripper is. We recommend that you design your gripper adapter such that the gel pads of the mounted sensors just touch at this zero-width position, as shown below. This way, the fingers can grasp small or thin objects. Make sure you consider the thickness of your gel pad when designing your gripper adapter. We provide design files for gel pads that are approximately 3mm thick.

The adapter is designed such that the 3mm gel pads are just touching when the gripper is in the zero-width position

Consider the thickness of the material for the gripper adapter. In order to be rigid, the sensor adapter should have enough material to prevent flexing at its connection point to the gripper.
Test prints of the mounting point can help you determine which tolerances are best suited for your printer and gripper. You can isolate just the mounting section of the adapter for a test print that should take under an hour to complete, but make sure that you print it in the same orientation you expect to print the full part.

Changing Sensor Thickness

Increasing the sensor thickness results in a stiffer sensor but restricts the grasp capability for some types of objects. Changing the sensor thickness to suit your application needs is easy by focusing on the sensor adapter. The thickness is determined by 2 sketches that define a plane. Material beyond the plane is removed. To change the thickness of the sensor, simply change the magnitude of the dimension in these 2 sketches, as shown below. Other modifications to the sensor thickening geometry can be designed to suit your application’s needs.

Left: Smaller magnitude of the highlighted dimension results in a thicker sensorRight: Larger magnitude of the highlighted dimension results in a thinner sensor

3D Print Sensor Body and Back Cover

Before you get started, download the sensor_body folder from the GelSlim 4.0 hardware repo on GitHub.

Make any desired changes to the lens plate, electronics plate, and sensor adapter then save the 3 parts into a single body
3D print the sensor body
Note: You want this component to be as stiff as possible so that the final sensor is quite rigid. There are many methods to accomplish this, such as increasing the infill percentage or changing the infill pattern.
3D print the back cover
Note: Printer default settings should be adequate for this print. This component isn't structural, so you can reduce infill to reduce print time.
Use flush cutters and tweezers to remove any support material from the components

Place Heat-Set Insert

Bring the ventilation system close to your work area and turn it on
Turn on the soldering iron to pre-heat
Place heat-set insert coarsely into the hole in the electronics plate, as shown below
Press the tip of the soldering iron into the heat-set insert and pivot to align the insert with the hole in the electronics plate, as shown below
Gently press the insert into the hole until the top of the insert is flush with the surface of the sensor body
Using tweezers, press down on the insert while retracting the soldering iron to keep the insert in the sensor body
Before the plastic cools (you will only have a few seconds), use the tweezers to make sure the heat-set insert is flush with the surface and that the hole is perpendicular to the surface
Turn off the soldering iron
Let the part cool for a few minutes

Use the hot soldering iron to align the heat-set insert with the hole. Press the insert into the hole until it's flush with the surface of the sensor body, then use tweezers to keep the insert in the sensor body while retracting the soldering iron.

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Next: Gel Mold Fabrication

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