Automated Wire Cutting and Stripping Machine

Hello and Thank You for Viewing this Project!

Adam Lueders, Chris Habowski, and Vanessa Penaloza

This is a project my team and I made as our final Capstone project. We are current sophomores studying Electromechanical Technology at Thaddeus Stevens of Technology. During our time there, we have been able to learn about mechanical and electrical design, fabrication, and application within industry. The goal of the Capstone is to be a cumulation of the skills we gained while in class and industry. For this project, we decided to automate the process of cutting and stripping wire.

For those who know, the process of cutting, stripping, and feruling wire in electric panels can become tedious, especially when running wire to PLCs. To solve this problem, at least cutting and stripping, we created a machine to automate the process. Now, this is not a new machine. There are plenty of examples out there ranging from hobby types to industrial standard designs, for example, the Scheulniger EcoStrip 9380. These two aspects combined was the inspiration for this machine. With these ideas in mind the machine should be able to do the following:

Project Goals:

• Pull, cut, and strip multiple gauges of wire (18 - 14 awg) off of a spool
• Cut wire at multiple lengths (min: 5 inches max: 5 feet)
• Metering of the wire
• Strip wire at multiple lengths (depending on ferrule)
• Allow user to control machine manually or automatically through HMI
• Be able to select the length of wire, length of the strip, and number of cut wires

Supplies and Materials:

On the attached document are the supplies and materials used to create the project. It is broken down into mechanical supplies, electrical components, and 3D printed parts. Their descriptions, hyperlinks, price per unit, and number of units used are included. However, how each part was used and or designed will be covered in a later step.

Design:

Now that we understand what the project is, what we want it to do, and what parts we have to make it happen; let's talk about the overall design. This can be broken down into three parts: the puller and ejector, wire straightener, and cutter.

Puller and Ejector:

First, would be the puller and ejector. Very similarly to the EcoStrip 9380, our puller and ejector use motor-controlled pinch rollers to pull the wire off of its spool and feed the rest of the machine. Both pinch roller assemblies are made up of multiple 3D printed and mechanical parts that were either designed or fabricated to work with each other. Springs, located at the either ends of the assemblies, are the main driving forces that pulls the rollers together giving them the "pinch" needed to pull the wire.

Even though the assemblies are the same, they are used to do different processes. The puller is used to pull and meter wire off of the spool and to feed rest cutter. The ejector on the other hand, is used to either eject cut wire from the machine or position the wire back into the cutter for back-stripping. These assemblies took the most time design and fabricate mainly due to them being the heart of the process.

Wire Straightener:

Second, is the wire straightener. Wire coming off a spool can be bent, possibly causing problems for the puller and ejector assemblies. To solve this problem, a wire straightener was made. Again, springs were used to pull the two parts of the wire straightener together, applying pressure to and straightening the wire.

Cutter:

Third is the cutter. Pretty self-explanatory, the cutter is used to cut and strip the wire. Its assembly was pulled off of a milling machine and is actuated by a NEMA 17 stepper motor and ball screw. For cutting, the cutter goes all the way through the insulation and stranded metal core, but for stripping only the insulation needs to be cut. When the insulation is cut, the puller or ejector then pulls on the wire, as the cutter blades stay in place, to expose the stranded core.

Electrical Design:

Let's talk about the electrical design. First, movement of the machine is driven by three stepper motors. One NEMA 23 high-torque motor for the puller, one for the ejector, and a NEMA 17 low-torque motor for the cutter. For this application, we need to be able to send pulse and direction signals from our Siemens PLC to control when and what motor are enabled, how many steps they need to take, and what direction those steps are being taken. To solve this problem we looked at similar applications of running stepper motors. We found that multiple electrical components were required.

Components:

• PLC: Used to program the operation of the machine including motor actuation, HMI setup and display for remote control, manual control, and automated control of the machine.
• Ethernet Switch: Multiple components are required to have continuous communication between them to update each other. To have this done seamlessly, an ethernet switch was used.
• HMI: Used as main interface between the machine and operator. Can select auto or man control of the machine, wire cut length, strip length, and number of wire cut. Communication over Ethernet cable between HMI and PLC used to control the machine.
• Stepper Motor Drivers: Used to control the stepper motors. It takes the outputs from the PLC (pulse and direction) as inputs and outputs electrical signals both coils within the stepper motors. 2k ohm resistors were used to lower the signal coming from the PLC.
• NEMA 23 Stepper Motors: Controlled by outputs from PLC and stepper motor drives. Used to actuate the puller and ejector assemblies to pull and meter the wire throughout the process
• NEMA 17 Stepper Motor: Controlled by outputs from PLC and stepper motor drivers. Used to actuate the cutter to cut and strip the wire. Stripping is done with both the cutter and one of the pinch roller assemblies.
• 15 Amp 24 VDC Power Supply: Used to convert 120 VAC from wall into 15 amp 24 VDC for the motor drivers and motors to run off of. This component was rated for control of all motors at the same time.
• Multi-Colored Terminal Blocks: Used to provided multiple types of electrical power and terminals to connect to. Main use for powering each component.
• 18 awg Black Wire: Used to connect components together for controlled voltage as well as supplying power to components. Wire labels were used and different colored wires would be suggested for future projects.

Electrical Schematic:

A schematic was made to show how the electrical components should be connected to have power as well as controlled voltage for motion control. This schematic was based off of prior research as well as component manuals. Both the schematic and information (pinouts and more) on the components are attached to this section.

Mechanical Design:

For the mechanical design we looked at making a frame, 3D printing parts, assembling components, and mounting motors and sub-assemblies. These tasks were done throughout the semester as we continually honed the design and look of the project.

Frame:

First, the frame is made out of 80-20 extrusions fastened together with t-nuts and machine bolts. We also included a bottom and sides to make the frame more rigid and to contain the components inside. The bottom was made of 1/2" hard white plastic while the walls were made of clear plexiglass. This was really the first step as it provided the foundation of the project.

3D Parts Printing and Sub-Assemblies:

Next are the sub-assemblies. This would include the puller, ejector, and wire straightener that we covered earlier. These components were either modeled and printed or bought and fabricated to meet our needs. Multiple iterations of 3D parts and long print times prevented some assemblies from progressing throughout the project, but final iterations of parts and designs were found in the end.

Specifically, the wire straightener needed to be able to move up and down linearly while being able to apply pressure to the wire to straighten. We attached t-nuts and bolts to the female part of the assembly that allowed for movement being guided by an 80-20 frame.

The puller and ejector were the most complex assemblies to make. They required multiple 3D and fabricated parts to be assembled and then mounted to the frame. Controllable free movement of the assemblies was by cutting guides in the front panel of plexiglass and the use of springs, enough force was created to grip the wire while being free enough to account for larger gauges. Overall, this was the heart and soul of the project and we needed to get it right.

Mounting:

The next part of the project was mounting. This included mounting the motors, cutter, puller, ejector, wire straightener, HMI, and guides. Most of these objects were placed on the front panel. Rigid couplings were also installed to connect the motors to the puller and ejector for easy power transmission. The HMI was installed on the front for easy viewing and for operator control of the machine. For the cutter, it was mounted close to the ejector to allow for easy transfer of wire while the bottom blade of the cutter was mounted onto the frame below the top actuating blade. The puller and ejector assemblies were placed on either side of the cutter and guides were installed to keep the wire moving in the correct orientation. Ultimately, the assembly took about a day to complete, but was the culmination of many iterations, failed prints, and revised designs.

Programming:

When programming this machine I wanted to control the movement of each motor, implement the types of control of the machine on the HMI (manual/automatic), and start selecting subroutines within the program based on the number of steps it would take to extrude a certain length of wire. To create solutions for these challenges, I started with setting technology objects within the program (each one relates to a motor), started controlling motors manually on the commissioning tab on the laptop, and finally created a program that allowed for manual/automatic control of each motor remotely through the HMI.

Setting Up Connection: To start off we need to configure the devices we are using within the program as well as the connection/communication between them. To do this, I first went to the "Add new device" tab on the project tree. I am using an S7-1200 CPU 1214C DC/DC/DC PLC for this project. Afterward, add my HMI to the program using the same method. I used a KTP-400 Basic Siemens HMI for this project. Connection should be made between all three devices using ethernet cables, using a network switch (CSM 1277 Simatic Network Switch) makes this process possible. Now that there is configuration and communication between the devices we can move on to the technology objects.

Technology Object Configuration: To setup a technology object, a pulse generator needs to be selcted. Go to properties under the plc device configuration and configure the pulse generator you want to use. There are three motors in this project, which required the use of three pulse generators.

On the project under your PLC, there is a tab called technology objects. This refers to any motion control object (i.e. stepper motors, servo motors, and more). Select "Add new object" and configure the devices using the pulse generator(s) that was selected before.

Commissioning Tab Manual Control: to control each motor manually you can head to the commissioning tab under the technology objects tab. Because I had the correct wiring in the machine and configuration settings within the program, I was able to run each motor manually. Noe that we had the motors moving manually, it was time to control the motor manually and automatically through the HMI.

Remote Manual and Automatic Control: Multiple motion control functions were used for this project. They controlled the type of movement, the number of steps taken, and what direction the steps are taken. They are listed below.

• MC_Power: Used to enable and or disable axes of motion (motors). Important first step when programming for this application.
• MC_MoveJog: Used to run a motor manually in different directions. For this project, I linked a button on the HMI to the MB used to power the function.
• MC_MoveRelative: This function can be used to move the motor(s) in any direction in a number of steps. Unlike MC_MoveAbsolute, this function moves a number of steps in whatever position it is in.

The program itself was really split into three sections based on the functions that were used. Enable section to enable and or disable the motors, a jog function for manual remote control, and finally move relative function for automatic control of the motors.

With the automatic control section, I was able to cascade each function off of one another. So function 1 tells the puller motor to move 1800 steps clockwise. I could configure the functions so that when 1800 steps were reached by the puller motor, I could actuate the ejector motor immediately after. This can then be expanded into autonomous control of the machine.

To be able to meter the wire some simple calculations were made. If we relate the number of steps per revolution of each motor to the circumference of the wheel being used, you can start to understand the relation between steps per inch. When applied to the Move_Relative functions, subroutines can be made to extrude a specific amount of wire to cut and strip. Our puller and ejector motors were set to 1600 steps/rev and our wheels had a circumference of 4.71 inches. When these are related we find that...

• 6" Extrusion: 1.27 revolutions 2038.22 steps
• 8" Extrusion: 1.70 revolutions 2717.62 steps
• 10" Extrusion: 2.12 revolutions 3397.03 steps
• 12" Extrusion: 2.54 revolutions 4076.43 steps

With all of these topics combined, we were able control each motor manually, automatically, and simultaneously. The HMI provided an easy interface between the user and machine and controlled motion was found.

Results and Lessons Learned:

At the end of the project, we were to create motion through our design, pull wire, and cut into insulation, but we did not succeed in all areas as we hoped. We ran into multiple issues with the framing/mounting of components, specifically the cutter, 3D printing iterations, as well as programming for automatic control. Both are covered indepth below.

Cutter Design: It is important to understand that the cutter actuator was taken from a hobby CNC milling machine, so its application in our machine did not meet our specifications. Specifically, the framing/mounting of the actuator we found to be too weak for the forces that were generated for our process. Next is the motor itself. It was a NEMA 17 low torque motor that proved to be too weak for the application as well. We tried to bolster the frame by adding cross members to the frame, but ultimately it did not meet our standards.

When we look back on our design and assembly we could have done a lot differently. This includes shortening the arm of the cutter to produce less torque on the system, having the cutter mounted the assembly directly to the 80-20 frame, using a higher torque rated motor, having a higher thread pitch on the linear actuator, or we could have changed the total design for a more compact package. Overall, we learned a lot about what goes into the design of the cutter.

3D Printing Iterations: Over the course of this project, we have developed multiple iterations for the 3D printed parts within our design. This is one of the many examples where we had to adjust part design to meet the overall design of the machine. For example, our bearing motor mount (part in puller and ejector assemblies) went through multiple iterations. We changed the overall size, location of spring loops, thickness and depth of the part, and more. We found that designing and iterating through these parts took up a lot of time that could have been used in other parts of this project. Ultimately, this process of iterating was something we could not rush.

Programming: Concerning programming, we had trouble running the motors manually and automatically through the HMI. We found the process of designing and making the program with Siemens software was harder than previously thought. Unfortunately, this meant we had to control the motors through the laptop for your final presentation (not a good show).

When looking back, multiple things could have been done differently. First of all, we could have used a different brand of PLC (i.e. Unitronics or ABB). Siemens has a lot of applications, but can be pretty involved and hard to navigate through the software. Second, we could have started working on the program earlier, giving us more time to work out the kinks. Unfortunately, we started working on it three-quarters of the way through the semester. Finally, we could have asked for more help. Sometimes a simple call for help can solve the problem.

Ultimately:

Ultimately we learned a lot about what it takes to design, research, fabricate, build, and troubleshoot a machine of this size and caliber. Ideas like project and time management were also touched upon during this process. Even though we did not get it to operate exactly the way we wanted it to, we learned a lot and these lessons learned will never be forgotten.