Non-Contact Inductive Couplers Provide Wiring Advantages, Added Flexibility and Cost Savings Over Industrial Multi-Pin Connectors

Today, engineers are adding more and more sensors to in-die sensing packages in stamping applications. They do so to gain more information and diagnostics from their dies as well as reduce downtime. However, the increased number of sensors also increases the number of electric connections required in the automation system. Previously, the most common technique to accommodate large numbers of sensor in these stamping applications was with large, multi-pin connectors. (Figure 1)

Figure 1
Figure 1: A large multi-pin connector has been traditionally used in the past to add more electronics to a die.

The multi-pin connector approach works in these applications but can create issues, causing unplanned downtime. These problems include:

    1. Increased cost to the system, not only in the hardware itself, but in the wiring labor. Each pin of the connector must be individually wired based on the sensor configuration of each particular die. Depending on the sensor layout of the die, potentially each connector could need to be wired differently internally.
    2. A shorter life span for the multi-pin connector due to the tough stamping environment. The oil and lubrication fluids constantly spraying on the die can deteriorate the connectors plastic housings. Figure 1 shows the housing starting to come apart. When the connector is unplugged, these devices are not rated for IP67 and dirt, oil, and/or other debris can build up inside the connector.
    3. Cable damage during typical die change out. Occasionally, users forget to unplug the connectors before pulling the die out and they tear apart the device. If the connector is unplugged and left hanging off the die, it can be run over by a fork truck. Either way, new connectors are required to replace the damaged ones.
    4. Bent or damaged pins. Being mechanical in nature, the pin and contact points will wear out over time by regular plugging and unplugging of these devices.
    5. A lack of flexibility. If an additional sensor for the die is required, additional wiring is needed. The new sensor input needs to be wired to a free pin in the connector and a spare pin may not be available.
Figure 2
Figure 2: Above is a typical set up using these multi-pin connectors hard-wired to junction boxes.

Inductive couplers (non-contact) are another solution for in-die sensors connecting to an automation system. With inductive couplers, power and data are transferred across an air gap contact free. The system is made up of a base (transmitter) and remote (receiver) units. The base unit is typically mounted to the press itself and the remote unit to the die. As the die is set in place, the remote receives power from the base when aligned and exchanges data over a small air gap.

The remote and base units of an inductive coupler pair are fully encapsulated and typically rated IP67 (use like rated cabling). Because of this high ingress protection rating, the couplers are not affected by coolant, die lubricants, and/or debris in a typical stamping application. Being inherently non-contact, there is no mechanical wear and less unplanned downtime.

When selecting an inductive coupler, there are many considerations, including physical form factors (barrel or block styles) and functionality types (power only, input only, analog, configurable I/O, IO-Link, etc…). IO-Link inductive couplers offer the most flexibility as they allow 32 bytes of bi-direction data and power. With the large data size, there is a lot of room for future expansion of additional sensors.

Adding inductive couplers can be an easy way to save on unexpected downtime due to a bad connector.

fig 3
Figure 3: A typical layout of an IO-Link system using inductive couplers in a stamping application.

Error Proof Stamping Applications with Pressure Sensors

When improving product quality or production efficiency, manufacturing engineers typically turn to automation solutions to error proof and improve their application. In stamping applications, that often leads to adding sensors to help detect the presence of a material or a feature in a part being formed, for example, a hole in a part. In the stamping world, this can be referred to as “In-Die Sensing” or “Die Protection.” The term “Die Protection” is used because if the sensors do not see the material in the correct location when forming, then it could cause a die crash. The cost of a die crash can add up quickly. Not only is there lost production time, but also damage to the die that can be extremely costly to repair. Typically, several sensors are used throughout the die to look for material or features in the material at different locations, to make sure the material is present to protect the die. Manufacturing engineers tend to use photoelectric and/or inductive proximity sensors in these applications; however, pressure sensors are a cost-effective and straightforward alternative.

In today’s stamping applications, manufacturing engineers want to stamp parts faster while reducing downtime and scrap. One growing trend in press shops is the addition of nitrogen on the dies. By adding nitrogen-filled gas springs and/or nitrogen gas-filled lifters, the press can run faster and cycle parts through quicker.

Typically, the die is charged with nitrogen before the press starts running parts. Today, many stamping plants rely on an analog dial gauge (image 1) to determine if there is sufficient nitrogen pressure to operate safely. When a new die is set in the press, someone must look at the gauge and make sure it is correct before running the press. There is no type of signal or feedback from this gauge to the PLC or the press; therefore, no real error proofing method is in place to notify the operator if the pressure rating is correct or even present before starting the press. If the operator starts running the press without any nitrogen for the springs, then it will not cycle the material and can cause a crash.

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Another, likely more significant problem engineers face is a hole forming in one of the hoses while they are running. A very small hole in a hose may not be noticeable to the operator and may not even show up on the analog dial gauge. Without this feedback from the gauge, the press will continue to run and increase the likelihood that the parts will be stamped and be out of specification, causing unnecessary scrap. Scrap costs can be quite large and grow larger until the leak is discovered. Additionally, if the material cannot move through the press properly because of a lack of nitrogen pressure to the springs or lifters, it could cause material to back up and cause a crash.

By using a pressure sensor, you can set high and low pressure settings that will give an output when either of those is reached. The outputs can be discrete, analog, or IO-Link, and they can be tied to your PLC to trigger an alarm for the operator, send an alert to the HMI, or even stop the press. You can also have the PLC make sure pressure is present before starting the press to verify it was adequately charged with nitrogen during set up.

Adding an electronic pressure sensor to monitor the nitrogen pressure is a simple and cost-effective way to error proof this application and avoid costly problems.