The Unitrol SOFT TOUCH system is a safety device designed to protect resistance welder operators from electrode pinch point injuries. It is a standalone system intended for installation on non-Unitrol 1Ø AC and MFDC (inverter) welding controls. The system replaces the existing weld solenoid valve and integrates with the welder's pneumatic and electrical systems to control electrode closing force and initiate the welding sequence only after safe contact is detected.
Function Description:
The core function of the SOFT TOUCH system is to ensure that the welding electrodes close with a low, safe force until continuity is detected between the electrodes, indicating contact with a conductive material. Only after this safe contact is established does the system allow the electrodes to apply high welding force and initiate the welding sequence. This prevents the application of high force if a non-conductive object (like an operator's hand) is between the electrodes.
When the welding control sends a HIGH voltage signal to the SOFT TOUCH detection board (terminal #9), the system first energizes the low force solenoid valve (SVL), causing the electrodes to close under low force. For 9181-34WB systems, this involves gravity force with low force bucking pressure (ADVANCE) to counterbalance ram dead weight. For 9181-34YB systems, low air pressure is applied to the forward port of the welder cylinder.
The system then monitors the voltage signal at terminals #4 and #5. If the voltage drops below a minimum value within a preset "maximum detect time," continuity is detected. At this point, the high force solenoid valve (SVH) is energized, applying high electrode pressure, and a relay (K4) closes to initiate the welding sequence through terminals #6 and #7.
If continuity is not detected within the maximum detect time, the low force solenoid valve (SVL) is de-energized, causing the electrodes to open. This prevents the application of high force when no conductive material is present.
Important Technical Specifications:
The SOFT TOUCH system is available in various models, each tailored to specific welder types and hardware configurations. Key distinctions include:
- Voltage: Models are available for 115VAC, 24VDC, and 24VAC operation.
- Welder Type: Configurations for 1Ø AC welders and MFDC (inverter) welders.
- Ram Type: "Heavy Weight" (W models) and "Light Weight/Rocker Arm" (Y models).
- Snubber: Includes a blue snubber cylinder for SCR contactors in 9181-34WB and 9181-34YB models. If an existing snubber is present, it should be removed.
- Solenoid Valve Voltage: The system's internal relays (K2 and K3) must match the solenoid voltage of the welding control (e.g., 115VAC or 24VDC).
- Maximum Detect Time: Configurable via a 4-position DIPswitch on the sensor board, allowing settings of 0.25, 0.5, 0.75, and 1 second. The total detect time is the sum of the pushed-down switches (e.g., 0.25 + 1 = 1.25 seconds). This time is critical for allowing electrodes to close before a "Detect Time Exceeded" fault.
Usage Features:
- Pinch Point Safety: The primary feature is the prevention of high force application until safe contact is detected, significantly reducing the risk of pinch point injuries.
- Tip Dress Switch: A "Tip Dress" switch is provided on the annunciator panel. When activated, it closes the electrodes under low force, allowing for electrode maintenance or testing of the closing force without initiating a weld.
- LED Indicators: The annunciator panel features several LEDs to indicate system status:
- SYSTEM READY: Solid green when ready for operation. Flashing indicates a fault.
- Start: Lights when the weld control sends a start signal.
- Low Force On: Lights when the low force solenoid valve (SVL) is energized.
- Continuity Detected: Lights when continuity is detected between electrodes.
- High Force On: Lights when the high force solenoid valve (SVH) is energized.
- OK to Weld: Lights when the output relay closes to initiate the welding sequence.
- Detect Time Exceeded: Lights if continuity is not detected within the maximum detect time.
- Dress Electrodes: Lights in conjunction with "Detect Time Exceeded" if continuity is not detected.
- Continuity Detected with No Start Signal: Lights if continuity is detected without a start signal.
- Output Closed Fault: Lights if the output relay closes without a start signal.
- Retract Low Force On / Retract High Force On / Head Down Closed: (For optional retract systems) Indicate the status of the retract cylinder and associated forces.
- Optional Retract Systems (9181-34JA, 9181-34JB): These options provide enhanced safety when using welders with retract-type cylinders.
- 9181-34JA: For welders with a 3-section foot switch where the RETRACT switch is the first level. Includes a PNP proximity switch to detect when the retract cylinder is fully bottomed in the WORK position.
- 9181-34JB: For welders with a separate RETRACT foot switch or a RETRACT VOLTAGE from the welding control. This option is not for welders using a common weld and retract foot switch.
- Optional Timed Bypass (9181-34BPA): For welding materials with coatings or conditions that prevent good continuity. This option allows the welder to operate using TIMING instead of CONTINUITY to switch from low force to high welding force. The low force is applied for the time set on the DETECT TIME DIPswitch, after which high force is applied regardless of continuity. A key selector switch on the faceplate allows selection between CONTINUITY and TIMED DELAY modes. Caution: In TIMED mode, high force will apply even if a non-conductive material is between electrodes.
Maintenance Features:
- Troubleshooting Chart: A detailed chart helps diagnose issues based on LED indicators and system behavior (e.g., "Start LED not on solid," "Start LED flashing slowly," "Continuity Detected with No Start Signal").
- Testing Electronic System: A procedure for verifying system functionality, including closing electrodes with the TIP DRESS switch and checking for "Continuity Detected" and "Start Signal" LEDs.
- Adjusting Soft Touch Valves: Specific instructions are provided for adjusting the pneumatic system for both heavy weight (9181-34WB series) and light weight/rocker arm (9181-34YB series) welders. This involves setting ADVANCE PRESSURE, RETURN PRESSURE, and using the TIP DRESS switch to check electrode closing force.
- Testing Electrode Closing Force: Two methods are described for verifying the safe low closing force (under 50 pounds):
- Using a precise tip force measuring instrument (e.g., Tuffaloy model 601-3000DLC).
- Placing a wood pencil between electrodes; the electrodes should not dent the pencil more than 1/32" into either side.
- Wiring Control Cable Wiring Chart: Comprehensive table detailing wire color, TS6 terminal, and corresponding connections for both 24VDC and 115VAC models, emphasizing the critical connection of the orange wire to the weld solenoid valve driver output.
- Warranty: A 5-year limited warranty is provided, with coverage decreasing over time. Exclusions include unauthorized repairs, freight costs, field service labor, misuse, physical damage, and use contrary to specifications.
The Unitrol SOFT TOUCH system is a robust safety upgrade for resistance welders, designed for ease of installation and maintenance, with clear indicators and troubleshooting guidance to ensure safe and efficient operation.
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