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You are here:Home / Portfolio / Sewing machines / Engineered workplace / PFAFF 3791 PREMIUM


Docu seam system with needle feed and differentiable wheel feed and roller presser
 Auto-Interior / Car Interior
Säulen-Nähmaschine / Post bed sewing machineSchiebradtransport, angetriebener Rollfuß und mitgehende Nadel / Wheel feed, driven roller presser and needle feedVertikalgreifer, klein / Vertical hook, smallStichtyp Doppelsteppstich / stitch type lockstitchAnzahl der Nadeln / Number of needlesFadenanzahl / Number of theadsFadenabschneider / Thread trimmerVerrieglungs-Einrichtung / Backtracking systemRollfußautomatik / Automatic roller presser liftIntegrierte LED Leuchte / Integrated LED lightFadenspannungssteuerung / Thread tension controlSpulenfadenüberwachung über Sensor / Bobbin thread monitor via sensorUSB Anschluß / USB connectionTouchscreen / TouchscreenOption - Labeldrucker / Label PrinterOption - Oberfadenüberwachung über Kamera / Top Bobbin thread monitor via cameraOption - Spulenüberwachung über Kamera / Bobbin thread monitor via cameraOption - Labelkamera am Kopfdeckel / Label camera on the head coverOption - Handscanner / Hand scanner

Documented Quality - Stitch by Stitch

The POWERLINE 3721, 3741, 3745 and 3791 are quality assurance systems designed for use on safety-relevant seams. The PFAFF docu-sewing systems making an important contribution to extra driving safety. They monitor and guarantee perfect execution of the nominal breakage point on the reference seam from where the side airbag unfolds in the event of a serious incident. The seam must meet precisely stipulated parameters: on one hand it should not be too resistant as this will prevent the side airbag from expanding and unfolding; on the other hand the seam must have a minimum strength so that it does not tear open unexpected during normal use.

POWERLINE 3721, 3741, 3745 and 3791 machines significantly increase process safety and reliability. An essential benefit of these systems is to guarantee constant seam quality by identifying and sorting out unusable seams in real-time. This is important for product liability to counter and effectively refute any potential claims of recourse. The machines can be connected to the customer's ERP system - an important precondition especially in the automotive industry.

PFAFF docu-sewing systems are an important tool for quality assurance within the overall automotive production chain, even if it "just" deals with one simple element - an approx. 40 cm long seam section. Other possible fields of operation for the POWERLINE 3721, 3741, 3745 and 3791 are the production of parachutes, seatbelts, sails, awnings, tarpaulins - everything involving the production of safety relevant seams.

Mode of operation 3721/3741/3745/3791

The necessary critical values for the thread tension, stitch length and number of stitches are specified in the quality assurance system using test seams.

During the sewing process a sensor is monitoring in real-time the dynamic thread force ‘stitch by stitch’. On commissioning the system, an actuator automatically sets the thread tension (thread force) to the specified setpoint. If deviations are caused by external influences, the thread tension is automatically corrected (closed control circuit).

The configured stitch length and number of stitches are also monitored. The docu-system compares the measured values (stitch by stitch) with the previously entered thresholds and evaluates the seam quality. If the results are not within the specified tolerance area, a message is displayed (NOK = not ok). In the event of the above, the data is still stored but no label is printed.


  • Quality assurance system for the production of safety-relevant seams
  • In the field car interior the machine is very applicative for seams which have small radii at the formed parts
  • Automatical thread-tension device and real-time monitoring of thread force (stitch by stitch)
  • Skip stitch recognition inside and outside of documented seams
  • Electronic thread tension adjustment
  • Sewing head recognition
  • Operation of all functions with touch-screen
  • Free label design
  • Programmable stitch length and thread tension (in each seam sector)


  • Mechanic edge guide (swiveling) for recognition of docu seam start and docu seam end (tabs)
  • Ergonomic Pedal
  • Label printer
  • Stationary camera for printed label
  • Data base analysis tool
  • Calibration device

Calibration device

  • Easy handling of programs through touch screen
  • Installation of multiple docu-seams in one program possible
  • Hand scanner is reading and comparing process data, components and also user codes
  • Counting function for good and bad docu-seams
  • Thread force chart of single stitches
  • Monitoring function for signal analyzing and display of min./max. thread force
  • Static thread force rating for upper- and lower thread
  • Activate and/or locking of customer specific functions
  • On NOK seams – release through password possible
  • Easy reading, printing and saving of process parameters (SQL o. MS Access database)
  • 4 user levels (password protected)
  • Central database for multiple docu-seam machines
  • Easy communication between docu-seam system and database
  • User login through scanner
  • Later printing of label copies only possible through password
  • Bobbin thread monitor
  • Stationary camera for printed label

Unique service concept

Easy and quick access to all adjustments: The top arm cover and the face cover can be removed by loosening just a few screws.


Safety relevant seams on three-dimensional parts, e.g. impact absorbers of the steering wheel


Needle system: 134 PCL
Needle size: 80 - 100 Nm
Max. sewing speeds: 3.500 s.p.m
Max. stitch length: 7,0 mm
Max. thread size: 40/3
Stitch type: 301 (Lockstitch)
Clearance under the roller presser: max. 7,0 mm
Clear workspace: 345 x 275 mm
Connection voltage: single-phase a.c. 230 V, 50/60 Hz

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PFAFF is the exclusive trademark of VSM Group AB. | PFAFF Industriesysteme und Maschinen GmbH is an authorized licensee of the PFAFF trademark.
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