Configuring SINUMERIK 840D External Spindle on PROFIBUS

Overview

Integrating an external spindle drive with a SINUMERIK 840D powerline controller requires explicit configuration of the PROFIBUS DP link, the spindle's machine data axis image, and the PLC user program. When the spindle is a DC machine driven by a SIMOREG 6RA70 series converter, the 840D acts as the setpoint source and command issuer; the closed-loop speed/torque control is executed by the 6RA70's internal current and speed regulators. The 840D provides the command word, the speed setpoint, and reads back the actual speed and drive status via cyclic PROFIBUS DP telegrams (typically six PZD words per direction).

This reference covers the hardware topology, the 6RA70 PROFIBUS parameters, the relevant 840D machine data (MD), the PLC interface using the HLA / FC 18 / DB axis structure, and the path to display the spindle RPM on the HMI. A secondary path covering the 840Dsl with an ADI4 analog interface board (6FC5211-0BA01-0AA4, firmware 01.04.07) is also included for installations that need a non-PROFIBUS analog spindle.

System Architecture and PROFIBUS Topology

The classic 840D powerline spindle integration uses one of two layouts:

1. Direct PROFIBUS DP coupling – 840D NCU PROFIBUS interface → 6RA70 on the same DP segment. The drive appears as a PROFIdrive-compatible node and exchanges six PZD words cyclically.
2. ADI4 analog interface (840Dsl only) – ADI4 board in the NCU rack converts PROFIdrive telegrams to ±10 V analog setpoints for a non-PROFIBUS drive. Useful when the spindle drive does not support DP-V1/V2.

For both layouts the spindle encoder can be wired to either the drive (preferred for direct DC control) or to the NCU via the HLA module. If the encoder is wired to the drive, the 6RA70 closes the loop locally and the 840D reads back the smoothed actual value through PROFIBUS. If the encoder is wired to the NCU's HLA module, the NCU closes the loop and the 6RA70 operates as a torque follower; this is rarely the right choice for a DC spindle because it removes the 6RA70's speed loop stability advantage.

Hardware Configuration

Use the following minimum hardware list for a 840D powerline + 6RA70 external spindle:

6RA70 SIMOREG DC Master PROFIBUS Setup

Parameter setting on the 6RA70 side is split into drive-side parameters and PROFIBUS interface parameters. The two are linked by the PPO type selected in the master.

PROFIBUS interface parameters

PZD word mapping (PPO type 4)

Reference the Siemens Product Support SIMOREG 6RA70 parameter list (function block diagrams) for the bit definitions of STW1/ZSW1. Bits 0–3 of STW1 carry the standard PROFIdrive state machine (OFF1, OFF2, OFF3, ENABLE); bit 7 must be set for fault acknowledgement, and bit 10 must be set for control via PLC (control requested).

SINUMERIK 840D Machine Data Configuration

The 840D uses machine data to bind a logical spindle to a physical PROFIBUS slot and to choose between NCK-internal setpoint generation and external setpoint routing.

Key machine data

For PROFIBUS-coupled external drives on 840D, set MD30130 CTRLOUT_TYPE to 1 and reference the 6RA70 PROFIdrive PPO4 telegram in the drive configuration window. The drive slot index used here must match the logical address allocated by STEP 7 for the 6RA70 DP slave.

Spindle-specific MDs for rpm feedback to HMI

PLC Interface and Programming

The PLC exchanges cyclic data with the 6RA70 using the S7 input/output image. The 840D toolset provides function blocks in the standard toolbox (FC18, FC19, FC24, FC25) for spindle handling; the user typically only needs to route the VDI interface bits and handle the M3/M4/M5 logic in the PLC's spindle FC (default spindle FB in the supplied basic program).

Reading 6RA70 PZD into the PLC

STEP 7 hardware config maps the 6RA70 PPO4 to a logical address range. For a slave at PROFIBUS address 6 with PPO4, the typical I-address range is IB 264 .. IB 275 (6 PZD = 12 bytes) and the Q-address range is QB 264 .. QB 275. Adapt to the actual project; the following code assumes those addresses.

// Sample S7 STL excerpt – spindle control via PROFIBUS PPO4
// Drive slave address = 6, I address 264..275, Q address 264..275

// ---- Build STW1 (control word) ----
      L     QB 264                  // load current STW1 low byte
      L     W#16#0                  // clear working word
      T     LW 10

// Bit 0 = ON / OFF1
      A     M 100.0                 // PLC spindle enable (M3/M4 active)
      S     L 10.0
// Bit 1 = OFF2 (clear coast stop)
      R     L 10.1
// Bit 2 = OFF3 (rapid stop)
      R     L 10.2
// Bit 3 = Enable operation
      A     M 100.0
      S     L 10.3
// Bit 7 = Acknowledge fault
      A     M 102.0                 // fault acknowledge edge
      S     L 10.7
// Bit 10 = Control requested by PLC
      SET
      S     L 11.2                  // bit 10 of word = L 11.2
      L     LW 10
      T     QB 264                  // STW1 low  → drive

// ---- Build NSOLL (setpoint) ----
// M3/M4 direction via sign, magnitude from axis setpoint interface
      L     MD 104                  // signed setpoint RPM (e.g. 0.5 rpm units)
      ITD
      T     QD 266                  // PZD2 setpoint → drive

// ---- Read back actual speed from ZSW1/NIST ----
      L     IW 268                  // NIST actual speed
      T     MW 110                  // store in flag for HMI / DB

// ---- Read ZSW1 status ----
      L     IW 264                  // ZSW1 status word
      T     MW 112
// ZSW1 bit 2 – operation enabled
      A     M 112.2
      =     M 110.2                 // spindle running
// ZSW1 bit 3 – fault present
      A     M 112.3
      =     M 110.3                 // spindle fault → MMC alarm

VDI spindle interface (default NCK ↔ PLC bits)

ADI4 Module Alternative for 840Dsl

For 840Dsl systems that must drive an external spindle without PROFIBUS, the ADI4 (Analog Drive Interface for 4 axes) board converts PROFIdrive telegrams to ±10 V analog setpoints. The relevant catalog number is 6FC5211-0BA01-0AA4, firmware 01.04.07. The ADI4 mounts in the NCU rack and provides:

• 4 analog ±10 V setpoint outputs (one per axis / spindle).
• 4 incremental encoder inputs (TTL, RS422) for actual value acquisition.
• 4 SSI absolute encoder inputs (option).
• Digital I/O for drive enable and ready feedback.

Configuration steps for ADI4:

1. Set MD30100 CTRL_OUT_NR[ax] to the ADI4 channel (1..4).
2. Set MD30110 CTRLOUT_MODULE_NR[ax] to the ADI4 slot address (0 for ADI4 #1, 1 for ADI4 #2).
3. Set MD30130 CTRLOUT_TYPE[ax] = 0 (analog) and MD30240 ENC_TYPE[ax] = 1 (incremental).
4. Assign the encoder input via MD30220 ENC_MODULE_NR[ax] and MD30230 ENC_INPUT_NR[ax].
5. Wire the analog output (X11 of the ADI4) to the drive's setpoint input and the drive enable relay to one of the ADI4's digital outputs.

Check the ADI4 firmware against the NCU software version – a mismatch will surface as PROFIBUS alarm 380005 "PROFIBUS I/O fault". Up-to-date firmware is published on the Siemens support portal under entry ID 64932982 and related ADI4 KB articles.

Spindle Speed Monitoring

Per the SINUMERIK 840D sl / 828D Basic Functions manual (entry ID 64932982), the standard spindle monitoring functions include:

• Spindle in setpoint range (DB31..DBX84.5 / MD35400). The actual speed is within the tolerance band of the programmed S word. The check uses MD35150 SPIND_DES_VELO_TOL as the tolerance (default 0.1 = 10 %).
• Spindle in setpoint range (extended) (MD35410). Adds a programmable minimum and maximum speed window.
• Spindle in actual speed range (MD35500 SPIND_ON_SPEED_AT_IPO_START). Gates feed enable on the spindle actually being at S.
• Maximum spindle speed (MD35100 SPIND_VELO_LIMIT). Hard clamp independent of drive limits.
• Minimum / maximum gearbox speed (MD35120 / MD35130 SPIND_GEAR_MIN_VELO / MAX_VELO).

For an external 6RA70 spindle, also enable:

• MD36030 STANDSTILL_POS_TOL = 5° (spindle stop window for M5 / M0).
• MD36060 STANDSTILL_DELAY_TIME = 1.0 s (delay before "spindle stopped" flag is set).

HMI Display Configuration

To make the spindle RPM visible on the SINUMERIK Operate (or MMC 103) screen, follow these steps.

1. Open Start-up → Machine Data → Spindles in the operator area and select the spindle axis.
2. Set MD35020 SPIND_DEFAULT_ACT_SPEED = 1 – this switches the spindle display from programmed S to actual RPM.
3. For MMC 103 (HMI Advanced) screens, edit the file spindel.com / axisscreen.com in the project, or use the inbuilt axis screen configuration to show the actual speed field.
4. For SINUMERIK Operate, configure a custom user screen with the tag /Plc/DB31.DBD6 (current actual speed) or read the value the PLC has written into MW 110 from the PROFIBUS NIST word.

If the displayed value is the S-word value rather than the measured actual speed, verify that the encoder feedback path is correctly closed and that MD30240 ENC_TYPE matches the connected encoder (1 for incremental). A common mistake on retrofits is leaving the encoder on the NCU HLA module but wiring it for 6RA70 closed loop, which leaves the 840D with a default of 0 rpm.

Verification and Commissioning

1. Power the system and verify the 6RA70 appears online in STEP 7 hardware diagnostics (no SF/LED red).
2. Use the 6RA70 keypad parameter P790 to confirm PPO4 is selected and P786 to confirm the slave address matches the project.
3. In the HMI diagnostics, navigate to Startup → Diagnostics → PROFIBUS and confirm the 6RA70 reports a healthy cyclic PZD exchange.
4. From the PLC, force M 100.0 = 1 (spindle enable) and write a small speed setpoint (for example 10 % via MDW 104). Check the drive display shows a non-zero NSOLL and that the motor accelerates.
5. Measure the armature voltage and current with a clamp meter, compare to P401 (armature rated current) and P402 (armature rated voltage).
6. Verify HMI RPM tracks the actual motor speed within 5–10 RPM at 1000 rpm; if not, recalculate the encoder scaling in MD31020.
7. Trigger an E-Stop and confirm the drive honours OFF1/OFF2 (decay to 0 within 1 s) and that ZSW1 bit 3 is cleared by the drive and that the 840D issues alarm 25000 series.

Troubleshooting Matrix

Edge Cases and Field-Proven Caveats

• Multiple spindles on a single DP segment: the 840D reserves a PROFIBUS slot per logical drive. Two 6RA70 slaves with consecutive addresses (for example 6 and 7) use two slot configurations; keep the PPO type identical for both or the NCK will not link them.
• Power-on sequence: PROFIBUS must be live before the 6RA70 runs up its CBP2. If the 6RA70 powers up first it logs F060 (PROFIBUS timeout) which latches and prevents start until acknowledged.
• NCK reset after MD change: changes to MD30130, MD30220, MD30240 and MD35000 require an NCK reset. Plan a controlled restart window.
• Safety integration: when the spindle is part of a safety zone (Safety Integrated), the PROFIsafe telegram occupies PZD 7/8. Plan address space accordingly and use the Safety Integrated configuration tool, not the standard PPO4 selection.
• Mixed 611U and 6RA70 spindle: the 611U feed drives and the 6RA70 spindle can share the same DP segment. Reserve addresses 4/5 for 611U and 6 for 6RA70 to keep the bus scan deterministic.