Allen-Bradley Using the 1756-MO2AE with the AEC (Cat. No. 4100-2.7) Application Note
Important User Information Because of the variety of uses for the products described in this publication, those responsible for the application and use of this control equipment must satisfy themselves that all necessary steps have been taken to assure that each application and use meets all performance and safety requirements, including any applicable laws, regulations, codes and standards. The illustrations, charts, sample programs and layout examples shown in this guide are intended solely for purposes of example. Since there are many variables and requirements associated with any particular installation, Allen-Bradley does not assume responsibility or liability (to include intellectual property liability) for actual use based upon the examples shown in this publication. Allen-Bradley publication SGI-1.1, Safety Guidelines for the Application, Installation, and Maintenance of Solid-State Control (available from your local Allen-Bradley office), describes some important differences between solid-state equipment and electromechanical devices that should be taken into consideration when applying products such as those described in this publication. Reproduction of the contents of this copyrighted publication, in whole or in part, without written permission of Allen-Bradley Company, Inc., is prohibited. Throughout this manual we use notes to make you aware of safety considerations.! ATTENTION: Identifies information about practices or circumstances that can lead to personal injury or death, property damage or economic loss. Attention statements help you to: identify a hazard avoid the hazard recognize the consequences Important: Identifies information that is critical for successful application and understanding of the product. GML, ULTRA, IMC, SCAN bus, Flex I/O, DTAM, PanelView, and SLC are trademarks; PLC is a registered trademark of Allen-Bradley Company, Inc.
Table of Contents i ControlLogix Servo Module AEC Module Purpose...1 Hardware Equipment used:...1 SSI Protocol...1 AEC Description...2 AEC Operation...2 Incremental Position Output:... 2 Absolute Strobe (Free Running Mode)...3 Absolute Strobe Timing...3 AEC Configuration...4 Setting the Rotary Switches...4 Configuration Switch A...5 Configuration Switch B...6 Encoder Configuration...6 Logix Processor / Servo Module / AEC Config...7 Design / Performance Considerations...7 What defines a Snappy low inertia servo loop?8 Mechanical Alignment / Absolute Zero...9 Aligning Axis / Homing On An Axis Configured For Linear Mode...10 Homing Anytime After Alignment...11 Aligning Axis / Homing On An Axis Configured For Rotary Mode...11 Home Sequence Rotary Axis...12 Home Sequence Linear Axis...12 Auto-Tuning the System...12 Ladder Program For Homing Sequence...13 Appendix A System Wiring System Wiring...18 System Wiring Diagram...19
ii Table of Contents
Application Note ControlLogix Servo Module AEC Module Using the M02AE servo module with the AEC to achieve absolute feedback Purpose The following note shows how to wire, configure, and program the 1756-M02AE servo module in a Contrologix system along with the 4100-AEC (Absolute Encoder Converter) to receive position feedback from a 842A Absolute Encoder (SSI) Hardware Equipment used: 1756-M02AE 1756-OB16I 4100-AEC 842A-31GB 4100-CCS15F 1394-SJT05-A 1326AB-B410G-21 1326-CCU-005 1326-CPB1-005 1394-AM03 845-FC-B-T Contrologix Servo Module DC Output Module (16 point Absolute Encoder Converter (Series B type for SSI) Multi-turn Absolute Encoder (36mm Pilot, 10mm Shaft, Grey Code, 4096 * 4096) Feedback cable/servo connection for interfacing AEC to Encoder 1394 Digital Servo Drive 1326 AB Servomotor 1326 Feedback/Commutation cable 1326 Power Cable 2Kw Axis Module Flexible Coupling for Encoder to Motor Housing 10mm (3/8 in) Note: A special coupling made to mate the encoder shaft and the 1326 Servo motor is required. Its part number is 845-FC-B-T. SSI Protocol Serial Synchronous Interface provides the position information via a serial data stream as opposed to the traditional parallel interface. Regardless of the resolution selected by the user, the encoder uses only four data and clock lines. The data transmission between the encoder and the SSI converter (AEC) is via a clock signal.
2 ControlLogix Servo Module AEC Module AEC Description The AEC is an absolute encoder converter. It receives the absolute position sent by the SSI transducer and changes it to an incremental quadrature signal that the motion controller can use. The AEC is designed to accept outputs from absolute encoders, linear displacement transducers, or any other measuring device, which transmits its measured values over an SSI. Several devices are supported with various combinations of counts per turn and number of turns. Parallel output devices are not supported. The AEC provides two independent channels of absolute to incremental quadrature conversion. The resolution of each channel is set via rotary switches and each one can operate with a transducer using a different supply voltage. (Although the supply voltages may be different, they are not isolated. The grounds must be of equal potential.) Each channel can be individually strobed to obtain new absolute or incremental position information. AEC Operation (Publication 4100-5.2 - March 1999) Absolute position information can be requested from the transducer via the AEC at any time. When the AEC interprets the strobe pulse train to be an absolute update request from the controlling hardware, it interrogates the transducer s absolute position and incrementally streams the position to the awaiting controller. Important: During an absolute position update, the quadrature encoder output stream is always positive: A leads B. Incremental Position Output: The AEC checks for the transducer position periodically. In the Locked mode of operation, this process is triggered and synchronized by the strobe input. In the Free-running mode of operation, the position is sampled, calculated, and transmitted every 1/1000 th of a second, based on the internal time of the AEC. The AEC compares the newly sampled absolute position against the last. It calculates the difference between the new and the old positions and transmits the difference through the encoder port in an incremental fashion. The position and direction information is encoded and sent using the industry standard (A and B) channels in quadrature (90 degree phasing). Each channel is driven differentially for improved noise immunity. When moving in the positive direction, the phase of the quadrature pulse train is A leading B. When moving in the negative direction, the phase of the quadrature pulse train is B leading A. The output frequency of both channels is fixed at 800kHz. One transducer position count is represented by one edge transition (either positive or negative) of the quadrature pulse train. This encoding scheme is defined as 4X. Your position controller must support the 4X decode of the AEC encoder output.
ControlLogix Servo Module AEC Module 3 Note: The 1756-MO2AE Servo Module does NOT have a built in STROBE pulse. Therefore, a program must be developed to strobe the encoder and return position. The AEC must run in Free Running Mode. Absolute Strobe (Free Running Mode) Absolute Strobe Timing This section defines the timing requirements for the two-strobe pulse train required for absolute position updates. The AEC must receive two strobe pulses to initiate and complete an absolute position update transfer. These are referred to as Ts1 and Ts2 in the data transfer protocol diagram. The following diagram and table outline the parametric requirements for an absolute position update cycle.
4 ControlLogix Servo Module AEC Module Parameter Locked Mode Free-Running Mode Min Max Min Max Tabs (absolute update cycle) = (Ts1s2 + Ts2 + Ts2hpe) 3001ms Ts1 (Strobe1 active pulse width) 100ms 1000ms 100ms 1000ms Ts2 (Strobe2 active pulse width) 5ms 1000ms 5ms 1000ms Ts1s2 (time from Strobe1 inactive to strobe2 active) Ts1+Ts1hpe+2 2000ms Ts1+Ts1hpe+2 2000ms Tph (time from Strobe1 inactive edge to encoder state hold) 30ms 30ms Ts1hpe (time from Strobe1 inactive to end of encoder stream) 0 25ms 0 25ms Ts2hpe (time from Strobe2 inactive to end of encoder stream) 0 1ms 0 1ms Tpei (*time from MSW pulse train end to incremental updating) 0 indefinite N/A N/A Thold N/A N/A 500ms 500ms *Operation mode dependent: Locked or Free-Running An absolute position request is an asynchronous event initiated by the controlling hardware. The first strobe starts the absolute position update cycle. The first strobe (Ts1) must be active for a minimum of 100ms, but for less than 1000ms to be valid. A strobe is sourcing input on the AEC. Internally, the AEC holds it high when inactive. To activate it, it must be connected and pulled low. Within 30ms (tph) of the strobe going active, the encoder output A and B signals are held at their current state (any incremental updating is prohibited). On Ts1 going inactive, the lower 16 bits of the absolute position is transmitted. Anywhere from 0 to 65535 counts can be transmitted. It can take up to 25ms (Ts1hpe) to transmit the least significant word (LSW) of the transducer position. After the LSW has been transmitted, the second strobe (Ts1s2) is brought active. When the second strobe goes inactive (ts2), it triggers the transmission of the most significant word (MSW). Anywhere from 0 to 511 counts can be transmitted. This completes an absolute position update cycle. Once the MSW has been sent (Tpei), the AEC begins sending incremental changes (Free-Running) or the Encoder output remains inactive as the AEC waits for an incremental strobe pulse (Locked). AEC Configuration Setting the Rotary Switches Setting the rotary switches located on the front panel, configures the AEC. Before you apply power to the AEC you must configure each axis to suit the transducer connected to it. A total of four parameters per axis must be configured. For each axis, determine the following;
ControlLogix Servo Module AEC Module 5 1. Transducer resolution in counts/turn (this is in counts/stroke for linear displacement transducers). Parameter 1 is set by configuration switch A. The table Configuration Switch A lists all the options supported by the AEC. Use this table to select the switch setting that matches the value for your transducer. Note: Configuration switch B is used for setting the next three parameters. You must find the setting that meets the combination of values for all three parameters. 2. Whether the transducer is a single or multi turn device. 3. Whether Grey or Binary is used for transducer data. 4. The operation mode. Locked or free running.! ATTENTION: The 1756-MO2AE controller must use the Free-running mode of operation. The Configuration Switch tables: Configuration Switch A Table 1: Transducer Resolutions Transducer Resolution Switch Setting Counts/Turn Bits/Turn 0 128 2 7 1 256 2 8 2 512 2 9 3 1024 2 10 4 2048 2 11 5 4096 2 12 6 8192 2 13 7 16384 2 14 8 32768 2 15 9 65536 2 16 A 131072 2 17 B 262144 2 18
6 ControlLogix Servo Module AEC Module Table 1: Transducer Resolutions Transducer Resolution C 2097152 2 21 D 4194304 2 22 E 16777216 2 24 F 33554432 2 25 Configuration Switch B Table 2: Transducer Turns, Data Format, & Operation Mode Transducer Turns, Data Format, & Operation Mode Switch Setting Turns Data Code Operation Mode 0 Single Grey Locked 1 Reserved for future use 2 Single Grey Free Run 3 Reserved for future use 4 Single Binary Locked 5 Reserved for future use 6 Single Binary Free Run 7 Reserved for future use 8 Multi Grey Locked 9 Reserved for future use A Multi Grey Free Run B Reserved for future use C Multi Binary Locked D Reserved for future use E Multi Binary Free Run F Reserved for future use If encoder noise faults occur on the marker channel tie the Z+ to 5V and Z- to common. Encoder Configuration Set the transducer resolution to match the AEC resolution. The absolute position preset defines a mechanical position to a zero point.
ControlLogix Servo Module AEC Module 7 Logix Processor / Servo Module / AEC Configuration The servo module (1756-MO2AE) must be configured for velocity loop operation. In this mode the servo module closes the position loop and the drive closes the velocity loop. When configuring the 1756-MO2AE with the AEC, set the AEC to the Free-running mode. In the Free-running mode the position is sampled, calculated, and transmitted at 1ms intervals, based on the internal time of the AEC. The AEC compares the newly sampled absolute position against the last and calculates the difference between the new and the old position. It then transmits the difference through the encoder port in an incremental fashion. Configure the servo module as follows: General: Type: Positioning Mode: Feedback: Homing: Servo: Position Only or Servo Linear or Rotary Counts / Unwind must be an integer Can t use Passive Homing Active Homing Immediate or Switch only any configuration except using a marker type configuration is acceptable (AEC doesn t support a marker channel at this time Velocity only Drive Fault Input should be used and set to Normally Closed this is what we use to tie into the e-stop string Note: The Drive OK contacts can be wired in series with the Drive Fault input as shown in the interconnect diagram. Design / Performance Considerations The overall system performance depends on the Drive / Motor / Mechanical configuration of your particular application. Some background information may help you understand how the system is designed and how this can affect the results. The 1756-MO2AE has velocity and position loop closure of 200 µs (fixed). The AEC transmits position at 1ms intervals. This is a 5:1 sampling difference. The result of this difference in sample rates may show up as rough or grainy operation of the motor. The smaller the inertia of the motor, the worse the effect.
8 ControlLogix Servo Module AEC Module With 200 µs servo updates in the Servo card and a non-synchronized 1ms AEC update (in free-running mode), you can have servo intervals which have fewer (or NONE) pulses of position data from the AEC. If that is the case, the snappy servo loop induces spikes to the motor, as it appears to be instantaneously stopping or severely slowing down, for some servo loops, when it is actually trying to run at a smooth constant speed. Larger ferrite motors do not experience this, except at very high speeds. However, it has been observed that Rare Earth motors at moderate speeds experience motor heating with small variations in speed. At high speeds Rare Earth motors have a very audible pinging with the resultant mechanical effects. What defines a Snappy low inertia servo loop? The dividing line for motor size appears to be; B410G motors and larger work fine. They will auto tune and produce smooth motion with no heating effects. For B330 motors and smaller, careful consideration needs to be given to each application. If you get poor system performance with these smaller motors, the servo module has a Output Filter feature that can enhance performance. This feature is similar to the Low Pass Filter in the 1394. The default setting for the Output Filter is 1 KHz. Our testing indicates that setting this filter to a value of 100Hz gives acceptable performance. Configure the DC Output module as follows:
ControlLogix Servo Module AEC Module 9 Wiring the DC Output Module to the Strobe Pulse DC Output Module (1756-OB16I/A) 1756-MO2AE 2 1 +OUT-0 +OUT-1 4 3 -OUT-0 -OUT-1 6 5 +ENABLE-0 +ENABLE-1 8 7 -ENABLE-0 -ENABLE-1 10 9 DRVFLT-0 DRVFLT-1 12 11 CHASSIS CHASSIS 14 13 IN_COM IN_COM 16 15 HOME-0 HOME-1 18 17 REG24V-0 REG24V-1 20 19 REG5V-0 REG5V-1 22 21 +OK -OK 24 23 CHASSIS CHASSIS 26 25 +CHA-0 +CHA-1 28 27 -CHA-0 -CHA-1 30 29 +CHB-0 +CHB-1 32 31 -CHB-0 -CHB-1 34 33 +CHZ-0 +CHZ-1 36 35 -CHZ-0 -CHZ-1 Strobe + (Yellow) 2 1 4 3 6 5 8 7 10 9 12 11 Strobe - (Black) 4100-CCS15F Axis 0 Encoder Connector AEC Reset Axis 0 Axis 1 Axis 1 Axis 0 A 10 98 2 1 B 3 7 2 6 1 8 4 7 3 6 2 5 1 A B A B 5 4 8 4 7 3 6 2 5 1 10 5 98 4 3 7 2 6 1 A B SSI Control Configuration Encoder Power Encoder Configuration Switches Switches SSI Control AEC 14 16 18 20 22 24 26 28 30 32 34 36 13 15 17 19 21 23 25 27 29 31 33 35 Refer to the wiring diagram and Pin tables in the Installation and Hook-Up chapter of the AEC Installation and Setup Manual for more information on wiring the AEC to the 1756-MO2AE and the DC Output Module (1756-OB16I/A). Mechanical Alignment / Absolute Zero The IMC-S Class products have an align absolute transducer feature, where the user moves the axis to a mechanical zero position, then enables the align absolute transducer function and the current axis location is called zero (ie: Actual_position = Command_Position = 0). Internal to the S-Class, any subsequent home function bases the absolute axis position received from the AEC card off of the zero determined in the align absolute transducer function.
10 ControlLogix Servo Module AEC Module The 1756-MO2AE does not have the align absolute feature. Therefore it requires some manual steps to achieve a similar result. It is important that you consider the following when aligning your axis: If the axis is NOT still when you align or home, the position information may be incorrect. The included RSLogix 5000 routine contains a homing sequence that disables feedback before strobing the AEC. If the axis is prone to drift, some sort of brake or clutch mechanism should be used to hold the axis stationary, or the position information may be incorrect. When you have mounted the encoder and are ready to define the travel limit (to reference the encoder to a known zero) press the button on the back of the encoder. The button is protected by a cap that can be removed with a screwdriver. Aligning Axis / Homing On An Axis Configured For Linear Mode The 842A SSI device has an absolute range of 4096 counts/rev * 4096 revs. The encoder is a rotary device. It can report unique position 0 <= position <= 4096 before repeating. This means that if you read 1 encoder count beyond 0, the value returned is 4095.999 repeating. This is why we need to align the axis. The following steps should be followed to align the axis. Remove all power to the system. Move the axis to the minimum physical travel position (ie: mechanical zero). Remove the coupling between the encoder and the motor. Apply power to the AEC. Zero the encoder by pressing the button on the back of the encoder. Physically turn the encoder shaft in the positive direction the number of rev s you want to have as a safe range (we used 5 rev s). Now, the axis is at the physical zero position and the encoder is offset to a safe travel distance. This position becomes our controller s zero. You also need to set the safe_travel_limit in the RSLogix program. The number is calculated by: (Number of rev s you turn encoder shaft) * (4096 cnts / rev) * (conversion constant) * (-1) In our case the safe_travel_limit was calculated by: (5 rev s) * (4096 cnts / rev) * (1) * (-1) = -20,480
Note: ControlLogix Servo Module AEC Module 11 The number is negative because of the * (-1). This is done because we moved the encoder shaft in the positive direction therefore, we need to make a relative position change in the opposite direction. Re-attach the encoder coupling to the motor. Be careful not to accidentally move the encoder shaft. Re-apply power to the system. Redefine this position to 0 (ie: redefine the actual_position to 0) by using the align axis rung in the ladder diagram. Homing Anytime After Alignment Whenever you issue a home sequence the home position you receive back must be offset backwards by the safe travel limit (ie: relative redefine of the actual_position safe travel limit). This returns a value that is indicative of where your axis is positioned. Important: Since you are using a safe travel limit, you shift the number of units from your total number of revolutions that your axis can travel. If you have 4096 rev s before you rollover, and your safe travel limit is 5, then you have a turns range of 5 to 4091. This is the valid position range that the controller can display. Aligning Axis / Homing On An Axis Configured For Rotary Mode Alignment in rotary mode is similar to the linear mode case. The 842A has a configurable amount of feedback counts vs. number of rev s before rollover. The factory default is 4096 counts/rev * 4096 revs. This configuration makes it a 4096 turn device. Important: In rotary mode, you MUST have an unwind constant counts/unwind that is a multiple of the number of turns (ie:4096 turns). This is because of cyclic compensation that a controller must take into account. Since we don t have a track of how many times the axis rolls over, we can t determine the correct rollover once the encoder reaches that point. To align the encoder in rotary mode: Remove all power to the system. Move the axis to the minimum physical travel position (ie: mechanical zero). Apply power to the AEC. Zero the encoder by pressing the button on the back of the encoder. Apply power back to the system.
12 ControlLogix Servo Module AEC Module Home Sequence Rotary Axis The home sequence gets the absolute position of the axis after the device has been aligned. It performs an absolute redefine of actual_position when completed. Home Sequence Linear Axis The home sequence for linear is the same as rotary, except for the redefine at the end of the sequence. The redefine has to be a relative type (actual position safe travel limit) Auto-Tuning the System Note: Refer to the Design / Performance section of this Application Note prior to tuning. The following steps are for auto-tuning higher inertia motors. 1. Refer to the tuning procedure for your particular drive. 2. Refer to the 1756-MO2AE tuning procedure and autotune the servo loop (position loop). If the axis is unstable, you may need to turn down the I gain in the drive, and re-tune the servo module. If you experience rough or grainy operation: 1. Repeat the above steps. If you experience instability, goto step 2. 2. Enable the Output Filter Bandwidth parameter from the axis gains page. Try different values for the filter number, 0 1000Hz. We found using 100Hz gives reasonable servo loop stability. Note: The output filter effects the system bandwidth. This may be a problem if you are running a high-speed application where you need the bandwidth. 3. Execute the auto-tune from the RSLogix menu. If this does not work, you may be unable to auto-tune your system. You may need to manually tune it.
Ladder Program (.acd file) For Homing Sequence ControlLogix Servo Module AEC Module 13 When you set home_sequence make sure feedback is off for the axis and wait for the axis to stop any free movement. Use the servo configuration bits to determine if the axis is set up as linear or rotary.
14 ControlLogix Servo Module AEC Module Turn the first strobe on (latch) and wait for the pulses to stop. (Tph on diagram). Redefine the position, this is used to clear out the Actual_position buffer. When redefine is done, wait for 300ms (Ts1).
ControlLogix Servo Module AEC Module 15 Turn the strobe off (end of Ts1) and wait for the encoder pulses to stop (Ts1hpe). Get the actual_position (the LSW word) and clear the actual_position buffer again for another read. Wait for the redefine position and set a dwell time between pulses.
16 ControlLogix Servo Module AEC Module Turn the second strobe pulse on and leave it on for 300ms (Ts2). Turn strobe off (Ts2) and wait for the pulses to stop (the MSW) and wait for 300ms. Store the actual_position (the MSW word) and use the two stored values to compute the absolute position. Redefine the axis to the absolute position determined by the previous rung. If the axis is configured as linear, you need to offset the position read back from the encoder. The value of this offset is the safe travel limit determined in the alignment procedure. If the axis is linear, offset the absolute position by the safe travel limit (shown in next rung.
ControlLogix Servo Module AEC Module 17 This rung is used after the alignment procedure, if it is a linear axis. Set the initial position to 0, then home each successive time.
Appendix A System Wiring The diagram on the following page shows the wiring for connecting a 1756-MO2AE, DC Output (1756-OB16I/A), a 1394, power supply, and an encoder to the AEC.
System Wiring 19 System Wiring Diagram DC Output 1756-OB16I/A 1756-MO2AE V Ref+ V Ref- Chassiss 1 3 11 A+ 25 A- 27 B+ 29 B- 31 Z+ 33 Z- 35 Enable+ 5 Enable- 7 Drive flt In. COM 9 13 Drive OK + 21 Drive OK - 22 Strobe+ Strobe- 1394-SJTXX-A A0 V REF+ A0 V REF- Chasis 24 V Enable 8 4 5 7 3 Power 2 1 Encoder Control +24V DC 24 V COM 4100-AEC Pin & Color on CCS15F A+ 4 White A- 10 Black B+ 5 Green B- 11 Black Z+ 6 Blue Z- 12 Black Strobe+ 2 Yellow Strobe-/COM 9 Black Shield 8 Black REF+ REF- Shield N/O Fault Relay N/O Fault Relay 1 Red 7 Black 8 Black 24 V DC Power Supply + COM Encoder 24 V Enable COM Contactor Enable Rest of 1394 start/stop string SSI 10 Clock + 5 Clock - 9 Data + 4 Data - 8 Shield 7 Transducer COM 6 Shield 1 Trans. +24V 2 Trans. + 15V 3 Trans. + 5V
20 System Wiring
Reach us now at www.rockwellautomation.com Wherever you need us, Rockwell Automation brings together leading brands in industrial automation including Allen-Bradley controls, Reliance Electric power transmission products, Dodge mechanical power transmission components, and Rockwell Software. Rockwell Automation's unique, flexible approach to helping customers achieve a competitive advantage is supported by thousands of authorized partners, distributors and system integrators around the world. Americas Headquarters, 1201 South Second Street, Milwaukee, WI 53204, USA, Tel: (1) 414 382-2000, Fax: (1) 414 382-4444 European Headquarters SA/NV, avenue Herrmann Debroux, 46, 1160 Brussels, Belgium, Tel: (32) 2 663 06 00, Fax: (32) 2 663 06 40 Asia Pacific Headquarters, 27/F Citicorp Centre, 18 Whitfield Road, Causeway Bay, Hong Kong, Tel: (852) 2887 4788, Fax: (852) 2508 1846 Publication 4100-2.7 March 1999 Copyright 1999 Allen-Bradley Company, Inc. Printed in USA