FAQ: Is there a list of technical recommendations for safe guarding an MP940 Servo Control System against overspeed conditions?
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Yes, below is an example written up for an MP940 Indexing System with a Direct Drive Motor, but can also be applied to various other applications:
Product Description Ordering Part Number
Direct Drive Motor: SGMCS-2ZN***
Sigma II Amplifier: SGDH-30AE
MP940 Machine Controller: JEPMC-MC400
MotionWorks Software: MPE720
The Yaskawa 3kW Direct Drive Servo, SGDH Sigma II Servo Amplifier, MP940 Machine Controller, and MPE720 MotionWorks Software is a programmable system capable of operating the motor in various applications such as absolute rotary motion indexing. To insure that the system controls the motor in the way the machine designer expects, the system design specifics should be considered. Since the Yaskawa system is scalable, it allows the designer to add modules for increased ability and flexibility to suit the needs of various applications, including segmented variations of indexing applications. The description below describes some features of how each module monitors and handles speed concerns.
1) Motor: SGDH servo amplifier has a feature that will auto-id the SGMCS-2ZN direct drive motor through the serial encoder, and identify that it has a max speed of 250 rpm. If the encoder wire is unplugged, or if the serial communications data becomes compromised due to electrical noise, the system will automatically detect it, and fault out on an A.C* alarm. There is more information about these alarms in the manual or in our faq site, faq.yaskawa.com.
2) Amplifier: SGDH servo amplifier has a feature that will fault out on overspeed A.51 alarm if the motor exceeds 250 rpm by an amount. Alarm detection occurs within about 1msec of when the servo amplifier calculates that the speed has reached 20% above max speed. Once the alarm is detected, the amplifier faults out on overspeed, and annunciates the alarm. The motor will stop according to stop condition parameter settings (coast or dynamic brake, see Pn001).
- The alarm output of the SGDH amplifier should be wired in series with the E-Stop circuit to insure main power gets dropped out in the event of a Servo Amplifier Alarm. Refer to section 5.5.2 in the MP940 Design and Maintenance Users Manual, SIEZ-C887-4.1.
- The Servo Amplifier has a feature that allows the servo to be jogged regardless of the state of the controller, overriding the controller. This is available for startup and testing purposes, and ease of use. When the machine is commissioned for production, it is recommended that this feature as well as access to any parameter be locked out. SGDH Parameter access through the front panel can be locked out by setting Fn010=1. Refer to section 7.2.12 in Sigma II Servo User Manual, YEA-SIA-S800-32.2.
3) Controller: MP940 controls the servo amplifier via Dual Port Ram interface connection, and should be used to enable/disable the servo, as well as supply the control reference signal. This interface is completely digital, and handshakes communication on a watch dog timer. If the CPU faults out on a serious error it will cause a watch dog error, and the amplifier will automatically fault out on an A.E2 alarm, disabling the servo.
- It is recommended that all low power control signals be wired to the MP940 I/O connector with exception to the following which wire to the 1CN connector: Positive and Negative over travels inputs, Home Latch or Motor Position Latch input, and Pulse Generator output. All 1CN inputs can be used as programmable inputs monitored via register IWC025.
4) Software Setup: MPE720 MotionWorks software programming environment is used to setup, program, and monitor the MP940 and servo system. Fixed parameters and setup parameters are available for flexibility and assurance of control. Proper setup of these parameters as recommended in the users manual will insure the direct drive servo positions accurately and as expected. It is recommended that all adjustments to the setup and parameters be made from this software. OWC004/OWC005 are also available parameters that can be set to limit speed (refer to manual section 11.3, SIEZ-C887-4.1 position mode preparation info when motion command is used, see control mode block diagram 11.21).
- During software setup, its important to characterize a complete set of tuning gains for the mechanical system, first without the load, and finally with the load (Primarily parameters: Pn100, Pn101, Pn103, OWC010, OWC011, OWC035, and all low pass or notch filtering). See section 6.4.3 for a complete set of gain-related parameters. Taking measurements of torque and speed profile during a positioning move cycle, and recording this information is called 'servo gain baselining'. Documenting this is recommended for future reference when troubleshooting a system. Guidelines on Tuning can also be found in Example FAQs on faq.yaskawa.com: BFAR-5DHHXL, MTN-5WZJZ7.
- Any constant or variable values that are considered default parameter settings for the machine installation, should be hard coded into the Startup A drawing, so that the A drawing will store the hard coded values into the register which is used in the application program. This insures that all default values are stored in the program in the event that an MP940 controller is swapped out. Parameter set changes during machine operation can be set by downloading recipes from an HMI, or tweaked from the HMI.
5) Software Programming: There are several ways to program the system because of the variety of applications, including indexing. If the chosen method to position is by setting the Motion Command Code to positioning (OWC020=1), then the final position command should be conditioned and checked, then sent to the Command Register (OWC012). Good practice for coding in ladder would also include interlocking code to protect the overall control of the system such as: servo ready/fault check, over travel check, safety I/O check, speed command verification and limit checking, actual speed calculation check, etc.
- It is also recommended that a general purpose output be dedicated to interlock in series with the hardwired E-Stop circuit, preventing the E-Stop circuit from engaging main power until the MP940 code is running and controlling the output. If software safety check code detects abnormalities, it should set the output to off, causing dropout of E-Stop power. This is possible because the MP940 and SGDH amplifier control power is separate from the servomotor main power.
- In instances where load will be changing, changing gains on the fly should be considered. If the system is rigid enough, it may be possible to linearly scale the gains using Pn103, otherwise, gain relationships may need to be adjusted. This can be determined through testing.
- Software application code can be secured by password protecting through the user management section. Seven levels of read and write access protection are available.
6) Software Testing and Verification: Good practice for machine commissioning is to validate program functions through sign-off testing. This is often performed with the help of a checklist that shows columns for: Test item, verification test, acceptance criteria, and a place for the tester to sign and date.
7) Software Maintenance: Once the program and system has been tested, the application program should be baselined by assigning a production version, and should be backed up. In addition, the critical control software modules should be secured with password protection to support authorized changes only through an 'application software version control process'.
8) External Devices: HMI variable settings should be limited to insure the system does not operate as unexpected when the operator (or external device) enters set values outside of the expected range. If needed, an external speed monitor with independent circuitry could be connected, and hardwired to provide a final layer of independent overspeed protection.
9) System Level: Layered protection at each level (motor, amplifier, controller, setup, programming, testing, maintenance, external devices) will insure mitigation as well as contingency execution in the event that any particular safety element is compromised by mistake (example, if someone changes a programmable value accidentally, or by-passes a wired protection).
Ultimately each application is different, and demands a varying level of protection against anomalies based on a balance of safety requirement and feasibility of cost. These are all at the discretion of the installer. It should also be recognized that the operators or users of this machine may alter the system at any point based on the ease of access to bypass functions or features. For this reason, it is also recommended that lock-out tag-out hardware be installed on the control enclosure, as well as a maintenance safety procedure be written to support that. In any of these cases, the Direct Drive motor, SGDH amplifier, MP940 controller, and MPE720 software is designed to operate together, and if wired, installed, setup, programmed, and maintained in accordance to the respective product users manual, and utilizing best practices, the motor will position as expected.
Resources:
- MPE720 Software Users Manual# SIEPC88070005A
- MP940 Users Manual# SIEZ-C887-4.1
- Sigma II Users Manual# YEA-SIA-S800-32.2
- Sigma II Servo Tuning FAQ# BFAR-5DHHXL
- Tuning Tips for Direct Drive Servo FAQ# MTN-5WZJZ7
SAFETY PRECAUTIONS AND INSTRUCTIONS FOR USE OF FAQ INFORMATION!
Please read and understand the product instruction manual before installing, servicing or operating Yaskawa products. FAQ content and illustrations are provided as technical advice to augment the information in manual, not supersede it. It is not possible to give detailed instructions for all types of installation or support activities. The information described in the FAQs are subject to change without notice to improve the product or FAQ. Yaskawa assumes no responsibility for errors or omissions or damages resulting from the use of the information contained in any FAQ. All warnings, cautions and product instruction for product use must be followed. Installation, operation and maintenance should be carried out by qualified personnel. Failure to observe these and other precautions highlighted in the product manuals will expose the user to high voltages resulting in, serious injury or death. Qualified personnel are defined as individuals who are familiar with the installation, starting, operation and maintenance of Yaskawa products of the type described and have proper qualifications to perform the work.
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