1、_6$(7HFKQLFDO6WDQGDUGV%RDUG5XOHVSURYLGHWKDW7KLVUHSRUWLVSX EOLVKHGE6$(WRDGYDQFHWKHVWDWHRIWHFKQLFDO and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, LVWKHVROHUHVSRQ
2、VLELOLWRIWKHXVHUSAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions.Copyright 2017 SAE InternationalAll rights reserved. No part of this publication may be reproduced, sto
3、red in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE.TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada)Tel: +1 724-776-4970 (outside USA)Fax: 724-776-0790Ema
4、il: CustomerServicesae.orgSAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on thisTechnical Report, please visithttp:/standards.sae.org/ARP5777AEROSPACERECOMMENDED PRACTICEARP5777Issued 2010-05Reaffirmed 2017-02Maintenance and Inspection Procedures for Acme Screw Assembli
5、esRATIONALEARP5777 has been reaffirmed to comply with the SAE five-year review policy.1. SCOPE This document is to be used as a guide in preparing specifications for maintenance and inspection of acme screw assemblies used in driven linear actuators. It is intended to cover Acme screw assemblies dri
6、ven by electric, hydraulic, pneumatic, manual means, with or without gear case or speed reduction systems, and micro actuators.Though the Acme screw is the most common thread form for sliding contact jackscrews this guideline is equally applicable to other sliding contact thread forms such as buttre
7、ss, square, stub acme, and others including custom thread forms. The term Acme shall be used generally to address all sliding contact thread forms. 1.1 Purpose This document establishes guidelines and general procedures for inspection and maintenance of Acme screw assemblies for actuators intended f
8、or use in applications to position control surfaces in response to manual or automatic power control system inputs. 1.2 Background Previous service history has shown that inadequate lubrication causes accelerated wear of Acme screw assemblies. Inadequate lubrication has occurred as a result of diffi
9、culty in achieving proper lubrication by maintainers and long lubrication intervals. Wear problems have been compounded by long inspection intervals and variability in inspection results. 2. REFERENCES 2.1 Applicable References The following publications form a part of this document to the extent sp
10、ecified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precede
11、nce. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (out
12、side USA), www.sae.org.ARP4386 Terminology and Definitions for Aerospace Fluid Power, Actuation and Control Technologies 2.1.2 U.S. Government Publications Available from the Document Automation and Production Service (DAPS), Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-69
13、7-6257, http:/assist.daps.dla.mil/quicksearch/.MIL-HDBK-838 Lubrication of Military Equipment 2.2 Definitions ACME SCREW ASSEMBLIES: Mechanical transformers capable of converting rotary shaft input to linear travel of the output component. These actuators are configured to primarily transmit axial l
14、oad but may also be designed to support some amount of transverse (side) loads. SLIDING CONTACT SCREW: A screw utilizing a sliding contact such as Acme screws, square threads, buttress threads, standard 60 degree threads and others. These screws may also be referred to as lead screws, power screws,
15、Acme screws, etc. JACKSCREW: A generic name associated with any form of screw, rolling contact or sliding contact, which converts rotary motion into linear motion. SHALL: Denotes a requirement that must be met and verified by test. WILL: Denotes a requirement that must be met but need not be verifie
16、d by test. SHOULD: Denotes a requirement that is desired to be met, but which may be violated if necessary. MAY: Denotes a requirement that is optional to meet. NOTE: Each of these definitions may be redefined by the specification writer to meet the specific needs of a given system. Other terms may
17、also be used. NOTE: Refer to ARP4386 for the general terms that are used in the Aerospace Recommended Practice. 2.3 Abbreviations Use of ARP4386 is recommended for interpretation of commonly used abbreviations. 2.4 Acronyms All acronyms used should be listed and defined in the detail specification.
18、SAE INTERNATIONAL ARP5777 Page 2 of 7_3. REQUIREMENTS 3.1 Configurations The Acme screw assembly serves as the output device for a mechanical actuation system. A typical actuation system may contain one or more of the following components: a. Prime Mover (Hydraulic, Pneumatic, Electric) b. Connectin
19、g Members (Torque Shafts, Angle Gear Boxes, Couplings, U-Joints, Gearing) c. Safety Devices (No-Backs, Torque Limiters, Brakes) d. Sensors (RVTs, RVDTs, Tachometers, Hall Effects, Encoders, Limit Switches) e. Miscellaneous Devices (Clutches, Sequencers, Accessory Drives, etc.) These components may b
20、e configured and specified apart from or integrated with the linear mechanical actuator assembly. The configuration of the actuation system is determined by the prime contractor and is dependant on the specific air vehicle application. 3.2 Maintainability 3.2.1 Maintainability Characteristics The ul
21、timate maintainability goal of the Acme screw assembly design is to minimize maintenance requirements over the useful life of the program. The minimization of maintenance does not necessarily eliminate the need for periodic inspection. Inspection intervals shall be determined during development and
22、in serviceAll attempts should be made, through detail specification definition, to minimize scheduled preventive maintenance/servicing, inspection and maintenance from the design. This would greatly reduce life cycle cost over the life of the program. It is in the design phase where Acme screw assem
23、bly maintenance features should be addressed to reduce life cycle repair costs. Factors such as complexity, accessibility, visibility, testability, simplicity and interchangeability should influence maintenance design. 3.2.2 Maintenance Concept When an Acme screw assembly requires maintenance, the s
24、pecification should state the desired maintenance and level of maintenance that will apply. All attempts should be made to mitigate requirements for maintenance labor hours, Aerospace Ground Equipment (AGE), personnel skills and technical publications/data. The level of maintenance should be classif
25、ied/defined as:a. Organizational Level or Flight Line, b. Intermediate or Hangar, and/or c. Depot/Repair Station. SAE INTERNATIONAL ARP5777 Page 3 of 7_3.2.3 Quantitative Maintainability Each applicable level of maintenance should specify a detailed mean/average to repair period stated in maintenanc
26、e man-hours, personnel skill level, and support equipment requirements. To assist in determining the maintenance specific quantitative and qualitative maintainability tasks. Analyses can be performed, which can consist of: a. Maintainability Modeling b. Maintainability Allocations c. Maintainability
27、 Predictions d. Failure Mode and Effects Analysis (FMEA) Maintainability Information e. Maintainability Analysis f. Maintainability Design Criteria The Maintainability Analysis requirements for a procuring activity can be a combination of two or more of the analysis approaches that best meet the Acm
28、e screw assembly maintainability design objectives. 3.2.4 Maintainability Verification Once maintainability requirements have been defined, verification requirements defined in the specification can be used to demonstrate and validate the Acme screw assembly maintenance features and repair times. Ve
29、rification should be conducted under the auspices of the: a. Maintainability Demonstration, and b. Testability Requirements. It is also recommended that maintenance of critical jackscrews (i.e. for pitch trim applications) be included in the safety analysis and certification documentation as a Certi
30、fication Maintenance Requirement (CMR). This places a more stringent requirement on operators to perform the maintenance. 3.2.5 Maintenance Validation Maintenance validation should be accomplished during qualification testing, if required. Lubrication intervals should be validated during qualificati
31、on testing. Doubling of lubrication intervals during test may be required by certification authorities to demonstrate robustness. 3.2.6 Ground Support Equipment As a goal Ground Support Equipment (Special Tools) should not be required for the Organizational/Flight Line and Intermediate/Hangar levels
32、 of maintenance. Ground Support Equipment may be required for the Depot Level/Repair Station for complete teardown, inspection, repair and functional check. SAE INTERNATIONAL ARP5777 Page 4 of 7_3.3 Acme Screw Assembly Inspection and Maintenance Procedures 3.3.1 Inspection Inspection of all of the s
33、crew components should follow Component Maintenance Manual (CMM) guidelines. At a minimum these should include, but not be limited to, a backlash measurement, a check of the grease or lubrication and a visual check of all components. 3.3.1.1 Backlash (Free play) Because an Acme screw assembly is a s
34、liding contact device and subject to wear it is critical that the screw to nut end play be measured as a stand alone item and not in combination with other sources of free play. The Acme screw assembly overall backlash should be performed before cleaning and applying grease and may be determined as
35、follows. Lock the rotation of the input shaft or Acme screw itself. Measuring instruments should read relative axial movement between the fixed input and movable output member. Apply a set axial load in one direction, hold, and zero the measuring instrument. This set load must be collinear with the
36、axis of the output member. Apply the same set load in the opposite direction, hold and record the free play. The magnitude of the set load need only be large enough to “seat” all free components for an accurate measurement. This backlash check should be performed in several areas along the traveled
37、portion of the screw, preferably at both extreme ends of the used travel on the screw, and at a point in the middle. If a frequently used section of the screw is known or through observation, a backlash check should also be performed in that area. 3.3.1.1.1 General Note on End Play Checks In some sy
38、stems the static load applied to the output member can be relatively high; the load values applied to the actuator must be sufficient to overcome any surface static load and allow components in the load path to be seated in each load direction during measurement. If these loads are too high to devel
39、op a reasonable test procedure then an alternate approach could be to fix the surface with rig pins or blocks and measure the input shaft rotational free play at a set value of input torque in each direction. The effective end play can be calculated from the screw lead. This method is less accurate
40、than direct measurement so should only be used when other methods are impractical. 3.3.1.2 Visual check of Lubrication A visual check of the lubrication should be performed for amount and condition. Lubricant should be wet and show presence throughout the travelled portion of the Acme screw assembly
41、. Blackened, dark, or dried lubrication would indicate possible nut/screw abnormalities. Check for debris and/or particulate matter in the lubricant. For a more definitive check, grease samples can be analyzed to determine if grease has been exposed to contamination. 3.3.1.3 Visual check of Acme scr
42、ew assembly A visual check of the Acme screw assembly should be performed for any abnormalities. Ample lubricant should be present and any signs of material discoloration should be noted. Lubrication should be removed from the exposed portion of the screw. Attention should be focused on the screw th
43、read flanks for nicks, gouges, pitting, discoloration due to heat and any signs of galling, or excessive wear. The presence of any metallic particles in the used grease removed from a shaft is cause for further detailed inspection. SAE INTERNATIONAL ARP5777 Page 5 of 7_3.3.1.4 Wear/Degradation The s
44、crew shaft and mating components should be monitored for wear. Size and thread form should be routinely gauged to insure wear limits are not exceeded. Refer to manufacturers CMM for thread data. Thread forms may or may not adhere to published standards for acme threads. Thread profiles may take spec
45、ialty forms. Nut may be removed from screw shaft and gauged accordingly. Check for signs of uneven wear which may indicate misalignment in the actuator assembly. Components should be cleaned of all grease and contaminants and inspected for any signs of distress including, but not limited to scuffing
46、, pitting, lockup, galling, and/or seizure. Wear rate should be considered in determining the inspection and service requirements intervals. Record and track freeplay to determine if wear is increasing and the inspection interval should be decreased. Ensure that inspection interval has been approved
47、 by the appropriate agency. Acme screw journals should be inspected for signs of damage and wear. Size limits should be within OEM specifications found in the CMM. Repair of excessively worn journals should be made per CMM recommendations. Nicks, burrs, or raised edges should be smoothed and repaired. Cause of such defects should be investigated for other defective components.3.3.1.5 Redundant Load Path Requirements Within Output Member Any redundancies in loa
