# US 4,369,402 A · Motion damping apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,369,402 A - Document ID: US4369402A - Status: Granted - Kind: A - Application number: 06/171,201 - Filed: 1980-07-22 - Granted: 1983-01-18 - Earliest claimed: 1980-07-22 - Assignees: Xerox Corporation - Inventors: Andrew Gabor; John C. G. Dunfield - Web page: https://patentgrep.com/patent/US4369402A ## CPC - B41J 1/24: the plane of the type or die face being perpendicular to the axis of rotation (B41J1/60 takes precedence) - G05B 19/232: {with speed feedback only} - G05B 2219/34215: Microprocessor - G05B 2219/37313: Derive speed from position - G05B 2219/41326: Step motor - G05B 2219/42182: Memory is Rom for servo control - G05B 2219/43006: Acceleration, deceleration control - G05B 2219/43181: Reaching reference position by spiraling speed reference - G05B 2219/43194: Speed steps, switch over as function of position - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) ## Abstract Apparatus is disclosed for controlling the movement of a movable element to bring said movable element to rest at a desired stopping position. The apparatus comprises a multi-phase drive motor having a drive shaft coupled to the movable element for driving same, a plurality of electrically conductive coils mounted in position-displaced relationship about the shaft, and means coupled to the drive shaft and responsive to the selective energization of the coils by respective motor drive signals for causing the corresponding rotation of the drive shaft and movement of the movable element. A sensor is coupled to the drive shaft and is responsive to the rotation thereof for generating an electrical signal containing information indicative of the direction, speed and distance of movement of said movable element. Further, means are included for detecting from the distance information indicated by the electrical signal whether the movable element is within a predetermined distance of the desired stopping position. When it is, a controller controls the levels of the motor drive signals in dependence upon the direction information indicated by the electrical signal. ## Claims ### Claim 1 Apparatus for controlling the damping mode movement of a movable element to bring said movable element to rest at a desired stopping position, said apparatus comprising: a multi-phase drive motor having a drive shaft coupled to said movable element for driving same, a plurality of electrically conductive coils mounted in position-displaced relationship about said shaft, and means coupled to said drive shaft and responsive to the selective energization of said coils by respective motor drive signals for causing the corresponding rotation of said drive shaft and movement of said movable element; a sensor coupled to said drive shaft and responsive to the rotation thereof for generating an electrical signal containing information indicative of the direction, speed and distance of movement of said movable element; means for detecting from the distance information indicated by said electrical signal whether said movable element is within a predetermined distance of said desired stopping position; and damping control means for controlling the levels of said motor drive signals in dependence upon the direction information indicated by said electrical signal following detection of said movable element being within said predetermined distance of said desired stopping position. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein said damping control means comprises means for selectively turning on and off or reversing predetermined ones of said motor drive signals and thus corresponding motor coils in dependence upon the direction information indicated by said electrical signal. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein said motor and thus said movable element are brought to a final stop with the motor drive signals for two adjacent coils on. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the motor drive signals for said two adjacent motor coils are selectively turned on and off by said damping control means in dependence upon the direction information indicated by said electrical signal. ### Claim 5 (depends on 1, 4) The apparatus of claim 1 or claim 4, wherein said drive motor is a stepper motor. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein said stepper motor is a four-phase motor having four coils. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein said sensor comprises: an electrically conductive sensor coil mounted adjacent the drive shaft of said motor; flux producing means mounted adjacent said sensor coil for producing a path of normally substantially constant magnetic flux adjacent said coil; and flux varying means coupled to said drive shaft and responsive to the rotation of said drive shaft by said motor for varying the level of said magnetic flux adjacent said coil in dependence upon the direction, speed and distance of rotation of said drive shaft, whereby the resultant electromotive force induced in said sensor coil defines said electrical signal across said sensor coil. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein, at a constant velocity of movement of said movable element, said electrical signal is periodic with a peak amplitude and frequency proportional to the velocity of said movable element, has a polarity indicative of the direction of movement of said movable element, and has a period representative of a predetermined increment of movement of said movable element. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein said sensor comprises at least two sensor coils mounted adjacent the drive shaft of said motor. ### Claim 10 (depends on 9) The apparatus of claim 9, wherein said at least two sensor coils are aligned about said drive shaft with respective ones of said motor coils. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein two of said electrical signals are respectively generated by said at least two sensor coils, said two electrical signals being mutually electrically phase-displaced by 90.degree.. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein said two electrical signals are substantially sinusoidal waveforms. ### Claim 13 (depends on 12) The apparatus of claim 12, further comprising: means coupled to said sensor coils for generating four square-wave signals; and means responsive to the levels of said square-wave signals for controlling the levels of said motor drive signals.