# US 4,743,823 A · Method and device for correcting backlash > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,743,823 A - Document ID: US4743823A - Status: Granted - Kind: A - Application number: 06/920,122 - Filed: 1986-10-17 - Granted: 1988-05-10 - Earliest claimed: 1985-10-17 - Assignees: Toshiba Machine Co., Ltd. - Inventors: Jun Fujita - Web page: https://patentgrep.com/patent/US4743823A ## CPC - G05B 19/404: characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia (G05B19/19, G05B19/41 take precedence) - G05B 19/291: {the positional error is used to control continuously the servomotor according to its magnitude} - G05B 2219/41036: Position error in memory, lookup table for correction actual position - G05B 2219/41041: Compensation pulses as function of direction movement - G05B 2219/41085: Compensation pulses on inversion of direction of rotation, movement - G05B 2219/41244: Dead band, zone - 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 A method and apparatus for correcting backlash are disclosed. The backlash width which may occur in the driving device is predetermined and one of the movable directions is selected as a reference moving direction. Further, the state where a movement is made in the reference direction, i.e. the state where the driving device and the driven member come into contact with each other and the positional relationship is unambiguously determined, is made to be a reference state. In this state, a position setting is made that a position detected by a position detector of an absolute position detector secured to the side of the driving means and a position of the driven member coincide with each other. When the operation is performed, a moving direction of an action carried out in response to a movement command immediately after power up is compared with the preset reference moving direction and if both directions do not coincide with each other an excessive movement by the value of the backlash width is made. Accordingly, the actual position of the driven member after the movement and the position detected by the output position detector always coincide with one another irrespective of the state before the power up. ## Claims ### Claim 1 A method of correcting a backlash serving as a principal cause of an error occurring between a position detected by an absolute position detector having a detecting portion provided on the side of a driving means and a position of a driven member moved by said driving means, comprising the steps of: storing a backlash width; storing a reference moving direction; issuing a movement command immediately after a power up; moving said driven member in response to said movement command a predetermined amount to a target position when the moving direction of said driven member coincides with a stored reference moving direction; and moving said driven member by an amount equal to the value of the backlash width in addition to the predetermined amount in response to said movement command when the moving direction is the reverse of the reference moving direction. ### Claim 2 (depends on 1) A method of correcting a backlash as set forth in claim 1, wherein each said step of moving said driven member comprises linearly moving the driven member. ### Claim 3 (depends on 1) A method of correcting a backlash as set forth in claim 1, further comprising the steps of storing a position detected by said absolute position detector and writing back said detected position to determine said target position of said driven member when a command to move said driven member in the reference moving direction is given to said driving means. ### Claim 4 (depends on 1) A method of correcting a backlash as set forth in claim 1, further comprising the step of determining said target position by comparing the moving direction of said movement command with the reference moving direction. ### Claim 5 A device for correcting a backlash serving as a principal cause of an error occurring between a position detected by an absolute position detector having a detecting portion provided on the side of a driving means and a position of a driven member moved by said driving means, comprising: means for storing said backlash width; means for storing a reference moving direction of said driven member; means for storing a detected position given by said absolute position detecting means; and means for writing back said detected position to determine a movement target position of said driven member when a command to move said driven member in the reference moving direction is given to said driving means, while, adding said backlash width to determine said movement target position when a command to move said driven member in a direction reverse to said reference moving direction is given to said driving means. ### Claim 6 (depends on 5) A device for correcting a backlash as set forth in claim 5, wherein said driven detection is rectilinearly movable.