Tailstock Control Device Servo Torque Compensation

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Solution Overview

Problem

Conventional electric tailstock systems using servo motors for machining support experience variations in thrust due to inertial forces and spring compression, leading to excessive thrust and instability during machining, especially when tailstock movement velocity changes.

Innovation Solution

A tailstock control device that calculates a limit torque value by subtracting excessive thrust caused by spring compression and inertial forces from the support thrust, and includes a unit to re-calculate the limit torque based on actual velocity detected when the output torque reaches the limit value, ensuring consistent support thrust.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the tailstock movement velocity is increased to improve productivity, then the tailstock can reach the workpiece faster, but the inertial forces and spring compression increase causing excessive thrust and instability

Engineering Contradiction:

Improvetailstock movement velocityVSAvoidsupport thrust stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The control device calculates the excessive thrust caused by inertial forces and spring compression in advance based on the movement velocity, and subtracts this calculated excessive thrust from the support thrust to determine the limit torque value. This preliminary calculation and compensation approach allows the system to maintain stable support thrust even at higher movement velocities, resolving the contradiction between productivity improvement and reliability maintenance.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If the limit torque value is calculated without considering spring compression and inertial forces, then the calculation is simpler, but the support thrust becomes excessive leading to workpiece deformation

Engineering Contradiction:

Improvecalculation complexityVSAvoidworkpiece dimensional accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The invention replaces complex mechanical thrust adjustment mechanisms with a computational approach. The control device uses calculations based on movement velocity to determine excessive thrust from spring compression and inertial forces, then subtracts this from the support thrust to establish the limit torque value. This substitution of mechanical adjustment with computational correction simplifies the overall system while improving precision, preventing workpiece deformation without adding mechanical complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If the tailstock feeding is stopped when torque reaches the limit value, then the support thrust can be controlled, but the tailstock continues to move due to inertial force causing excessive thrust

Engineering Contradiction:

Improvesupport thrust controlVSAvoidexcessive thrust during stopping

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The control device applies preliminary anti-action by calculating the excessive thrust that will occur during the stopping phase due to inertial forces and spring compression. This calculated excessive thrust is subtracted from the support thrust when determining the limit torque value. By anticipating and compensating for the excessive thrust before it occurs, the system maintains reliable support thrust control while preventing workpiece deformation during the stopping phase.

Inventive Principle:

Principle #9Preliminary anti-action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach stabilizes the support thrust, preventing workpiece protrusion or deformation due to insufficient or excessive pushing, resulting in a safer and more reliable tailstock control system.

Implementation Method 1

an excessive thrust calculating unit which calculates, as an excessive thrust, an excessive thrust due to an elastic restoring force caused by compression of the spring member during a period between the contact of the tailstock center moving in the tailstock movement velocity to the object to be machined and stopping of the tailstock center

Methodology Applied

Scientific EffectElastic restoring force: Elasticity

Implementation Method 2

a servo motor which drives a driving system of a tailstock having a spring member in forward and backward directions

Methodology Applied

Scientific EffectElectromagnetic torque: Electromagnetic Induction

Data Source

PatentUS8156850B2Tailstock control device

Publication Date: 2012.04.17 OKUMA CORP

AI summary

A tailstock control device supports an object to be machined by driving and controlling a servo motor which drives a driving system of a tailstock having a spring member in forward and backward directions, to cause a tailstock center connected to the tailstock to contact a center hole of the object to be machined. The tailstock control device comprises a limit torque value calculating unit which calculates, as a limit torque value (Tm), a drive torque value of the servo motor necessary for supporting the object to be machined, and a servo control unit which drives and controls the servo motor to attempt to move the tailstock at a tailstock movement velocity (Vs) which is set in advance, until an output torque value (Tr) of the servo motor reaches the limit torque value (Tm). The limit torque value (Tm) is calculated by subtracting, from the support thrust (Fa) necessary for supporting the object to be machined, an excessive thrust Fs which is calculated based on the tailstock movement velocity (Vs).