Material testing machine having a control system for feedback-controlling the operation of a servo system

A material testing machine for measuring a mechanical property of a test piece based on a load given to the test piece and a mechanical change generated in the test piece, while feedback-controlling an operation of a servo system including a hydraulic actuator which gives the load to the test piece by means of a controller such that an actual load applied to the test piece coincides with a target load, comprising:

• load maintaining means for maintaining load observed at a time when a minute change in the test piece is detected while applying a gradually increasing load prior to material testing;
• estimating means for estimating a mechanical property of the test piece based on the actual load and the mechanical change of the test piece respectively detected after a displacement of the test piece is stabilized while the load observed when the minute change in the test piece was detected is maintained;
• initial gain setting means for setting an initial value of the control gain for the feedback control in accordance with the estimated mechanical property of the test piece;
• wherein said initial setting means sets the control gain at a minimum value of the control gain when giving of the load to the test piece is started prior to material testing, and thereafter the control gain is gradually increased with elapse of time;
• and
• the minute change in the test piece is detected when a mechanical change in the test piece beyond detecting resolution of a detector is detected.

A material testing machine for measuring a mechanical property of a test piece based on a load given to the test piece and a mechanical change generated in the test piece, while feedback-controlling an operation of a servo system including a hydraulic actuator which gives the load to the test piece by means of a controller such that an actual load applied to the test piece coincides with a target load, comprising:

• load maintaining means for maintaining load observed at a time when a minute change in the test piece is detected while applying a gradually increasing load prior to material testing;
• estimating means for estimating a mechanical property of the test piece based on the actual load and the mechanical change of the test piece respectively detected after a displacement of the test piece is stabilized while the load observed when the minute change in the test piece was detected is maintained;
• initial gain setting means for setting an initial value of the control gain for the feedback control in accordance with the estimated mechanical property of the test piece;
• and
• wherein said initial gain setting means searches a table in which the control gain is stored beforehand as a function of the mechanical property of the test piece, to thereby set the initial value of the control gain based on the mechanical property estimated by said estimating means.

A material testing machine for measuring a mechanical property of a test piece based on a load given to the test piece and a mechanical change generated in the test piece, while feedback-controlling an operation of a servo system including a hydraulic actuator which gives the load to the test piece by means of a controller such that actual load applied to the test piece coincides with target load, comprising:

• a force control system including a controller for feedback-controlling the operation of the servo system based on an actual force applied to the test piece, the actual force serving as a controlled variable in the feedback control;
• a displacement control system including a controller for feedback-controlling the operation of the servo system based on an actual displacement of the test piece, the actual displacement serving as a controlled variable in the feedback control;
• and
• control system changeover means for selectively operating either said force control system or said displacement control system, said control system changeover means making initial setting of a control output value to be supplied from the controller in the post-changeover control system, based on a control output value supplied from the controller in the pre-changeover control system to the servo system just before the changeover, and then making the control system changeover.