Sewing machine

A sewing machine, comprising:

• a feed portion that is configured to feed a work cloth in a feed direction;
• a detection portion that is configured to detect ultrasonic waves;
• a processor;
• and
• a memory that is configured to store computer-readable instructions that, when executed by the processor, cause the processor to perform processes comprising:
• identifying a position of an ultrasonic wave transmission source as a first position, based on the ultrasonic waves that have been transmitted from the ultrasonic wave transmission source and detected by the detection portion, the ultrasonic wave transmission source being placed on the work cloth,
• calculating a first distance based on the first position, the first distance being a distance from a reference position to the first position,
• causing the feed portion to feed the work cloth in accordance with first data, the first data being data for feeding the work cloth over a second distance, the second distance being shorter than the first distance,
• identifying, after the feed portion has fed the work cloth in accordance with the first data, a position of the ultrasonic wave transmission source as a second position, based on the ultrasonic waves that have been transmitted from the ultrasonic wave transmission source and detected by the detection portion, the ultrasonic wave transmission source being placed on the work cloth, the second position being an equivalent of the first position after the work cloth has been fed,
• calculating a third distance based on the first distance and the second position, the third distance being an actual distance over which the work cloth has been fed,
• calculating a feed efficiency of the teed portion, based on the second distance and the third distance, the second distance being a distance had on the first data,
• correcting a fourth distance to a fifth distance, based on the feed efficiency, the fourth distance being a distance that is derived by subtracting the third distance from the first distance, and
• causing the feed portion to feed the work cloth in accordance with second data, the second data being data for feeding the work cloth over the fifth distance.