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Try to set the f.07 parameter in the invert(frequency 300=18000RPM),calculate the right frequency equal to the RPM(accurate to percentile),then set the new parameter into it . 

Anyway,Do not change the invert settings usually,because we had settled well before leave our factory.

Put a MDF board on the table, control the machine to drill 4 holes at 4 corners of  rectangular(it is according to your machine size, if it is 1530 then drill the holes at 1500X3000mm area), measure its diagonal length, then you will find one diagonal longer than the other, loose the longer side linear block screws (8pcs), remove the other side motor plug(so it will not move), and move the longer side a little forward until the gantry is totally vertical to the Y axis of the machine, then fix all the linear block screws again.

After you adjust the Y axis linear blocks, you can drill 4 holes on the machine 4 corners then measure if the diagonal length to be the same or not, if not the same, then need to adjust again according to which side is shorter or longer.