若\(x\)，\(y\)满足约束条件\( \begin{cases} x+y\geqslant 1 \\ x-y\geqslant -1 \\ 2x-y\leqslant 2\end{cases}\)目标函数\(z=ax+2y\)仅在点\((1,0)\)处取得最小值，则\(a\)的取值范围是 ______ ．